JP3459245B2 - DC-DC converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for protecting a step-down DC-DC converter from overvoltage, and more particularly to protecting the DC-DC converter from overvoltage on the output side or overvoltage on the output side. Regarding technology to prevent. Or tidal current-DC converter (DC-DC CONV
The present invention relates to a technique for protecting an ERTER circuit and a load when an overvoltage occurs.

[0002]

2. Description of the Related Art A portable electronic device such as a notebook personal computer is equipped with a battery as a power source for the device. It is desirable that the battery mounted on the portable electronic device can supply a constant voltage in order to stabilize the operation of the device.

On the other hand, a general battery has a characteristic that the voltage decreases as the discharge progresses. Therefore, the portable electronic device is equipped with a DC-DC converter that makes the output voltage of the battery constant.

Also, as one of the performances of portable electronic equipment, the time during which the battery is effectively operated (effective operating time)
is important. To keep this effective operating time long,
In addition to reducing the power consumption of portable electronic devices, DC-DC CONVERT
It is necessary to improve the conversion efficiency of ER). Because, DC-DC converter (DC-DC CONVE
This is because the conversion efficiency of RTER) is directly reflected on the power consumption rate of the battery.

DC-DC converter (DC-DC CON
As a method for improving the conversion efficiency of VERTER, a synchronous rectification type DC-DC converter (DC-DC CON) is used.
VERTER) is generally used. This synchronous rectification type DC-DC converter (DC-DC CON
According to VERTER), the conversion efficiency can be improved by about 10% as compared with the conventional DC-DC CONVERTER.

A DC-DC converter (DC-DC)
The conversion efficiency of CONVERTER is also affected by the performance of the capacitor of the DC-DC converter. For example, a recent direct current-direct current converter (DC-DC CONVERTER) emits a high frequency in order to improve conversion efficiency and downsize the device. Such a direct current-direct current converter (DC-DC CONVERTER) requires a smoothing capacitor at the output part in order to reduce the phase error.

The smoothing capacitor has an equivalent series resistance (E
SR), and if the resistance value of this equivalent series resistance (ESR) is large, a DC-DC converter (DC-DC CO)
NVERTER) conversion efficiency deteriorates.

Therefore, a DC-DC converter (DC-DC)
In order to improve the conversion efficiency of CONVERTER, a capacitor having a small equivalent series resistance (ESR) is required.

An organic capacitor is a capacitor having a small equivalent series resistance (ESR). When an organic capacitor is used as the smoothing capacitor, the conversion efficiency of the direct current-direct current converter (DC-DC CONVERTER) is improved, so heat generation is reduced even when a large current is applied. For this reason, a DC-DC converter using an organic capacitor (DC-DC CONVERTER) has come to be used in a device compatible with a large current of about 3 amps to 5 amps.

A direct current-direct current converter (DC-DC CONVE) using an organic capacitor as a smoothing capacitor.
When the RTER) is used in a device compatible with a large current, a large current is input to the DC-DC converter (DC-DC CONVERTER), and the DC-DC converter (D
The capacitor used for the input part of the C-DC CONVERTER is also preferably an organic capacitor having a large allowable ripple.

By the way, the organic capacitor has the advantage of being excellent in the high frequency characteristic and the temperature characteristic as described above, but has the drawback that it is easily destroyed by an overvoltage and causes smoke and ignition.

Therefore, a DC-DC converter (DC-D
When an organic capacitor is used for C CONVERTER), a mechanism for protecting the organic capacitor from overvoltage is required.

DC-DC converter (DC-DC CON
The cause of the overvoltage in the VERTER) is a case where the overvoltage occurs in the output part due to a circuit failure in the DC-DC converter (DC-DC CONVERTER), a battery or charger failure, or an improper battery. DC-DC converter (DC-DC CON
It is considered that an overvoltage is input to (VERTER).

First, a DC-DC converter (DC-DC)
If an overvoltage occurs at the output part of the CONVERTER, a DC-DC converter (DC-DC CONVERT)
It is necessary to protect the smoothing capacitor provided in the output part of (ER).

As a method of protecting the smoothing capacitor, a DC-DC CONVERTE device is used.
There is a method of providing a ZENER diode in the output part of R). In this method, a DC-DC converter (DC-D
The voltage output from C CONVERTER) is ZEN
If the standard voltage of the ER diode is exceeded, the ZENER diode will burn out, and the DC-DC converter (DC-DC C
ONVERTER) and the load are short-circuited.

In this case, a DC-DC converter (DC-D
Since the current flow is stopped by the short circuit between the C CONVERTER) and the load, it is possible to prevent the overvoltage from being applied to the organic capacitor.

A DC-DC converter (DC-DC)
When the overvoltage is input to the converter, it is necessary to protect the capacitor provided in the input part of the direct current-direct current converter (DC-DC converter).

However, conventionally, the protection of the capacitor provided in the input portion of the DC-DC converter is not considered important. Because, DC-DC converter (DC-DC CONVERT
The ER has a mechanism for disconnecting the path of the input voltage, and therefore has a DC-DC converter (DC-DC CONV).
This is because it does not directly affect the circuit provided in the output part of the ERTER).

Here, a DC-DC converter (DC-DC)
A specific example of CONVERTER) will be described based on FIG. Although not shown in FIG. 12, a DC-DC converter (DC-DC CONVERTER) is provided between the battery and the load. This DC-DC converter (DC-DC CONVERTER) includes a main switching transistor Tr1, a synchronous rectification transistor Tr2, a diode D1, a resistor R1, a capacitor C1,
It includes a choke coil L1 and a control circuit CTL. Furthermore, a DC-DC converter (DC-DC CON
A ZENER diode D2 is provided in the output part of VERTER).

Main switching transistor Tr1
Is a field effect transistor (FET), which is turned on and off by a signal DH from the control circuit CTL.

The choke coil L1 is a coil for voltage conversion. The diode D1 is a freewheel diode for releasing the energy accumulated in the choke coil L1 to the output side while the main switching transistor Tr1 is in the off state.

The synchronous rectification transistor Tr2, like the diode D1, is a main switching transistor T2.
It is a switch circuit for a free wheel that releases the energy accumulated in the choke coil L1 to the output side while r1 is in the off state. This synchronization control transistor Tr2
Is a field effect transistor (FET) which can be turned on and off by a signal DL from the control circuit CTL.

For example, the synchronous rectification transistor Tr2
Turns on when the voltage applied to the diode D1 is in the forward direction and turns off when the voltage is in the reverse direction. The resistor R1 is a DC-DC converter (DC-DC CONV).
Sense resistor R1 for measuring the value of the current flowing from (ERR) to the load.

The capacitor C1 is a smoothing capacitor for removing the AC component of the signal output from the sense resistor R1. The ZENER diode D2 is a capacitor C1.
The protection circuit monitors whether or not the voltage from which the AC component is removed is equal to or lower than the standard voltage, that is, whether or not the voltage from which the AC component is removed by the capacitor C1 is an overvoltage.

The ZENER diode D2 is turned on when the voltage of which the AC component is removed by the capacitor C1 exceeds the standard voltage, and is turned on.
Clamp the output voltage from DC CONVERTER) to the standard voltage. Furthermore, if the overvoltage increases, Z
The ENER diode D2 burns out and short-circuits between the DC-DC converter and the load.

The voltage from the battery, the voltage CS input to the sense resistor R1 and the voltage FB output from the sense resistor R1 are input to the control circuit CTL. Furthermore, an ON command value or an OFF command value from the outside and a target voltage Vref are input to the control circuit CTL.

The control circuit CTL obtains the potential difference between the voltage CS input to the sense resistor R1 and the voltage FB output from the sense resistor R1, and determines the DC-DC converter (DC-
The current value output from DC CONVERTER) is measured.

Further, the control circuit CTL compares the output voltage FB from the resistor R1 with a target voltage Vref from the outside, and compares the output voltage FB with a target voltage Vref from the outside (DC-DC CONVERT).
The main switching transistor Tr1 and the synchronous rectification transistor Tr2 are switched on and off so that the output voltage value of (ER) becomes a predetermined voltage value.

The above DC-DC converter (DC-DC
If the CONVERTER) is operating normally, a DC-DC CONVERTER (DC-DC CONVERTER)
Output voltage is sufficiently lower than the standard voltage of the ZENER diode D2, the ZENER diode D2 is turned off. In this case, the voltage from which the AC component has been removed by the capacitor C1 is directly input to the load.

On the other hand, a DC-DC converter (DC-DC
When the output voltage of the CONVERTER becomes an overvoltage, a DC-DC CONVERT device (DC-DC CONVERT)
The output voltage value of (ER) becomes higher than the standard voltage value of the ZENER diode D2. When the output voltage becomes higher than the standard voltage, the ZENER diode D2 is turned on.
In this case, a DC-DC converter (DC-DC CONV
ERRTER) output voltage is ZENER diode D2
It is clamped to the standard voltage of. This can prevent overvoltage from being applied to the load.

Further, the above DC-DC converter (DC
Since -DC CONVERTER does not have a mechanism for limiting the current flowing through the ZENER diode D2, the ZENER diode D2 burns out if the overvoltage continues. In this case, a DC-DC converter (DC-DC CONVE
(RTER) and the load are short-circuited. As a result, no current flows in the smoothing capacitor C1, and it is possible to prevent the smoothing capacitor C1 from burning.

Further, a DC-DC converter (DC-DC
As a method of causing a load short circuit when an overvoltage condition occurs in the CONVERTER, a thyristor (SC
Although there is also a method of using R), there is a problem that the number of parts of the device is increased and the size of the circuit is increased and the production cost is increased.

On the other hand, a DC-DC converter (DC-DC
When an overvoltage is input to (CONVERTER), the control circuit CTL turns off the main switching transistor. In this case, a DC-DC converter (DC-D
Since no current flows in the C CONVERTER, a DC-DC converter (DC-DC CONVERTER)
It does not affect the circuit of the output part of (TER). Therefore, a DC-DC converter (DC-DC CO
NVERTER) does not have a protection mechanism against an overvoltage on the input side.

[0034]

By the way, when a Zener diode is used to protect a capacitor, it functions as a protection circuit if the Zener diode fails in a short mode, but as a protection circuit if it fails in an open mode. Does not function. ZEN
If the ER diode fails in open mode,
DC-DC CONVERTE
There is a problem that the organic capacitor provided at the output part of R) is burnt out and causes smoke or ignition.

Furthermore, since it is impossible to specify whether the ZENER diode fails in the open mode or in the short mode, it is possible to use the ZENER diode as a protection circuit for the DC-DC converter. It is inappropriate to use a diode.

On the other hand, a method of using a high withstand voltage organic capacitor may be considered in order to prevent the organic capacitor from burning due to overvoltage. However, since the high withstand voltage organic capacitor has a small capacity, it is necessary to obtain a desired capacity. Requires multiple organic capacitors. Therefore, there is a problem that the circuit becomes large. Furthermore, since the high withstand voltage organic capacitor has a large equivalent series resistance (ESR),
DC-DC CONVERTE
There is also a problem that the conversion efficiency of R) is deteriorated.

On the other hand, in order to prevent burning of the organic capacitor due to overvoltage, a DC-DC converter (DC-
There is a method of providing a fuse for preventing burnout to each of the organic capacitors used for DC CONVERTER). However, in this method, a DC-DC converter (DC
-At the same time that the number of components of the DC CONVERTER increases, a DC-DC CONV device (DC-DC CONV)
There is a problem that the production cost of ERTER) increases. Further, when a fuse is provided for each organic capacitor, a DC-DC converter (DC
There is a problem that the conversion efficiency of -DC CONVERTER) decreases.

A DC-DC converter (DC-DC)
Since organic capacitors have been used for the input part of the CONVERTER), it is also necessary to protect these organic capacitors.

Therefore, the present invention has been made in view of the above problems, and in a step-down DC-DC converter of the synchronous rectification type (DC-DC CONVERTER),
A DC-DC converter (DC-DC CONVERTE) can be used to convert an overvoltage of the output voltage without complicating the circuit configuration.
It is an object of the present invention to prevent smoke and ignition due to overvoltage by providing a technology for protecting R). In addition, a DC-DC converter (DC-DC CONV
It is an object to miniaturize ERTER and improve conversion efficiency. In addition, a DC-DC converter without complicating the circuit configuration.
It is an object of the present invention to prevent an overvoltage from being applied to the load. Further, the present invention has been made in view of the above problems, and in a step-down DC-DC converter of a synchronous rectification system (DC-DC CONVERTER), an overvoltage of an output voltage is prevented without complicating the circuit. It is an object of the present invention to provide a technology for making the device smaller and to contribute to the improvement of reliability.

[0040]

The present invention adopts the following means in order to solve the above problems. First, the first
According to another aspect of the present invention, there is provided storage means for storing electric power from a power supply, a first switch element for switching connection and disconnection of the power supply and the storage means, and the storage means provided between the storage means and the ground. And a connection between the first switch element and the second switch element are controlled so that the output voltage from the storage means maintains a constant value. A DC-DC converter of the synchronous rectification system including a control unit configured to monitor the output voltage from the storage unit and output a signal when the output voltage exceeds a predetermined voltage value. When the signal from the overvoltage detecting means and the overvoltage detecting means is input, the first switch element is controlled to be in a disconnection state and the second switch element is in a connection state. A DC converter - such controls, DC synchronous rectification type that includes a clamping means for clamping the output voltage to the ground level from the storage means.

The above-mentioned overvoltage detecting means compares the reference voltage with the output voltage from the accumulating means by comparing the reference voltage generating means for generating a reference voltage, and when the output voltage becomes larger than the reference voltage. And a voltage comparing means for outputting the signal may be provided.

Also, in the DC-DC converter according to the first aspect of the present invention, when the first switch element fails in a short-circuited state, the second switch element is brought into the connected state and the voltage from the power source is applied. May be further provided with a short-circuit means for short-circuiting, and in addition to the above-mentioned short-circuit means, a cut-off means for shutting off the input from the power source by the power short-circuited by the short-circuit means may be further provided. As the breaking means, a fuse blown by the electric power short-circuited by the short-circuiting means can be exemplified.

The DC-DC converter according to the first invention is provided between the power supply and the first switch element,
You may make it further provide the interruption | blocking means which interrupt | blocks the input from a power supply.

At this time, when the first switch element fails, the clamp means short-circuits the power from the power source by setting the second switch element in the connected state, and the short-circuited power causes the cut-off means to disconnect from the power source. The input of may be blocked.

Next, a second aspect of the invention is to connect a storage means for storing electric power from a power source, a first switch for switching between connection and disconnection of the power source and the storage means, and between the storage means and the ground. A second switch disposed between the storage means and the ground to switch between connection and disconnection, and connection and disconnection of the first and second switches to control the output voltage from the storage means to a constant value. Control means for keeping the voltage, detection means for detecting that the output voltage of the storage means exceeds a predetermined voltage value, and a disconnection state for the first switch in response to the detection by the detection means. And a clamp means for controlling the second switch so that the second switch is connected to the second switch.

The above-mentioned detecting means compares, for example, a reference voltage generating means for generating a reference voltage with the output voltage of the storage means, and outputs a signal when the output voltage of the storage means becomes larger than the reference voltage. May be provided.

Further, in the DC-DC converter according to the second invention, when the first switch fails in the short-circuited state, the second switch is forcibly brought into the connected state so that the power from the power source is May be further provided with a short-circuiting means for short-circuiting, and in addition to the above-mentioned short-circuiting means, a shut-off means for shutting off the input from the power source may be further provided. A fuse can be exemplified as the blocking means.

The DC-DC converter according to the second aspect of the invention may be further provided with a shutoff means provided between the power source and the first switch element for shutting off the input from the power source. . At that time, when the first switch fails, the clamp means short-circuits the power from the power source by setting the second switch to the connected state, and the short-circuited power is used by the shut-off means to input the power from the power source. May be shut off.

Next, a third aspect of the present invention is provided between the storage means for storing electric power from the power supply, the first switch element for switching between connection and disconnection of the power supply and the storage means, and the storage means and the ground. The output voltage from the storage means is controlled to a constant value by controlling the connection and disconnection of the second switch element and the first switch element and the second switch element which are connected to and disconnected from the storage means and the ground. A control circuit for a DC-DC converter of a synchronous rectification system, comprising: a first control means for maintaining the output voltage from the storage means, the output voltage being a predetermined voltage value. And an overvoltage detecting unit that detects that the output voltage exceeds a predetermined voltage value.
A second switch element is controlled to be in a disconnection state and a second switch element is to be in a connection state so that the output voltage from the storage means is set to the ground level. And a control circuit.

The above-mentioned overvoltage detecting means compares the reference voltage generating means for generating a reference voltage with the output voltage from the accumulating means, and the output voltage from the accumulating means is larger than the reference voltage. It may be provided with a voltage comparing means for outputting a signal when it becomes low.

Next, a fourth aspect of the present invention comprises a storage means for storing electric power from a power supply, a first switch element for switching between connection and disconnection of the power supply and the storage means, the storage means and a ground. A second switch element which is provided between the storage means and the ground to switch between connection and disconnection, and a connection and disconnection of the first switch element and the second switch element are controlled to control the storage means from the storage means. Is a control circuit for a DC-DC converter of the synchronous rectification system, comprising: a first control unit for keeping the output voltage of the device at a constant value; and monitoring the output voltage from the storage unit, Detecting means for detecting that the output voltage exceeds a predetermined voltage value;
In response to the detection by the detection means, the first switch element is controlled to be in a disconnection state, and
And a second control means for controlling the switch element to be in a connected state.

When the output voltage of the storage means becomes larger than the reference voltage by comparing the reference voltage with the output voltage from the storage means, the detection means compares the reference voltage with the output voltage from the storage means. And a voltage comparison means for outputting a signal may be provided.

Next, a fifth aspect of the present invention is a synchronous rectification type DC-DC converter, which detects that the output voltage of the main switch, the synchronous rectification switch, and the DC-DC converter is an overvoltage. Outputs an overvoltage detection unit and a first control signal for turning off the main switch and a second control signal for turning on the synchronous rectification switch when the overvoltage detection unit detects an overvoltage. The DC-DC converter of the synchronous rectification system, which comprises:

The DC-DC converter according to the fifth aspect of the present invention may further include an inductor connected to the main switch and a capacitor connected to the inductor to smooth the output voltage from the inductor. good.

The DC-DC converter according to the fifth aspect of the present invention further comprises feedback means for feedback controlling the main switch and the synchronous rectification switch so as to keep the output voltage of the DC-DC converter constant. May be.

The DC-DC converter according to the fifth aspect of the present invention may further include a shutoff means provided between the main switch and the power source for shutting off the input from the power source.

Next, a sixth aspect of the present invention is, in a synchronous rectification type DC-DC converter, detects that the output voltage of the main switch, the synchronous rectification switch, and the DC-DC converter is an overvoltage. An overvoltage detection means, and a control means for controlling to forcibly turn off the main switch and forcibly turn on the synchronous rectification switch when the overvoltage detection means detects an overvoltage. , A synchronous rectification type DC-DC converter.

A DC-DC converter according to the sixth invention comprises:
An inductor connected to the main switch and a capacitor connected to the inductor for smoothing the output voltage from the inductor may be further provided.

In the DC-DC converter according to the sixth aspect of the invention, the overvoltage detecting means detects, for example, that the output voltage of the DC-DC converter is an overvoltage,
You may make it output a detection signal.

Correspondingly, when the detection signal is output from the overvoltage detection means, the control means stores the detection signal and synchronously rectifies it with the first control signal for turning off the main switch. A memory circuit for outputting a second control signal for turning on the power switch may be provided.

Then, the control means outputs a second control signal to turn on the synchronous rectification switch when the main switch fails in the short circuit state, thereby short-circuiting the input from the power supply. May be.

The DC-DC converter according to the sixth aspect of the present invention further comprises feedback means for feedback controlling the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter constant. May be. Further, the DC-DC converter according to the sixth aspect of the present invention may further include a cutoff unit that is provided between the main switch and the power supply and that cuts off an input from the power supply.

Next, a seventh aspect of the present invention is a control circuit for controlling a DC-DC converter of the synchronous rectification type which comprises a main switch and a switch for synchronous rectification, and which is an output of the DC-DC converter. An overvoltage detecting means for detecting that the voltage is an overvoltage, and a first for turning off the main switch when the overvoltage detecting means detects the overvoltage.
And a control means for outputting a second control signal for turning on the synchronous rectification switch.

An eighth invention is that a main switch,
For controlling a synchronous rectification type DC-DC converter including a synchronous rectification switch, an inductor connected to the main switch, and a capacitor connected to the inductor for smoothing an output voltage from the inductor. A control circuit for detecting that the output voltage of the DC-DC converter is an overvoltage; and a first circuit for turning off the main switch when the overvoltage detection unit detects an overvoltage. Control means for outputting a control signal of No. 1 and a second control signal for turning on the switch for synchronous rectification.

A ninth aspect of the present invention is a control circuit for controlling a synchronous rectification type DC-DC converter comprising a main switch and a synchronous rectification switch, wherein the output of the DC-DC converter is a control circuit. Overvoltage detection means for detecting that the voltage is an overvoltage, and when the overvoltage detection means detects an overvoltage, the main switch is forcibly turned off and the synchronous rectification switch is forcibly turned on. And a control means for controlling so that In the above seventh to ninth inventions, the overvoltage detecting means is
A detection signal may be output when it is detected that the output voltage of the DC-DC converter is an overvoltage.

Correspondingly, when the detection signal is output from the overvoltage detection means, the control means stores the detection signal, and the first control signal for turning off the main switch and the synchronization signal. A memory circuit that outputs a second control signal for turning on the rectifying switch may be provided. Further, the control means may short-circuit the input from the power source by outputting a second control signal for turning on the synchronous rectification switch when the main switch fails.

A tenth aspect of the present invention is a main switch, a switch for synchronous rectification, an inductor connected to the main switch, a capacitor connected to the inductor for smoothing an output voltage from the inductor,
A control circuit for controlling a DC-DC converter of a synchronous rectification system comprising: an overvoltage detecting unit for detecting that the output voltage of the DC-DC converter is an overvoltage; and the overvoltage detecting unit is an overvoltage detector. And a control means for controlling the main switch to be forcibly turned off and the synchronous rectification switch to be forcibly turned on.

The control circuit according to the tenth aspect of the present invention may further include feedback means for feedback controlling the main switch and the synchronous rectification switch so as to keep the output voltage of the DC-DC converter at a constant value.

The eleventh aspect of the present invention is a control circuit for controlling a DC-DC converter of the synchronous rectification type which comprises a main switch and a switch for synchronous rectification, and a request for stopping the DC-DC conversion process. Receiving means for receiving a signal, and a first control signal for turning off the main switch and a second control for turning on the synchronous rectification switch when the receiving means receives the stop request signal Control means for outputting a signal.

The control means is a second switch for turning on the synchronous rectification switch when the main switch fails.
The input from the power supply may be short-circuited by outputting the control signal.

A twelfth aspect of the invention is to connect a main switch, a synchronous rectification switch, an inductor connected to the main switch, and an inductor connected to the main switch,
A control circuit for controlling a DC-DC converter of a synchronous rectification system, which comprises a capacitor for smoothing an output voltage from the inductor, a receiving means for receiving a DC-DC conversion process stop request signal, and Control means for outputting a first control signal for turning off the main switch and a second control signal for turning on the synchronous rectification switch when the receiving means receives the stop request signal. .

The control means is a second switch for turning on the synchronous rectification switch when the main switch fails.
The input from the power supply may be short-circuited by outputting the control signal.

The thirteenth aspect of the present invention is a control circuit for controlling a DC-DC converter of the synchronous rectification type which comprises a main switch and a switch for synchronous rectification, and a DC-DC conversion process stop request. Receiving means for receiving a signal, and control for forcibly turning off the main switch and forcibly turning on the synchronous rectification switch when the receiving means receives the stop request signal. And means.

The fourteenth aspect of the invention is to connect a main switch, a synchronous rectification switch, an inductor connected to the main switch, and an inductor to the main switch,
In a control circuit for controlling a DC / DC converter of a synchronous rectification system, which comprises a capacitor for smoothing an output voltage from the inductor, a receiving unit for receiving a DC / DC conversion process stop request signal, and the receiving unit. When the stop request signal is received, a control means for instructing to forcibly turn off the main switch and a control means for controlling to forcibly turn on the synchronous rectification switch are provided.

The stop request signal according to the above-mentioned first to fourteenth inventions may be a signal indicating that the output voltage of the DC-DC converter is an overvoltage. In addition, the control circuit according to the above-mentioned first to fourteenth aspects of the present invention further includes feedback means for feedback controlling the main switch and the synchronous rectification switch in order to maintain the output voltage of the DC-DC converter at a constant value. May be.

Next, a fifteenth aspect of the present invention is a control circuit for controlling a DC-DC converter of the synchronous rectification system, which comprises a main switch and a switch for synchronous rectification, and a request for stopping the DC-DC conversion process. When the receiving means receives a signal and the stop request signal is received by the receiving means, the main switch is controlled to be turned off and the synchronous rectification switch is turned on to control the DC-DC conversion. Control means for stopping the output of the device.

A sixteenth aspect of the present invention is a control circuit for controlling a synchronous rectification type DC-DC converter comprising a main switch and a synchronous rectification switch, wherein the output voltage of the DC-DC converter is A voltage input terminal for inputting, and an overvoltage detection unit that outputs a detection signal when it is detected that the voltage input to the voltage input terminal exceeds a predetermined voltage, and the overvoltage detection unit outputs a detection signal, Clamping means for clamping the output of the DC-DC converter to the ground level by controlling the main switch to be turned off and the synchronous rectification switch to be turned on.

[0078]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. <First Embodiment> FIG. 1 is a diagram showing a first embodiment of a DC-DC converter of the present invention. In the figure, the same names and reference numerals are added to the same components as the conventional ones.

DC-DC converter (DC-DC CON
VERTER) is provided between a battery as a power source and a load. (DC-DC converter (DC-DC CON
Configuration of VERTER) The DC-DC converter according to the present embodiment includes a control circuit CTL and a main switching transistor Tr.
1, a transistor Tr2 for synchronous rectification, a diode D1,
Choke coil L1, capacitor C1, voltage comparator IC
2 and a power supply e3 that generates a reference voltage e3.

(DC-DC converter (DC-DC CO
NVERTER) Connection Form of Circuits) First, the connection form of the above-described components will be described.

The main switching transistor Tr1 is connected to the battery via the signal line 14. The main switching transistor Tr1 is connected to the choke coil L1 via the signal line 1 and is connected to the control circuit CTL via the signal line 24.

The above main switching transistor T
r1 is, for example, a MOS-FET (Met) having three terminals of a source terminal, a drain terminal, and a gate terminal.
alOxide Semiconductor Fie
ld Effect Transistor).
In this case, the signal line 14 is connected to the drain terminal of the main switching transistor Tr1. Also,
The signal line 1 is the main switching transistor T
It is connected to the source terminal of r1. Further, the signal line 24 is connected to the gate terminal of the main switching transistor Tr1.

The choke coil L1 connected to the main switching transistor Tr1 via the signal line 1 is further connected to the resistor R1 via the signal line 15. Resistance R
1 is connected to a load via a signal line 16.

A signal line 19 is provided in the middle of the signal line 14.
Are connected. The signal line 19 is connected to the control circuit CTL. In addition, the main switching transistor Tr
Two signal lines 2 and 3 are connected in the middle of the signal line 1 that connects 1 and the choke coil L1.

Of the above two signal lines 2 and 3, the signal line 2 near the main switching transistor Tr1 is connected to the synchronous rectification transistor Tr2. The synchronous rectification transistor Tr2 is connected to the control circuit CTL via the signal line 25 and is also connected to the ground via the signal line 26.

The synchronous rectification transistor Tr2 has, for example, a MOS-FET (Metal Oxide) having three terminals of a drain terminal, a source terminal and a gate terminal.
It is a semiconductor FET). In this case, the signal line 2 is connected to the synchronous rectification transistor Tr.
2 drain terminal. The signal line 25 is
It is connected to the gate terminal of the synchronous rectification transistor Tr2. The signal line 26 is a transistor for synchronous rectification Tr.
2 is connected to the source terminal.

Of the above two signal lines 2 and 3, the signal line 3 near the choke coil L1 is connected to the cathode terminal of the diode D1. The anode terminal of the diode D1 is connected to the ground via the signal line 27.

One signal line 20 is connected in the middle of the signal line 15 connecting the choke coil L1 and the resistor R1. The signal line 20 is connected to the control circuit CTL and controls the voltage value CS input to the resistor R1 to the control circuit CTL.
Is a signal line for input to.

Signal line 1 connecting the resistor R1 and the load
In the middle of 6, three signal lines 4, 5, 21 are connected. Of the three signal lines 4, 5, and 21, the signal line 4 near the resistor R1 is connected to the control circuit CTL. The signal line 4 is a DC-DC converter (DC-DC CONV).
The voltage value FB output from the control circuit CT
It is a signal line for feeding back to L.

Of the three signal lines 4, 5, and 21, the middle signal line 5 is connected to the ground via the smoothing capacitor C1. Of the three signal lines 4, 5, and 21, the signal line 21 near the load is connected to the voltage comparator IC2. The voltage comparator IC2 is, for example, a voltage comparator having a non-inverting input terminal, an inverting input terminal, and an output terminal.

In this case, the signal line 21 is connected to the non-inverting input terminal of the voltage comparator IC2. The inverting input terminal of the voltage comparator IC2 is connected to the power source e3 via the signal line 28.
Connected to. The output terminal of the voltage comparator IC2 is connected to the control circuit CTL via a signal line 29.

(DC-DC converter (DC-DC CO
Function of Circuit Constituting NVERTER) Next, the function of each of the above components will be described.

(Main switching transistor Tr
1) The main switching transistor Tr1 receives the control signal DH from the control circuit CTL, and the input signal D
According to H, the signal line 14 and the signal line 1 are connected or disconnected.

For example, the main switching transistor Tr1 is turned on when a voltage from the control circuit CTL is applied to its gate terminal, connects the drain terminal and the source terminal, and connects the signal line 14 and the signal line 1 to each other. Connect between and.

Further, the main switching transistor T
r1 is turned off unless the voltage from the control circuit CTL is applied to the gate terminal, disconnects the drain terminal and the source terminal, and disconnects the signal line 14 and the signal line 1.

(Choke coil L1) Choke coil L
Reference numeral 1 is a coil for voltage conversion. (Resistance R1) Resistance R
1 is a DC-DC converter
TER) is a sense resistor that senses the output current value.

(Diode D1) The diode D1 is a free wheel diode for releasing the energy accumulated in the choke coil L1 to the output side when the main switching transistor Tr1 is in the off state.

(Synchronous Rectification Transistor Tr2) The synchronous rectification transistor Tr2 receives the signal DL from the control circuit CTL and connects or disconnects the signal line 2 and the signal line 26 in accordance with the input signal DL. Is.

For example, the synchronous rectification transistor Tr2
Is turned on when a voltage from the control circuit CTL is applied to the gate terminal, connects the drain terminal and the source terminal, and connects the signal line 2 and the signal line 26.

The synchronous rectification transistor Tr2 is turned off unless the voltage from the control circuit CTL is applied to the gate terminal, disconnects the drain terminal and the source terminal, and connects the signal line 2 and the signal line 26. Disconnect between and.

In this example, the synchronous rectification transistor T
r2 is a switch circuit for a free wheel that outputs the energy accumulated in the choke coil L1 when the main switching transistor Tr1 is in the off state.

For example, the synchronous rectification transistor Tr2
Is in an ON state (a state in which the signal line 2 and the signal line 26 are connected) when the voltage applied to the diode D1 is in the forward direction, and is OFF when the voltage applied to the diode D1 is in the reverse direction. The state (the state in which the signal line 2 and the signal line 26 are disconnected) is set. At this time, the voltage drop of the diode D1 is reduced.

(Capacitor C1) The capacitor C1 is a smoothing capacitor for removing the pulsating component contained in the voltage output from the choke coil L1.

(Power Supply e3) The power supply e3 generates a reference voltage e3 which is a voltage output from the DC-DC converter (DC-DC CONVERTER).

(Voltage Comparator IC2) Voltage Comparator IC2
Is a DC-DC CONVERT device.
The output voltage of (ER) is input via the signal line 21, and at the same time, the reference voltage e3 from the power supply e3 is input. And
The voltage comparator IC2 is a DC-DC converter (DC-DC).
The output voltage of CONVERTER) is compared with the reference voltage e3 from the power supply e3, and the signal OV indicating the comparison result is output.

For example, the voltage comparator IC2 subtracts the reference voltage e3 from the output voltage of the DC-DC converter (DC-DC CONVERTER), and outputs a Low level signal if the subtraction result is "0" or less. , If the subtraction result is a positive value, a High level signal is output.

(Control Circuit CTL) The control circuit CTL includes
In addition to the signal lines 19, 24, 25, 4, 20, and 29 described above, an on command value or off command value from the outside and a target voltage Vref from the outside are input. The target voltage Vref from the outside is a DC-DC converter (DC-DC).
CONVERTER) is a reference voltage of a voltage to be output.

The control circuit CTL receives the signal OV from the voltage comparator IC2 and the voltage value FB input via the signal line 4.
And a DC-DC converter (DC-DC CONVERT
The main switching transistor Tr1 and the synchronous rectification transistor Tr2 are switched between the on state and the off state according to the target voltage Vref of the voltage to be output from (ER).

Here, the internal structure of the control circuit CTL will be described. (Configuration of control circuit CTL) Control circuit CTL
2 is a circuit that employs a pulse width modulation method (PWM method) as shown in FIG.
PWM comparator 9, charge pump circuit 12, synchronous rectification control circuit 13, flip-flop FF, drive-1 (1
0) and a drive-2 (11). Further, the control circuit CTL includes the dividing resistors R2 / R3, the error amplifiers ERA1 and ERA2, the logical product circuit AND1, and
The OR circuit OR1 is provided.

(Power Supply 7) The power supply 7 supplies operating power to the circuits forming the control circuit CTL when an ON command value is input from the outside. Further, the power supply 7 stops the supply of operating power to the circuits forming the control circuit CTL when an OFF command value from the outside is input.

(Triangular Wave Oscillator 8) The triangular wave oscillator 8 oscillates a conversion triangular wave for converting a voltage into a pulse width at a constant frequency. The triangular wave oscillated from the triangular wave oscillator 8 is input to the PWM comparator 9.

(Dividing resistor R2 / R3) Dividing resistor R2 / R
Reference numeral 3 is connected to the signal line 4 and is adapted to input the output voltage FB of the DC-DC converter (DC-DC CONVERTER). This dividing resistor R2 / R3
Is a sense resistor for sensing the voltage value of the output voltage FB.

The voltage value sensed by the dividing resistor R2 / R3 is input to the error amplifier ERA1.

(Error Amplifier ERA1) Error Amplifier E
RA1 inputs the voltage value FB sensed by the dividing resistors R2 / R3 and the target voltage Vref from the outside,
The error amplification circuit amplifies an error between the voltage value FB and the target voltage Vref. The error amplified by the error amplifier ERA1 is input to the non-inverting input terminal of the PWM comparator 9.

(PWM Comparator 9) The PWM comparator 9 is a voltage comparator having an inverting input terminal and a non-inverting input terminal. The inverting input terminal of the PWM comparator 9 is the triangular wave oscillator 8
Input the conversion triangular wave output from. The signal output from the error amplifier ERA1 is input to the non-inverting input terminal of the PWM comparator 9.

The PWM comparator 9 compares the signal input to the non-inverting input terminal with the signal input to the inverting input terminal. For example, the PWM comparator 9 subtracts the signal input to the inverting input terminal from the signal input to the non-inverting input terminal. The PWM comparator 9 keeps the value obtained by subtraction showing a negative value (while the signal output from the triangular wave oscillator 8 is larger than the signal output from the error amplifier ERA1).
Outputs a high level signal.

On the other hand, the PWM comparator 9 maintains the value obtained by the subtraction while the value is positive (while the signal output from the triangular wave oscillator 8 is smaller than the signal output from the error amplifier ERA1). It outputs a low level signal.

The signal output from the PWM comparator 9 in this manner is the AND circuit AND1 and the synchronous rectification control circuit 1
It is input to 3 and.

(Error Amplifier ERA2) Error Amplifier E
RA2 is a DC-DC converter (DC-DC CONV
The output voltage FB of (ERTER) is input via the signal line 4, and at the same time, the voltage value CS input to the resistor R1 is input via the signal line 20.

The error amplifier ERA2 obtains the potential difference between the output voltage FB of the DC-DC converter (DC-DC CONVERTER) and the voltage value CS, and outputs the current output from the DC-DC converter (DC-DC CONVERTER). This is an error amplification circuit that measures a value.

The voltage value output from the error amplifier ERA2 is input to the synchronous rectification control circuit 13.

(Charge Pump Circuit 12) The charge pump circuit 12 includes the main switching transistor Tr1.
Is supplied to the drive-1 (10) and the voltage for driving the synchronous rectification transistor Tr2 is driven-
2 (11).

(Synchronous Rectification Control Circuit 13) The synchronous rectification control circuit 13 inputs the signal output from the PWM comparator 9 and the signal output from the error amplifier ERA2. The synchronous rectification control circuit 13 is a circuit that performs synchronous rectification by switching the synchronous rectification transistor Tr2 between the on state and the off state according to the signal from the PWM comparator 9 and the signal from the error amplifier ERA2.

For example, the synchronous rectification control circuit 13 uses the PWM
A High level signal is output only when the Low level signal from the comparator 8 is input and the signal from the error amplifier ERA2 is below a certain value.

The signal output from the synchronous rectification control circuit 13 is input to the OR circuit OR1.

(Flip-Flop FF) The flip-flop FF has two input terminals, a set terminal and a reset terminal, and a non-inverting output terminal Q and an inverting output terminal * Q.
It has two output terminals.

The set terminal S of the flip-flop FF is
The signal OV from the voltage comparator IC2 is input. At this time, the flip-flop FF stores the signal input to the set terminal.

Reset terminal R of flip-flop FF
Inputs an ON command value or an OFF command value from the outside. When the ON command value or the OFF command value is input to the reset terminal, the signal stored in the flip-flop FF is reset to the Low level signal.

Non-inverting output terminal Q of flip-flop FF
Is connected to the OR circuit OR1. This output terminal Q
Outputs the signal stored in the flip-flop FF as it is.

For example, a DC-DC converter (DC-DC
CONVERTER) output voltage FB is reference voltage e3
In the following cases, the set terminal S of the flip-flop FF inputs a Low level signal as the signal OV from the voltage comparator IC2. In this case, the flip-flop F
F stores the low-level signal input to the set terminal S, and the non-inverting output terminal Q outputs the low-level signal stored in the flip-flop FF.

A DC-DC converter (DC-DC)
When the output voltage FB of CONVERTER) exceeds the reference voltage e3 (when the output voltage FB becomes an overvoltage),
The set terminal S of the flip-flop FF has a voltage comparator I
A high level signal is input as the signal OV from C2. In this case, the flip-flop FF has the set terminal S
The high-level signal input to is stored, and the non-inverting output terminal Q outputs the high-level signal stored in the flip-flop FF.

Inversion output terminal * Q of flip-flop FF
Is connected to the AND circuit AND1. The inverting output terminal * Q outputs a value obtained by inverting the signal value stored in the flip-flop FF, that is, a signal obtained by inverting the Low level and the High level.

For example, if the signal OV stored in the flip-flop FF is a signal of low level, the inverting output terminal * Q is (DC-DC CONV
If the output voltage FB of ERRTER) is equal to or lower than the reference voltage e3), a high level signal is output. Further, if the signal OV stored in the flip-flop FF is a high level signal, the output voltage FB of the DC-DC converter (DC-DC CONVERTER) exceeds the reference voltage e3 at the inverting output terminal * Q. If), L
An ow level signal will be output.

(Logical product circuit AND1) logical product circuit AND
1 inputs the signal output from the PWM comparator 9 and the signal output from the inverting output terminal * Q of the flip-flop FF. This logical product circuit AND1 includes a PWM comparator 9
AND the signal from the flip-flop FF, and outputs a signal indicating the result of the operation. The signal output from the AND circuit AND1 is the drive-1
It is input in (10).

For example, a DC-DC converter (DC-DC
CONVERTER) output voltage FB is reference voltage e3
In the following cases, the AND circuit AND1 inputs the high level signal from the inverting output terminal * Q of the flip-flop FF. In this case, the AND circuit AND1
Outputs the signal from the PWM comparator 9 as it is. As a result, when the output voltage FB is equal to or lower than the reference voltage e3, the drive-1 (10) operates according to the signal from the PWM comparator 9.

In addition, a DC-DC converter (DC-DC
When the output voltage FB of the CONVERTER) becomes larger than the reference voltage e3 (when the output voltage FB becomes an overvoltage), the AND circuit AND1 operates the flip-flop FF.
A low level signal is input from the inverting output terminal * Q of. In this case, the AND circuit AND1
A low level signal is output regardless of the signal from the M comparator 9. As a result, when the output voltage FB becomes an overvoltage, the drive-1 (10) operates according to the low level signal from the flip-flop FF regardless of the signal from the PWM comparator 9.

(OR circuit OR1) OR circuit OR1
Inputs the signal output from the synchronous rectification control circuit 13 and the signal output from the non-inverting output terminal Q of the flip-flop FF. The logical sum circuit OR1 calculates the logical sum of the signal from the synchronous rectification control circuit 13 and the signal from the flip-flop FF, and outputs a signal indicating the calculation result. The signal output from the OR circuit OR1 is input to the drive-2 (11).

For example, a DC-DC converter (DC-DC
CONVERTER) output voltage FB is reference voltage e3
In the following cases, the OR circuit OR1 inputs the low level signal from the non-inverting output terminal Q of the flip-flop FF. In this case, the OR circuit OR1 outputs the signal from the synchronous rectification control circuit 13 as it is. As a result, when the output voltage FB reference voltage e3 or less, the drive-2 (11) determines that the synchronous rectification control circuit 13
It will operate according to the signal from.

In addition, a DC-DC converter (DC-DC
When the output voltage FB of CONVERTER) becomes larger than the reference voltage e3 (when the output voltage FB becomes an overvoltage), the OR circuit OR1 outputs the high level signal from the non-inverting output terminal Q of the flip-flop FF. Will be input. In this case, the OR circuit OR1 outputs a high level signal regardless of the signal from the synchronous rectification control circuit 13. As a result, the output voltage FB
Is overvoltage, the drive-2 (11) operates according to the high level signal from the flip-flop FF regardless of the signal from the synchronous rectification control circuit 13.

(Drive-1 (10)) Drive-1
(10) is in accordance with the signal from the AND circuit AND1
The main switching transistor Tr1 is switched between an on state and an off state.

For example, the drive-1 (10) supplies the power supplied from the charge pump circuit 12 to the main switching transistor Tr1 when the high level signal from the AND circuit AND1 is input to the main switching transistor Tr1. The transistor Tr1 is turned on.

Further, the drive-1 (10) stops the power supply to the main switching transistor Tr1 when the low level signal from the AND circuit AND1 is inputted, and the main switching transistor T1 is turned off.
Turn off r1.

(Drive-2 (11)) Drive-2
(11) switches the synchronous rectification transistor Tr2 between the on state and the off state according to the signal from the OR circuit OR1.

For example, the drive-2 (11) supplies the electric power supplied from the charge pump circuit 12 to the synchronous rectification transistor Tr2 when the high level signal from the OR circuit OR1 is input to the synchronous rectification transistor Tr2. The rectifying transistor Tr2 is turned on.

On the other hand, the drive-2 (11) receives the Low-level signal from the OR circuit OR1,
The power supply to the synchronous rectification transistor Tr2 is stopped and the synchronous rectification transistor Tr2 is turned off. (Operation / Effect of First Embodiment) Hereinafter, a DC-DC converter according to the present embodiment (DC-DC CONVE)
The action and effect of RTER will be described.

(1) DC-DC converter (DC-DC
CONVERTER) is operating normally DC-
When the direct current converter (DC-DC CONVERTER) is operating normally, that is, when the output voltage FB of the direct current-direct current converter (DC-DC CONVERTER) shows a normal voltage value, the output voltage FB Is sufficiently smaller than the reference voltage e3, the voltage comparator IC2
Outputs a low level signal.

The low-level signal output from the voltage comparator IC2 is the flip-flop FF of the control circuit CTL.
Is input to the set terminal S of. Then, the flip-flop FF stores the input low-level signal. At this time, the non-inverting output terminal Q of the flip-flop FF is
The low level signal stored in the flip-flop FF is output. The inverting output terminal * Q of the flip-flop FF outputs a high level signal.

Non-inverting output terminal Q of flip-flop FF
The low-level signal output from the OR circuit OR
Input to 1. In this case, the OR circuit OR1 outputs the signal (Low-level signal or High-level signal) from the synchronous rectification control circuit 13 as it is.
The signal output from the OR circuit OR1 is the drive-2
It is input in (11).

The drive-2 (11) is an OR circuit OR.
The synchronous rectification transistor Tr2 is switched between the ON state and the OFF state in accordance with the signal from the signal 1, that is, the signal from the synchronous rectification control circuit 13. As a result, drive-2
(11) can turn on the synchronous rectification transistor Tr2 while the main switching transistor Tr1 is in the off state and the diode D1 is releasing the energy stored in the choke coil L1 to the output side. it can.

The High level signal output from the inverting output terminal * Q of the flip-flop FF is input to the AND circuit AND1. In this case, the AND circuit AN
The D1 outputs the signal (Low level signal or High level signal) from the PWM comparator 9 as it is. The signal output from the AND circuit AND1 is
Input to drive-1 (10).

The drive-1 (10) is an AND circuit AN.
The main switching transistor Tr1 is switched between the on state and the off state according to the signal from D1, that is, the signal from the PWM comparator 9. As a result, drive-
1 (10) turns on the main switching transistor Tr1 when the triangular wave from the triangular wave oscillator 8 is higher than the voltage value from the error amplifier ERA1, and the triangular wave from the triangular wave oscillator 8 is lower than the voltage value from the error amplifier ERA1. At times, the main switching transistor Tr1 can be turned off.

(2) When the signal line 4 is disconnected When the signal line 4 is disconnected, the control circuit CTL causes the DC-
It becomes impossible to input the output voltage FB of the DC converter (DC-DC CONVERTER). At this time,
No voltage is applied to the division resistors R2 / R3 of the control circuit CTL. As a result, the value of the signal output from the dividing resistors R2 / R3 becomes smaller than the target voltage Vref.

When the signal value output from the dividing resistors R2 / R3 becomes smaller than the target voltage Vref, the error amplifier ERA1 outputs a signal value indicating a negative value. At this time, the value output from the error amplifier ERA1 is smaller than the triangular wave oscillated from the triangular wave oscillator 8.

When the signal value from the error amplifier ERA1 becomes smaller than the triangular wave from the triangular wave oscillator 8, the PWM comparator 9 outputs a high level signal. The high level signal output from the PWM comparator 9 is input to the AND circuit AND1.

On the other hand, a DC-DC converter (DC-DC
Since the output voltage of CONVERTER) is sufficiently smaller than the reference voltage e3 of the power supply e3, the voltage comparator IC2 is
Outputs an ow level signal.

The low-level signal output from the voltage comparator IC2 is the flip-flop FF of the control circuit CTL.
Is input to the set terminal S of. At this time, the voltage comparator I
The inverting output terminal * Q of C2 outputs a high level signal. The high-level signal output from the inverting output terminal * Q of the flip-flop FF is the AND circuit AND
Input to 1.

In this way, the AND circuit AND1
The high level signal from the PWM comparator 9 and the high level signal from the flip-flop FF are input. At this time, the AND circuit AND1 is
It outputs an h-level signal. The High level signal output from the AND circuit AND1 is the drive-1 (1
0) is input.

The drive-1 (10) to which the high level signal is input supplies the drive power from the charge pump circuit 12 to the main switching transistor Tr1 to turn on the main switching transistor Tr1.

By the way, since the signal line 4 is in a disconnected state, the control circuit CTL is operated by the DC-DC converter (DC).
The control for increasing the output voltage FB as described above is continued while the output voltage FB of (-DC CONVERTER) cannot be recognized. As a result, DC-
The actual output voltage of the DC converter (DC-DC CONVERTER) may increase and an overvoltage state may occur.

DC-DC converter (DC-DC CON
When the output voltage of (VERTER) falls into the overvoltage state, the output voltage becomes higher than the reference voltage e3, so that the voltage comparator IC2 outputs a high level signal. The high-level signal output from the voltage comparator IC2 is input to the set terminal S of the flip-flop FF of the control circuit CTL.

The flip-flop FF stores the high-level signal input to the set terminal S. At this time, the non-inverting output terminal Q of the flip-flop FF is Hi
outputs a gh level signal, and the inverting output terminal * Q is Lo
It outputs a w-level signal.

Non-inverting output terminal Q of flip-flop FF
The high level signal output from the OR circuit O
Input to R1. At this time, the OR circuit OR1 outputs a high level signal regardless of the signal from the synchronous live current control circuit 13. The high-level signal output from the OR circuit OR1 is the drive-2
It is input in (11).

The drive-2 (11) to which the high level signal is input supplies the drive power from the charge pump circuit 13 to the synchronous rectification transistor Tr2 to turn on the synchronous rectification transistor Tr2.

The low level signal output from the inverting output terminal * Q of the flip-flop FF is input to the AND circuit AND1. At this time, the AND circuit AND
1 outputs a low level signal regardless of the signal from the PWM comparator 9. This AND circuit AN
The low level signal output from D1 is
1 (10) is input.

Drive inputting Low level signal
1 (10) is the main switching transistor Tr1
The power supply to the main switching transistor Tr1 is stopped and the main switching transistor Tr1 is turned off.

As described above, the DC-DC converter (DC-
When the output voltage of DC CONVERTER) becomes an overvoltage state, the main switching transistor Tr1 is forcibly turned off, and at the same time, the synchronous rectification transistor Tr2 is forcibly turned on.

As a result, the signal line 26, the synchronous rectification transistor Tr2, the signal line 2, the signal line 1, and the choke coil L.
1, the signal line 15, the resistor R1, and the signal line 16 are connected, and a DC-DC converter (DC-DC C
The output voltage of ONVERTER) is clamped to the voltage (0V) of the ground connected to the signal line 26.

Therefore, a DC-DC converter (DC-DC)
It is possible to prevent an overvoltage from being applied to the load of the CONVERTER). Further, the DC-DC converter according to the present embodiment (DC-DC CONVERTE
According to R), it is not necessary to use an organic capacitor having a high withstand voltage as the smoothing capacitor C1, and a fuse for preventing burnout is unnecessary, and the number of constituent parts is reduced.

Further, since the fuse for preventing the capacitor C1 from being burnt out is no longer necessary, the resistance in the DC-DC converter (DC-DC CONVERTER) is reduced, and the DC-DC converter (DC-DC CONVERT) is reduced.
(ER) conversion efficiency is improved.

(3) Main switching transistor T
When r1 has a short circuit failure When the main switching transistor Tr1 has a short circuit failure, the signal line 14
Since the signal line 1 is connected to the signal line 1, the output voltage of the DC-DC converter (DC-DCCONVERTER) may fall into an overvoltage state.

When the output voltage falls into the overvoltage state due to the short-circuit failure of the main switching transistor Tr1, the output voltage becomes larger than the reference voltage e3, so that the voltage comparator I
C2 will output a high level signal.

At this time, the control circuit CTL controls the synchronous rectification transistor Tr as described in (2) above.
2 is forcibly turned on, and the DC-DC converter (DC
-DC CONVERTER) output voltage clamped to ground level. Accordingly, it is possible to prevent the overvoltage from being applied to the load of the DC-DC converter (DC-DC CONVERTER).

Furthermore, if a fuse is provided in the middle of the signal line 14 connecting the battery and the main switching transistor Tr1, a DC-DC converter (DC-DC C
ONVERTER) is applied to the fuse, the signal line 14, the main switching transistor Tr1, the signal line 1, the signal line 2, and the synchronous rectification transistor Tr.
Shorted via 2. At this time, the fuse is blown by the short circuit current.

As a result, the DC-DC converter (DC-D
The voltage applied to C CONVERTER) is cut off in an extremely short time, and it is possible to prevent the overvoltage from being applied to the load of the DC-DC converter (DC-DC CONVERTER) at an early stage. .

Therefore, according to the DC-DC converter (DC-DC CONVERTER) of this embodiment, when an overvoltage condition occurs, the circuit of the DC-DC converter (DC-DC CONVERTER), and The load can be reliably protected.

According to the DC-DC converter according to this embodiment, it is not necessary to use a high voltage organic capacitor as the smoothing capacitor C1, and a fuse for preventing burnout is unnecessary. Therefore, the number of constituent parts is reduced.

Since the fuse for preventing the burn-out of the smoothing capacitor C1 is no longer necessary, the resistance in the DC-DC converter (DC-DC CONVERTER) is reduced, and the DC-DC converter (DC-DC CONVERT) is reduced.
(ER) conversion efficiency is improved.

<DC-DC converter (DC-DC CO
Other Embodiments of NVERTER> The DC-DC converter (DC-DC CO) according to the first embodiment described above.
NVERTER) includes a voltage comparator IC2 and a power supply e3 separately from the control circuit CTL. These voltage comparator IC2 and power supply e3 are incorporated in the control circuit CTL as shown in FIGS. 3 and 4. May be.

In this case, the signal line 21 is directly connected to the control circuit CTL as shown in FIG. Control circuit CTL
4, the dividing resistor R6 / R7 connected to the signal line 21, the voltage comparator IC2 connected to the dividing resistor R6 / R7, and the power supply e3 connected to the voltage comparator IC2 are shown in FIG. With.

The dividing resistors R6 / R7 are resistors for sensing the voltage input via the signal line 21. The voltage sensed by the dividing resistor R6 / R7 is supplied to the voltage comparator I
It is input to the non-inverting input terminal of C2.

The inverting input terminal of the voltage comparator IC2 is connected to the power supply e3 via the signal line 28. Voltage comparator IC
The output terminal of 2 is connected to the set terminal S of the flip-flop FF via the signal line 29.

When the control circuit CTL is constructed in this way, a DC-DC converter (DC-DCCONVERTE)
When the output voltage of R) becomes the overvoltage state, the output voltage of the overvoltage state is input to the dividing resistors R6 / R7 of the control circuit CTL.

The split resistors R6 / R7 sense the output voltage value in the overvoltage state. The voltage value sensed by the dividing resistors R6 / R7 is input to the non-inverting input terminal of the voltage comparator IC2.

The voltage comparator IC2 is composed of dividing resistors R6 / R7.
The reference voltage e3 from the power supply e3 is subtracted from the voltage value from At this time, since the voltage value from the dividing resistors R6 / R7 becomes larger than the reference voltage e3, the voltage comparator IC2 is
It outputs a high level signal.

High output from the voltage comparator IC2
The level signal is the set terminal S of the flip-flop FF.
Entered in. As a result, the control circuit CTL can perform the same control as in the first embodiment described above.

Therefore, even if the voltage comparator IC2 and the power supply e3 are incorporated in the control circuit CTL, the same effect as that of the first embodiment can be obtained.

<Embodiment 2> FIG. 5 shows the DC of the present invention.
It is a figure which shows 2nd Embodiment of a direct-current converter (DC-DC CONVERTER). In the figure, the same names and reference numerals are added to the same components as those in the first embodiment.

DC-DC converter (DC-DC CON
VERTER) is a device which is provided between a battery (not shown) as a power source and a load and which supplies a constant voltage to the load.

(DC-DC converter (DC-DC CO
Configuration of NVERTER) DC according to the present embodiment
The DC converter (DC-DC CONVERTER) is
Fuse F1, control circuit CTL, main switching transistor Tr1, synchronous rectification transistor Tr2, diode D1, choke coil L1, capacitor C1,
A voltage comparator IC1, a power supply e1 for generating a reference voltage e1,
The capacitor C2 and the capacitor C3 are provided.

(DC-DC converter (DC-DC CO
NVERTER) circuit connection form) where:
The connection form of the above components will be described.

The fuse F1 is provided in the middle of the signal line 14 connecting the battery and the main switching transistor Tr1. The main switching transistor Tr1 connected to the battery via the signal line 14 is connected to the choke coil L1 via the signal line 1 and also connected to the control circuit CTL via the signal line 24.

The above main switching transistor T
r1 is, for example, a MOS-FET (Met) having three terminals of a source terminal, a drain terminal, and a gate terminal.
alOxide Semiconductor Fie
ld Effect Transistor).
In this case, the signal line 14 is connected to the drain terminal of the main switching transistor Tr1. Also,
The signal line 1 is the main switching transistor T
It is connected to the source terminal of r1. Further, the signal line 24 is connected to the gate terminal of the main switching transistor Tr1.

The choke coil L1 connected to the main switching transistor Tr1 via the signal line 1 is further connected to a load (not shown) via the signal line 15.
Four signal lines 31, 17, 18, and 19 are connected in the middle of the signal line 14 connecting the fuse F1 and the main switching transistor Tr1.

The above four signal lines 31, 17, 18, 1
The signal line 31 of the 9 near the fuse F1 is connected to the ground via the capacitor C3. The signal line 17 of the four signal lines 31, 17, 18, and 19 is connected to the voltage comparator IC1. This voltage comparator IC1
Has a non-inverting input terminal, an inverting input terminal, and an output terminal, for example. In this case, the signal line 17 is connected to the non-inverting input terminal of the voltage comparator IC1. The inverting input terminal of the voltage comparator IC1 is connected to the power supply e1 via the signal line 22. Further, the output terminal of the voltage comparator IC1 is connected to the control circuit CTL via the signal line 23.

The above four signal lines 31, 17, 18, 1
The signal line 18 of 9 is connected to the control circuit CTL. A signal line 18a is connected in the middle of the signal line 18. The signal line 18a is connected to the ground via the capacitor C2.

The above four signal lines 31, 17, 18, 1
A signal line 19 near the main switching transistor Tr1 of 9 is connected to the control circuit CTL. Also,
Two signal lines 2 and 3 are connected in the middle of the signal line 1 connecting the main switching transistor Tr1 and the choke coil L1.

Of the above two signal lines 2 and 3, the signal line 2 near the main switching transistor Tr1 is connected to the synchronous rectification transistor Tr2. The synchronous rectification transistor Tr2 is connected to the control circuit CTL via the signal line 25 and is also connected to the ground via the signal line 26.

The above-mentioned synchronous rectification transistor Tr2 is
For example, a MOS-FET (Metal Oxid) having three terminals of a drain terminal, a source terminal, and a gate terminal.
eSemiconductor FET). In this case, the signal line 2 is connected to the synchronous rectification transistor Tr.
2 drain terminal. In addition, the above-mentioned signal line 2
5 is connected to the gate terminal of the synchronous rectification transistor Tr2. Further, the signal line 26 is connected to the source terminal of the synchronous rectification transistor Tr2.

Of the above-mentioned two signal lines 2 and 3, the signal line 3 near the choke coil L1 is connected to the cathode terminal of the diode D1. The anode terminal of the diode D1 is connected to the ground via the signal line 27.

Two signal lines 4 and 5 are connected in the middle of the signal line 15 connecting the choke coil L1 and the load. Of the above two signal lines 4 and 5, the signal line 4 near the choke coil L1 is connected to the control circuit CTL.
This signal line 4 is a DC-DC converter (DC-DCCO).
NVERTER) output voltage FB is a signal line for feeding back to the control circuit CTL.

Of the above two signal lines 4 and 5, the signal line 5 near the load is connected to the ground via the capacitor C1. (DC-DC converter (DC-DC CON
Functions of Circuits Constituting VERTER) Next, the functions of the above-described respective constituent elements will be described.

(Capacitor C3) The capacitor C3 is an organic capacitor, and is a DC-DC converter (DC-DC).
This is a smoothing capacitor that removes the pulsating component contained in the voltage input to the CONVERTER).

(Power Supply e1) The power supply e1 generates a reference voltage e1 which is a voltage to be input to the DC-DC converter.

(Voltage Comparator IC1) Voltage Comparator IC1
Is the voltage Vi from the battery and the reference voltage e1 from the power source e1.
Are compared, and a signal OV indicating the comparison result is output.
The signal OV output from the voltage comparator IC1 is supplied to the signal line 2
3 is input to the control circuit CTL.

For example, the voltage comparator IC1 subtracts the reference voltage e1 from the above voltage Vi, and the subtraction result is "0".
In the following cases, a Low level signal is output, and when the subtraction result is a positive value, a High level signal is output.

(Capacitor C2) The capacitor C2 stores electric power for driving the main switching transistor Tr1 and the synchronous rectification transistor Tr2 in an emergency.

(Main switching transistor Tr
1) The main switching transistor Tr1 receives the control signal DH from the control circuit CTL, and the input signal D
According to H, the signal line 14 and the signal line 1 are connected or disconnected.

For example, the main switching transistor Tr1 is turned on when a voltage from the control circuit CTL is applied to its gate terminal, connects the drain terminal and the source terminal, and connects the signal line 14 and the signal line 1. Connect between and.

Further, the main switching transistor T
r1 is turned off unless the voltage from the control circuit CTL is applied to the gate terminal, disconnects the drain terminal and the source terminal, and disconnects the signal line 14 and the signal line 1.

(Choke coil L1) Choke coil L
Reference numeral 1 is a coil for voltage conversion. (Diode D1)
The diode D1 is the main switching transistor T
It is a freewheel diode that releases the energy stored in the choke coil L1 to the output side when r1 is in the off state.

(Synchronous Rectification Transistor Tr2) The synchronous rectification transistor Tr2 receives the signal DL from the control circuit CTL and connects or disconnects the signal line 2 and the signal line 26 in accordance with the input signal DL. Is.

For example, the synchronous rectification transistor Tr2
Is turned on when a voltage from the control circuit CTL is applied to the gate terminal, connects the drain terminal and the source terminal, and connects the signal line 2 and the signal line 26.

The synchronous rectification transistor Tr2 is turned off unless a voltage from the control circuit CTL is applied to the gate terminal, disconnects the drain terminal and the source terminal, and connects the signal line 2 and the signal line 26. Disconnect between and.

In this example, the synchronous rectification transistor T
r2 is a switch circuit for a free wheel that outputs the energy accumulated in the choke coil L1 when the main switching transistor Tr1 is in the off state.

For example, the synchronous rectification transistor Tr2
Is in an ON state (a state in which the signal line 2 and the signal line 26 are connected) when the voltage applied to the diode D1 is in the forward direction, and is OFF when the voltage applied to the diode D1 is in the reverse direction. The state (the state in which the signal line 2 and the signal line 26 are disconnected) is set. At this time, the voltage drop of the diode D1 is reduced.

(Capacitor C1) The capacitor C1 is a smoothing capacitor for removing the pulsating component contained in the voltage output from the choke coil L1.

(Control Circuit CTL) The control circuit CTL includes
In addition to the signal lines 4, 19, 23, 18, 24, 25 described above, an on command value or off command value from the outside and a target voltage Vref from the outside are input. The target voltage Vref from the outside is a DC-DC converter (DC-DC).
CONVERTER) is a reference voltage of a voltage to be output.

The control circuit CTL receives the signal OV from the voltage comparator IC1 and the output voltage FB input via the signal line 4.
According to the target voltage Vref from the outside, the main switching transistor Tr1 and the synchronous rectification transistor Tr2 are switched between the ON state and the OFF state.

Here, the internal structure of the control circuit CTL will be described with reference to FIG. (Structure of Control Circuit CTL) As shown in FIG. 6, the control circuit CTL is a circuit that adopts a pulse width modulation method (PWM method), and includes a power supply 7, a triangular wave oscillator 8, a PWM comparator 9, and a charge pump circuit 12. , Synchronous rectification control circuit 13,
Flip-flop FF, drive-1 (10), and
A drive-2 (11) is provided. Further, the control circuit CTL includes the dividing resistors R2 / R3 and the error amplifier ERA.
1, an OR circuit OR1 and an OR circuit OR2.

(Power Supply 7) The power supply 7 supplies operating power to the circuits forming the control circuit CTL when an ON command value is input from the outside. Further, the power supply 7 stops the supply of operating power to the circuits forming the control circuit CTL when an OFF command value from the outside is input.

(Triangular Wave Oscillator 8) The triangular wave oscillator 8 oscillates a converting triangular wave for converting a voltage into a pulse width at a constant frequency. The triangular wave oscillated from the triangular wave oscillator 8 is input to the PWM comparator 9.

(Dividing resistor R2 / R3) Dividing resistor R2 / R
Reference numeral 3 is connected to the signal line 4 and is adapted to input the output voltage FB of the DC-DC converter (DC-DC CONVERTER). This dividing resistor R2 / R3
Is a sense resistor for sensing the voltage value of the output voltage FB.

The voltage value sensed by the dividing resistor R2 / R3 is input to the error amplifier ERA1. (Error Amplifier ERA1) The error amplifier ERA1 has a voltage value FB sensed by the dividing resistors R2 / R3,
This is an error amplification circuit that inputs a target voltage Vref from the outside and amplifies an error between these voltage values FB and the target voltage Vref. The error amplified by the error amplifier ERA1 is input to the non-inverting input terminal of the PWM comparator 9.

(PWM Comparator 9) The PWM comparator 9 is a voltage comparator having an inverting input terminal and a non-inverting input terminal. The inverting input terminal of the PWM comparator 9 is the triangular wave oscillator 8
Input the conversion triangular wave output from. Also, PWM
The signal output from the error amplifier ERA is input to the non-inverting input terminal of the comparator 9.

The PWM comparator 9 compares the signal input to the non-inverting input terminal with the signal input to the inverting input terminal. For example, the PWM comparator 9 subtracts the signal input to the inverting input terminal from the signal input to the non-inverting input terminal. The PWM comparator 9 keeps the High level while the value obtained by the subtraction shows a negative value (while the signal output from the triangular wave oscillator 8 is larger than the signal output from the error amplifier ERA1). Output a signal.

The PWM comparator 9 keeps the Low level while the value obtained by the subtraction shows a positive value (while the signal output from the triangular wave oscillator 8 is smaller than the signal output from the error amplifier ERA1). The signal of is output.

The signal output from the PWM comparator 9 (Hi
gh level signal or Low level signal)
Is input to the OR circuit OR2 and the synchronous rectification control circuit 13.

(Charge Pump Circuit 12) The charge pump circuit 12 includes the main switching transistor Tr1.
Is supplied to the drive-1 (10) and the voltage for driving the synchronous rectification transistor Tr2 is driven-
2 (11).

(Synchronous Rectification Control Circuit 13) The synchronous rectification control circuit 13 inputs the signal output from the PWM comparator 9. The synchronous rectification control circuit 13 switches the synchronous rectification transistor Tr2 between an on state and an off state in accordance with a signal from the PWM comparator 9 to perform synchronous rectification.

For example, the synchronous rectification control circuit 13 uses the PWM
When the low level signal from the comparator 8 is input, H
It outputs a high level signal. On the other hand, the synchronous rectification control circuit 13 outputs a low level signal when the high level signal from the PWM comparator 8 is input.

The signal output from the synchronous rectification control circuit 13 is input to the OR circuit OR1. (Flip-Flop FF) The flip-flop FF has two input terminals, a set terminal S and a reset terminal R, and an output terminal Q. The signal OV output from the voltage comparator IC1 is input to the set terminal S of the flip-flop FF. At this time, the flip-flop FF is
The signal input to the set terminal S is stored.

Reset terminal R of flip-flop FF
Inputs an ON command value or an OFF command value from the outside. When the ON command value or the OFF command value is input to the reset terminal R, the signal stored in the flip-flop FF is reset to the Low level signal.

The output terminal Q of the flip-flop FF is connected to the OR circuit OR1 and the OR circuit OR2. The output terminal Q outputs the signal stored in the flip-flop FF.

For example, a DC-DC converter (DC-DC
CONVERTER) input voltage Vi is reference voltage e1
In the following cases, the set terminal S of the flip-flop FF inputs a low level signal as the signal OV from the voltage comparator IC1. In this case, the flip-flop F
F stores the low-level signal input to the set terminal S, and the output terminal Q has a flip-flop F.
A low level signal stored in F will be output.

On the other hand, a DC-DC converter (DC-DC
If the input voltage Vi of the CONVERTER exceeds the reference voltage e1 (if the input voltage Vi becomes an overvoltage),
The set terminal S of the flip-flop FF has a voltage comparator I
A high level signal is input as the signal OV from C1.

In this case, the flip-flop FF stores the high-level signal input to the set terminal S, and the output terminal Q outputs the high-level signal stored by the flip-flop FF. Become.

(OR circuit OR2) OR circuit OR2
Is the signal from the PWM comparator 9 and the flip-flop FF
An OR operation is performed with the signal from and the signal indicating the operation result is input to the drive-1 (10).

For example, a DC-DC converter (DC-DC
CONVERTER) input voltage Vi is reference voltage e1
In the following cases, the OR circuit OR2 inputs the low level signal from the output terminal Q of the flip-flop FF. In this case, the OR circuit OR2
The signal from the M comparator 9 is output as it is.

As a result, the DC-DC converter (DC-D
When the input voltage of C CONVERTER) is equal to or lower than the reference voltage e1, the drive-1 (10) outputs the PWM comparator 9
It will operate according to the signal from.

On the other hand, a DC-DC converter (DC-DC
When the input voltage of CONVERTER) is higher than the reference voltage e1 (when the input voltage is in an overvoltage state)
Means that the OR circuit OR2 inputs the high level signal from the output terminal Q of the flip-flop FF.

In this case, the OR circuit OR2 outputs a high level signal regardless of the signal from the PWM comparator 9. As a result, when the input voltage of the DC-DC converter (DC-DC CONVERTER) is in the overvoltage state, the drive-1 (10) outputs PW.
The flip-flop F regardless of the signal from the M comparator 9.
It operates according to the signal from F.

(OR circuit OR1) OR circuit OR1
Performs a logical sum operation of the signal output from the synchronous rectification control circuit 13 and the signal output from the flip-flop FF, and outputs a signal indicating the operation result. The signal output from the OR circuit OR1 is the drive-2 (1
Input to 1).

For example, a DC-DC converter (DC-DC
CONVERTER) input voltage Vi is reference voltage e1
In the following cases, the OR circuit OR1 inputs the low level signal from the flip-flop FF.
In this case, the OR circuit OR1 is the synchronous rectification control circuit 13
The signal from will be output as it is. As a result,
When the input voltage Vi is equal to or lower than the reference voltage e1, the drive-
1 (10) operates according to the signal from the synchronous rectification control circuit 13.

On the other hand, a DC-DC converter (DC-DC
When the input voltage Vi of CONVERTER) becomes larger than the reference voltage e1 (when the input voltage Vi becomes an overvoltage), the OR circuit OR1 inputs the high-level signal from the flip-flop FF.

In this case, the OR circuit OR1 outputs a high level signal regardless of the signal from the synchronous rectification control circuit 13. That is, when the input voltage of the DC-DC converter (DC-DC CONVERTER) becomes an overvoltage, the drive-2 (11) outputs High from the flip-flop FF regardless of the signal from the synchronous rectification control circuit 13. It will operate according to the level signal.

(Drive-1 (10)) Drive-1
(10) switches the main switching transistor Tr1 between the on state and the off state according to the signal from the OR circuit OR2.

For example, the drive-1 (10) supplies the electric power supplied from the charge pump circuit 12 to the main switching transistor Tr1 when the high level signal from the OR circuit OR2 is input to the main switching transistor Tr1. The transistor Tr1 is turned on.

On the other hand, the drive-1 (10) receives the Low level signal from the OR circuit OR2,
The power supply to the main switching transistor Tr1 is stopped and the main switching transistor Tr1
To turn off.

(Drive-2 (11)) Drive-2
(11) switches the synchronous rectification transistor Tr2 between the on state and the off state according to the signal from the OR circuit OR1.

For example, the drive-2 (11) supplies the electric power supplied from the charge pump circuit 12 to the synchronous rectification transistor Tr2 when the high level signal from the OR circuit OR1 is input to the synchronous rectification transistor Tr2. The rectifying transistor Tr2 is turned on.

On the other hand, the drive-2 (11), when the Low level signal from the OR circuit OR1 is input,
The power supply to the synchronous rectification transistor Tr2 is stopped and the synchronous rectification transistor Tr2 is turned off. (Operation / Effect of Second Embodiment) Hereinafter, the DC-DC converter according to the present embodiment (DC-DC CONVERT)
The action and effect of ER) will be described.

(1) DC-DC converter (DC-DC
CONVERTER) is operating normally DC-
When the direct-current converter (DC-DC CONVERTER) is operating normally, that is, when the input voltage Vi of the direct-current converter (DC-DC CONVERTER) shows a normal voltage value, the input voltage Vi Is sufficiently smaller than the reference voltage e1, the voltage comparator IC1
Signal OV from is a signal indicating a low level.

In this case, the low-level signal output from the voltage comparator IC1 is input to the set terminal S of the flip-flop FF of the control circuit CTL. The flip-flop FF stores the input Low level signal.

When the flip-flop FF stores the low-level signal, the low-level signal is output from the output terminal Q of the flip-flop FF. The low-level signal output from the output terminal Q of the flip-flop FF is input to the OR circuit OR2 and the OR circuit OR1 of the control circuit CTL.

Further, the division resistor R2 / R of the control circuit CTL
3 is a DC-DC converter (DC-
Input the output voltage FB of DC CONVERTER. The dividing resistors R2 / R3 sense the input output voltage FB and input the sensed voltage value to the error amplifier ERA1.

The error amplifier ERA1 to which the voltage value from the dividing resistor R2 / R3 is input amplifies and outputs the error between the voltage value from the dividing resistor R2 / R3 and the external target voltage Vref. The error output from the error amplifier ERA1 is input to the PWM comparator 9.

The PWM comparator 9 includes the error amplifier ERA1.
While inputting the error from, the conversion triangular wave from the triangular wave oscillator 8 is input. When the error from the error amplifier ERA1 is smaller than the converting triangular wave from the triangular wave oscillator 8, the PWM comparator 9 outputs a high level signal.

On the other hand, the PWM comparator 9 includes the error amplifier E
When the error from RA1 is larger than the conversion triangular wave from the triangular wave oscillator 8, a Low level signal is output. PW
The signal output from the M comparator 9 is input to the OR circuit OR2 and the synchronous rectification control circuit 13.

In the synchronous rectification control circuit 13 to which the signal from the PWM comparator 9 is input, the signal from the PWM comparator 9 is Hi.
When it is a gh level signal, it outputs a low level signal, and when the signal from the PWM comparator 9 is a low level signal, it outputs a high level signal. The signal output from the synchronous rectification control circuit 13 is the OR circuit OR.
Input to 1.

In this way, the OR circuit OR2 receives the low level signal from the flip-flop FF and PW.
The signal from the M comparator 9 (high level signal or low level signal) is input, and the OR circuit OR1 outputs the low signal from the flip-flop FF.
Level signal and the signal from the synchronous rectification control circuit 13 (H
high level signal or low level signal)
And will be entered.

The OR circuit OR2 is a flip-flop F.
Since the low level signal from F is input, PW
The signal from the M comparator 9 is output as it is.
For example, the OR circuit OR2 is the H from the PWM comparator 9.
When a high level signal is input, a high level signal is output. On the other hand, the OR circuit OR2 outputs the low level signal when the low level signal from the PWM comparator 9 is input. The signal output from the OR circuit OR2 is input to the drive-1 (10).

The drive-1 (10) to which the signal from the OR circuit OR2 is input stops the power supply to the main switching transistor Tr1 if the signal from the OR circuit OR2 is a low level signal.

In this case, the main switching transistor Tr1 is turned off and the signal line 14 and the signal line 1 are disconnected. On the other hand, drive-1 (1
0) supplies the power from the charge pump circuit 12 to the main switching transistor Tr1 if the signal from the OR circuit OR2 is a high level signal.

In this case, the main switching transistor Tr1 is turned on, and the signal line 14 and the signal line 1 are connected. The OR circuit OR1 to which the Low level signal from the flip-flop FF and the signal from the synchronous rectification control circuit 13 are input, receives the signal (High level signal or Low level signal) from the synchronous rectification control circuit 13. It will be output as is. OR circuit OR
The signal output from 1 is input to the drive-2 (11).

The drive-2 (11) to which the signal from the OR circuit OR1 is input stops the power supply to the synchronous rectification transistor Tr2 if the signal from the OR circuit OR1 is a low level signal. At this time, the synchronous rectification transistor Tr2 is turned off, and the signal line 2 and the signal line 26 are disconnected.

On the other hand, in the drive-2 (11), if the signal from the OR circuit OR1 is a high level signal,
The power from the charge pump circuit 12 is supplied to the synchronous rectification transistor Tr2. At this time, the synchronous rectification transistor Tr2 is turned on, and the signal line 2 and the signal line 26 are
And are connected.

(2) DC-DC converter (DC-DC
When the input voltage of the CONVERTER goes into an overvoltage state DC-DC CONVERT
When the voltage input to (ER) becomes an overvoltage, the input voltage Vi becomes higher than the reference voltage e1, so the signal OV from the voltage comparator IC1 becomes a signal indicating a high level.

High output from the voltage comparator IC1
The level signal is the flip-flop F of the control circuit CTL.
It is input to the set terminal S of F. At this time, the flip-flop FF stores the high-level signal input to the set terminal S. And the flip-flop FF
Outputs the stored high-level signal from the output terminal Q.

Hi output from the flip-flop FF
The gh level signal is the OR circuit OR of the control circuit CTL.
2 and the OR circuit OR1. Further, the dividing resistors R2 / R3 of the control circuit CTL are connected via the signal line 4 to a DC-DC converter (DC-DC CONVERTER).
Input the output voltage FB of. And the division resistance R2 / R
3 senses the input output voltage FB and inputs the sensed voltage value to the error amplifier ERA1.

The error amplifier ERA1 to which the voltage value from the dividing resistor R2 / R3 is input amplifies and outputs the error between the voltage value from the dividing resistor R2 / R3 and the target voltage Vref from the outside. The error output from the error amplifier ERA1 is input to the PWM comparator 9.

The PWM comparator 9 includes the error amplifier ERA1.
While inputting the error from, the conversion triangular wave from the triangular wave oscillator 8 is input. At that time, when the error from the error amplifier ERA1 is smaller than the converting triangular wave from the triangular wave oscillator 8, the PWM comparator 9 outputs a high level signal.

On the other hand, the PWM comparator 9 uses the error amplifier E
When the error from RA1 is larger than the conversion triangular wave from the triangular wave oscillator 8, a Low level signal is output. PW
The signal output from the M comparator 9 is input to the OR circuit OR2 and the synchronous rectification control circuit 13.

In the synchronous rectification control circuit 13 to which the signal from the PWM comparator 9 is input, the signal from the PWM comparator 9 is Hi.
When it is a gh level signal, a Low level signal is output.

On the other hand, the signal from the PWM comparator 9 is Low.
When it is a level signal, the synchronous rectification control circuit 13
It outputs a high level signal. The signal output from the synchronous rectification control circuit 13 is input to the OR circuit OR1.

In this way, the OR circuit OR2 receives the PW signal from the high level signal from the flip-flop FF.
The signal (high level signal or low level signal) from the M comparator 9 is input.

The OR circuit OR1 is a flip-flop F
High level signal from F and synchronous rectification control circuit 1
Signal from 3 (High level signal or Lo
w level signal).

In this case, since the OR circuit OR2 inputs the high level signal from the flip-flop FF, it is high regardless of the signal from the PWM comparator 9.
Output level signal.

High output from the OR circuit OR2
The level signal is input to the drive-1 (10).
The drive-1 (10) to which the High level signal from the OR circuit OR2 is input supplies the power from the charge pump circuit 12 to the main switching transistor Tr1. At this time, the main switching transistor T
r1 is turned on, and the signal line 14 and the signal line 1 are connected.

On the other hand, since the OR circuit OR1 inputs the high level signal from the flip-flop FF, it is related to the signal from the synchronous rectification control circuit 13 (high level signal or low level signal). Without H
A high level signal will be output.

High output from the OR circuit OR1
The level signal is input to the drive-2 (11).
The drive-2 (11) to which the high-level signal from the OR circuit OR1 is input supplies the power from the charge pump circuit 12 to the synchronous rectification transistor Tr2.
At this time, the synchronous rectification transistor Tr2 is turned on, and the signal line 2 and the signal line 26 are connected.

When the main switching transistor Tr1 and the synchronous rectification transistor Tr2 are turned on,
The current from the battery is the fuse F1, the signal line 14, the main switching transistor Tr1, the signal line 1, the signal line 2, the synchronous rectification transistor Tr2, and the signal line 26.
Through to the ground. At this time, an excessive current flows through the fuse F1, and the fuse F1 is blown.

Therefore, since the fuse F1 is blown, the DC-DC CONVERTER (DC-DC CONVERTER).
TER) components, especially DC-DC converters (DC
It is possible to prevent an excessive voltage from being applied to the capacitor C3 provided in the input part of (-DC CONVERTER), and to prevent the capacitor C3 from burning.

Further, in the DC-DC converter according to the present embodiment, the power source of the control circuit CTL is the main switching transistor Tr.
1 and the synchronous rectification transistor Tr2 cannot be generated, the main switching transistor Tr1 and the synchronous rectification transistor Tr2 are driven by the electric power accumulated in the capacitor C2. Thereby, a DC-DC converter (DC-DC CONVERT
ER) can guarantee the operation of the main switching transistor Tr1 and the synchronous rectification transistor Tr2 until the fuse F1 is blown.

The main switching transistor Tr
It goes without saying that the driving power supply for the 1 and the synchronous rectification transistor Tr2 is not limited to the capacitor C2. Also,
DC-DC converter according to the present embodiment (DC-DC
According to the CONVERTER), it is not necessary to use a high voltage organic capacitor as the capacitor C3, a fuse for preventing burnout is not required, and the number of components is reduced.

Further, since the fuse for preventing the capacitor C3 from being burnt out is unnecessary, the resistance in the DC-DC converter (DC-DC CONVERTER) is reduced, and the DC-DC converter (DC-DC CONVERT) is reduced.
(ER) conversion efficiency is improved.

<DC-DC converter (DC-DC CO
Other Embodiment of NVERTER> DC-DC converter (DC-DC CO) according to the second embodiment described above.
NVERTER), the voltage comparator IC1 and the power supply e1 are provided separately from the control circuit CTL. However, as shown in FIGS. 7 and 8, the voltage comparator IC1 and the power supply e1 are provided in the control circuit CTL. Good.

In this case, the signal line 17 is connected to the control circuit CTL.
Will be directly connected with. Then, the control circuit CTL
In, the voltage Vi input via the signal line 17 is input to the dividing resistors R4 / R5.

The dividing resistors R4 / R5 are resistors for sensing the voltage Vi input via the signal line 17. The voltage Vi sensed by the dividing resistors R4 / R5 is input to the non-inverting input terminal of the voltage comparator IC1.

The inverting input terminal of the voltage comparator IC1 is connected to the power source e1 via the signal line 22. Further, the output terminal of the voltage comparator IC1 is connected to the set terminal S of the flip-flop FF via the signal line 23.

In the case where the control circuit CTL is configured as described above, when the voltage Vi from the battery is in the overvoltage state, the voltage Vi in this overvoltage state causes the division resistance R4 / of the control circuit CTL.
Input to R5.

The dividing resistors R4 / R5 sense the voltage value of the voltage Vi in the overvoltage state. The voltage value sensed by the dividing resistors R4 / R5 is input to the non-inverting input terminal of the voltage comparator IC1.

The voltage comparator IC1 is composed of dividing resistors R4 / R5.
The reference voltage from the power source e1 is subtracted from the voltage value from.
At this time, since the voltage value from the dividing resistors R4 / R5 becomes larger than the reference voltage, the voltage comparator IC1 outputs a high level signal.

As a result, the High level signal output from the voltage comparator IC1 is input to the set terminal S of the flip-flop FF. In this way, the voltage comparator IC
1 and the power source e1 can be incorporated in the control circuit CTL, the same effect as that of the second embodiment can be obtained.

Further, in the examples shown in FIGS. 7 and 8, the control circuit CTL has a built-in power source e2 for generating the target voltage Vref. As described above, if the configuration shown in FIGS. 7 and 8 is adopted, the same effect as that of the second embodiment described above can be obtained, and the DC-DC converter (DC-DC) can be obtained.
The circuit configuration of the CONVERTER) can be simplified.

<Third Embodiment> FIG. 9 shows a DC-DC converter according to the present invention.
It is a figure which shows 3rd Embodiment of R). In the figure, the same components as those of the first and second embodiments described above are designated by the same names and reference numerals.

(DC-DC converter (DC-DC CO
Configuration of NVERTER) DC-DC converter (DC-
DC CONVERTER) is a fuse F1, a voltage comparator IC1, a power supply e1, a capacitor C3, a capacitor C
2, OR circuit OR3, control circuit CTL, main switching transistor Tr1, synchronous rectification transistor T
r2, diode D1, choke coil L1, resistance R
1, capacitor C1, voltage comparator IC2, and power supply e
Equipped with 3.

(DC-DC converter (DC-DC CO
NVERTER) circuit connection form) where:
The connection form of the above components will be described.

The fuse F1 is provided in the middle of the signal line 14 connecting the battery and the main switching transistor Tr1. The main switching transistor Tr1 connected to the battery via the signal line 14 is connected to the choke coil L1 via the signal line 1 and, at the same time, connected to the signal line 2
4 is connected to the control circuit CTL.

The choke coil L1 connected to the main switching transistor Tr1 via the signal line 1 is further connected to the resistor R1 via the signal line 15. Resistor R1 connected to choke coil L1 via signal line 15
Is connected to the load via the signal line 16.

Further, four signal lines 31, 17, 18, 19 are connected in the middle of the signal line 14 connecting the fuse F1 and the main switching transistor Tr1.

The above-mentioned four signal lines 31, 17, 18, 1
The signal line 31 of the 9 near the fuse F1 is connected to the ground via the capacitor C3. The signal line 17 of the four signal lines 31, 17, 18, and 19 is connected to the voltage comparator IC1. This voltage comparator IC1
Has a non-inverting input terminal, an inverting input terminal, and an output terminal, for example. In this case, the signal line 17 is connected to the non-inverting input terminal of the voltage comparator IC1. The inverting input terminal of the voltage comparator IC1 is connected to the power supply e1 via the signal line 22. Further, the output terminal of the voltage comparator IC1 is connected to the OR circuit OR3 via the signal line 23.

The above-mentioned four signal lines 31, 17, 18, 1
The signal line 18 of 9 is connected to the control circuit CTL. A signal line 18a is connected in the middle of the signal line 18. The signal line 18a is connected to the ground via the capacitor C2.

The above-mentioned four signal lines 31, 17, 18, 1
A signal line 19 near the main switching transistor Tr1 of 9 is connected to the control circuit CTL. Also,
Two signal lines 2 and 3 are connected in the middle of the signal line 1 connecting the main switching transistor Tr1 and the choke coil L1.

Of the above two signal lines 2 and 3, the signal line 2 near the main switching transistor Tr1 is connected to the synchronous rectification transistor Tr2. The synchronous rectification transistor Tr2 is connected to the control circuit CTL via the signal line 25 and at the same time connected to the ground via the signal line 26.

Of the two signal lines 2 and 3 described above, the signal line 3 near the choke coil L1 is connected to the cathode terminal of the diode D1. The anode terminal of the diode D1 is connected to the ground via the signal line 27.

Further, one signal line 20 is connected in the middle of the signal line 15 connecting the choke coil L1 and the resistor R1. The signal line 20 is connected to the control circuit CTL, and is a DC-DC converter (DC-DC CO).
NVERTER) is a signal line for inputting the voltage value CS output from the control circuit CTL.

Also, three signal lines 4, 5, 21 are connected in the middle of the signal line 16 connecting the resistor R1 and the load. Of the three signal lines 4, 5, and 21, the signal line 4 near the resistor R1 is connected to the control circuit CTL. The signal line 4 is a DC-DC converter (DC-DC CONV).
The voltage value FB output from the control circuit CT
It is a signal line for feeding back to L.

Of the three signal lines 4, 5, and 21, the middle signal line 5 is connected to the ground via the smoothing capacitor C1. Of the three signal lines 4, 5, and 21, the signal line 21 near the load is connected to the voltage comparator IC2. The voltage comparator IC2 is, for example, a voltage comparator having a non-inverting input terminal, an inverting input terminal, and an output terminal. In this case, the signal line 21 is connected to the voltage comparator I
It is connected to the non-inverting input terminal of C2. The inverting input terminal of the voltage comparator IC2 is connected to the power supply e3 via the signal line 28. Furthermore, the above voltage comparator IC2
The output terminal of is connected to the OR circuit OR3 via the signal line 29.

Further, as described above, the OR circuit OR3 is connected to the voltage comparator IC1 via the signal line 23 and at the same time connected to the voltage comparator IC2 via the signal line 29. The OR circuit OR3 is a circuit having two input terminals and one output terminal. In this case, the signal lines 23 and 29 are connected to the two input terminals.
And are connected. The output terminal of the OR circuit OR3 is connected to the control circuit CTL via the signal line 30.

As described above, the control circuit CTL is connected to the signal lines 30, 18, 19, 24, 25, 20, and 4 and, at the same time, receives an ON command value or an OFF command value from the outside. The target voltage Vref is input.

(DC-DC converter (DC-DC CO
Function of Circuit Constituting NVERTER) Next, the function of each of the above components will be described. The description of the constituent elements described in the first and second embodiments will be omitted.

(OR circuit OR3) OR circuit OR3
Inputs the signal output from the voltage comparator IC1 and the signal output from the voltage comparator IC2. Then, the OR circuit OR3 includes the voltage comparator IC1 and the voltage comparator IC2.
And a High level signal from at least one of the two, namely, a DC-DC converter (DC-DC).
When the input voltage of the CONVERTER becomes larger than the reference voltage e1, or when the DC-DC converter (D
When the output voltage of (C-DC CONVERTER) becomes larger than the reference voltage e3, a high level signal indicating that an overvoltage state has occurred is output.

Further, the OR circuit OR3 is provided with a voltage comparator I
When a Low level signal is input from both circuits of C1 and the voltage comparator IC2, that is, the input voltage of the DC-DC converter (DC-DC CONVERTER) is equal to or lower than the reference voltage e1, and the DC-DC. Converter (D
When the output voltage of (C-DC CONVERTER) is equal to or lower than the reference voltage e3, a Low level signal is output. (Operation / Effect of Third Embodiment) Hereinafter, the DC-DC converter according to the present embodiment (DC-DC CONVERT).
The action and effect of ER) will be described.

(1) DC-DC converter (DC-DC
CONVERTER) is operating normally DC-
When the direct current converter (DC-DC CONVERTER) is operating normally, that is, the input voltage of the direct current-direct current converter (DC-DC CONVERTER) is the reference voltage e1 or less, and the direct current-direct current converter ( DC
-DCCONVERTER) output voltage is reference voltage e3
In the following cases, the voltage comparator IC1 and the voltage comparator IC
2 means to output a low level signal.

Low level signals output from the voltage comparators IC1 and IC are input to the OR circuit OR3. In this case, the OR circuit OR3 outputs a Low level signal.

The Low level signal output from the OR circuit OR3 is the flip-flop FF of the control circuit CTL.
Is input to the set terminal S of. Then, the flip-flop FF stores the input low-level signal. At this time, the output terminal Q of the flip-flop FF outputs the low-level signal stored in the flip-flop FF.

The low-level signal output from the output terminal Q of the flip-flop FF is input to the OR circuit OR1 and the OR circuit OR2. Flip flop FF
OR circuit OR1 to which the Low level signal from
Outputs the signal (Low level signal or High level signal) from the synchronous rectification control circuit 13 as it is. The signal output from the OR circuit OR1 is input to the drive-2 (11).

Drive-2 (11) is an OR circuit OR
The synchronous rectification transistor Tr2 is switched between the ON state and the OFF state in accordance with the signal from the signal 1, that is, the signal from the synchronous rectification control circuit 13. As a result, drive-2
(11) can turn on the synchronous rectification transistor Tr2 while the main switching transistor Tr1 is in the off state and the diode D1 is releasing the energy stored in the choke coil L1 to the output side. it can.

In addition, Low from the flip-flop FF
The OR circuit OR2 to which the level signal is input is the signal from the PWM comparator 9 (the signal of the Low level or the H level).
(high level signal) is output as it is. The signal output from the OR circuit OR2 is input to the drive-1 (10).

Drive-1 (10) is an OR circuit OR
The main switching transistor Tr1 is switched between the on-state and the off-state according to the signal from 2, that is, the signal from the PWM comparator 9. As a result, drive-
1 (10) turns on the main switching transistor Tr1 when the triangular wave from the triangular wave oscillator 8 is higher than the voltage value from the error amplifier ERA1 so that the triangular wave from the triangular wave oscillator 8 is higher than the voltage value from the error amplifier ERA1. When it is low, the main switching transistor Tr1 can be turned off.

(2) DC-DC converter (DC-DC
When the input voltage of the CONVERTER is in an overvoltage state DC-DC converter (DC-DC CONVERT)
When the voltage input to (ER) becomes an overvoltage, the input voltage becomes larger than the reference voltage e1. Therefore, the voltage comparator I
The signal output from C1 becomes a signal indicating a high level. The High level signal output from the voltage comparator IC1 is input to the OR circuit OR3.

On the other hand, a DC-DC converter (DC-DC
Since the output voltage of CONVERTER) is smaller than the reference voltage e3, the signal output from the voltage comparator IC2 becomes a low level signal. This voltage comparator IC2
The low-level signal output from the OR circuit OR
Input to 3.

In this way, the OR circuit OR3 inputs the high level signal from the voltage comparator IC1 and the low level signal from the voltage comparator IC2. At this time, the signal O output from the OR circuit OR3
V becomes a high level signal. OR circuit OR3
The high level signal output from the control circuit CT
It is input to the L flip-flop FF.

The flip-flop FF to which the high-level signal from the OR circuit OR3 is input is
A gh level signal will be stored. The output terminal Q of the flip-flop FF is
The high level signal stored in F is output.

The High-level signal output from the output terminal Q of the flip-flop FF is input to the OR circuit OR1 and OR2. Flip flop F
OR circuit O to which a high level signal from F is input
R1 outputs a high-level signal regardless of the signal from the synchronous rectification control circuit 13. OR circuit OR
Drive that inputs High level signal from 1-2
(11) supplies the power from the charge pump circuit 12 to the synchronous rectification transistor Tr2. At this time, the synchronous rectification transistor Tr2 is turned on, and the signal line 2 and the signal line 26 are connected.

In addition, the high level from the flip-flop FF
The OR circuit OR2 to which the signal of the h level is input is PWM
A high-level signal is output regardless of the signal from the comparator 9.

High output from the OR circuit OR2
The level signal is input to the drive-1 (10).
The drive-1 (10) to which the High level signal from the OR circuit OR2 is input supplies the power from the charge pump circuit 12 to the main switching transistor Tr1. At this time, the main switching transistor T
r1 is turned on and connects between the signal line 14 and the signal line 1.

As a result, the DC-DC converter (DC-D
The voltage input to (C CONVERTER) is applied to the ground through the fuse F1, the signal line 14, the main switching transistor Tr1, the signal line 1, the signal line 2, the synchronous rectification transistor Tr2, and the signal line 26. At this time, an excessive current flows through the fuse F1, and the fuse F1 is blown.

Therefore, since the fuse F1 is blown, the DC-DC CONVERTER (DC-DC CONVERTER).
TER) components, especially DC-DC converters (DC
It is possible to prevent an excessive voltage from being applied to the capacitor C3 provided in the input part of (-DC CONVERTER), and to prevent the capacitor C3 from burning.

Further, according to the DC-DC converter according to the present embodiment,
It is not necessary to use a high voltage organic capacitor as the capacitor C3, and a fuse for preventing burnout is unnecessary,
The number of components is reduced.

Furthermore, since the fuse for preventing the capacitor C3 from being burnt out is no longer needed, the resistance in the DC-DC converter (DC-DC CONVERTER) is reduced, and the DC-DC converter (DC-DC CONVERT) is reduced.
(ER) conversion efficiency is improved.

(3) DC-DC converter (DC-DC
When the output voltage of the CONVERTER goes into an overvoltage state DC-DC CONVERT
When the output voltage of (ER) becomes an overvoltage state, the output voltage becomes larger than the reference voltage e3, so the voltage comparator IC
2 outputs a high level signal. The high-level signal output from the voltage comparator IC2 is input to the logical sum circuit OR3 via the signal line 29.

On the other hand, a DC-DC converter (DC-DC
Since the input voltage of CONVERTER) is smaller than the reference voltage e1, the voltage comparator IC1 outputs a low level signal. The low-level signal output from the voltage comparator IC1 is input to the OR circuit OR3 via the signal line 23.

The OR circuit OR3 to which the low level signal from the voltage comparator IC1 and the high level signal from the voltage comparator IC3 are input outputs a high level signal. High output from the OR circuit OR3
The h-level signal is input to the control circuit CTL.

At this time, the control circuit CTL forcibly turns on the main switching transistor Tr1 and the synchronous rectification transistor Tr2 as described in (1) above, and the DC-DC converter (DC-DC). C
(ONVERTER) input voltage is conducted to the ground through the fuse F1, the signal line 14, the main switching transistor Tr1, the signal line 1, the signal line 2, the synchronous rectification transistor Tr2, and the signal line 26. At this time, an excessive current flows through the fuse F1, and the fuse F1 is blown.

As a result, the DC-DC converter (DC-D
The voltage input to the C CONVERTER is cut off, and the DC-DC converter (DC-DC CO)
It is possible to prevent an overvoltage from being applied to the load (NVERTER).

Therefore, according to the DC-DC converter according to the present embodiment, the DC-DC converter (DC-DC CONVERT).
ER) output voltage becomes overvoltage, DC-
It is possible to reliably protect the circuit of the DC converter (DC-DC CONVERTER) and the load.

Further, according to the direct current-direct current converter (DC-DC CONVERTER) of the present embodiment,
It is not necessary to use a high withstand voltage organic capacitor as the smoothing capacitor C1, and a fuse for preventing burnout is unnecessary, and the number of constituent parts is reduced.

Further, since the fuse for preventing the burning of the smoothing capacitor C1 is not necessary, the resistance in the DC-DC converter (DC-DC CONVERTER) is reduced, and the DC-DC converter (DC-DC) is reduced. DC CONV
ERTER) conversion efficiency is improved.

<Fourth Embodiment> FIG. 10 shows a DC-DC converter according to the present invention.
It is a figure which shows 4th Embodiment of R). In the figure, the same components and elements as those of the third embodiment are designated by the same names and reference numerals.

(DC-DC converter (DC-DC CO
Configuration of NVERTER) DC-DC converter (DC-
DC CONVERTER) is a fuse F1, a voltage comparator IC1, a power supply e1, a capacitor C3, a capacitor C
2, control circuit CTL, main switching transistor Tr1, synchronous rectification transistor Tr2, diode D
1, choke coil L1, resistor R1, capacitor C1,
It is provided with a voltage comparator IC2 and a power supply e3.

(DC-DC converter (DC-DC CO
NVERTER) circuit connection form) where:
The connection form of the above components will be described. It should be noted that, here, only the connection form different from the third embodiment will be described.

The output terminal of the voltage comparator IC1 is the signal line 2
3 is directly connected to the control circuit CTL. In this case, the signal OV1 output from the voltage comparator IC1 is input to the control circuit CTL via the signal line 23.

The output terminal of the voltage comparator IC2 is directly connected to the control circuit CTL via the signal line 29. In this case, the signal OV2 output from the voltage comparator IC2
Is input to the control circuit CTL via the signal line 29.

The other connection forms are the same as those of the above-mentioned third embodiment. (DC-DC converter (DC-DC
CONVERTER) function of the circuits that make up)
The functions of the above components will be described. The description of the same components as those in the third embodiment will be omitted.

(Control Circuit CTL) The control circuit CTL is connected to the output terminal of the voltage comparator IC1 via the signal line 23 and outputs the signal OV1 output from the voltage comparator IC1.
Enter.

Also, the control circuit CTL is a voltage comparator IC.
The signal OV2 output from the voltage comparator IC2 is input.
In this case, the control circuit CTL uses the DC-DC converter (DC-DC) as the signal OV1 from the voltage comparator IC1.
When a signal (high level signal) indicating that the input voltage of CONVERTER) is in an overvoltage state is input,
The main switching transistor Tr1 and the synchronous rectification transistor Tr2 are forcibly turned on so that the fuse F1 is blown.

Also, the control circuit CTL is a voltage comparator IC.
2 as a signal OV2 from the DC-DC converter (DC
-When a signal (high level signal) indicating that the output voltage of -DC CONVERTER is in an overvoltage state is input, the main switching transistor Tr1 is forcibly turned off and at the same time the synchronous rectification transistor Tr2 is forcibly turned on. The state is set so that the output voltage of the DC-DC CONVERTER is clamped to the ground level.

Here, the control circuit C for realizing the above function
The internal structure of the TL will be described. (Structure of Control Circuit CTL) As shown in FIG. 11, the control circuit CTL includes a power supply 7, a triangular wave oscillator 8, a PWM comparator 9, a charge pump circuit 12, a synchronous rectification control circuit 13,
Flip-flop FF1, flip-flop FF2, drive-1 (10), drive-2 (11), dividing resistors R2 / R3, error amplifiers ERA1 and ERA2, logical product circuit AND1, logical sum circuit OR1, logical sum circuit OR4,
The flip-flop FF1 including the OR circuit OR5 (flip-flop FF1) has two input terminals, a set terminal S and a reset terminal R, and an output terminal Q.
have.

Set terminal S of flip-flop FF1
Receives the signal OV1 from the voltage comparator IC1. When the signal OV1 is input to the set terminal S, the flip-flop FF1 stores the input signal OV1.

The reset terminal R of the flip-flop FF1 receives an on command value or an off command value from the outside. When an ON command value or an OFF command value is input to the reset terminal R, the flip-flop FF1
The stored contents are reset and the Low level signal is stored.

Further, the output terminal Q of the flip-flop FF1 is connected to the OR circuit OR1 and the OR circuit OR4. This output terminal Q is a flip-flop FF
1 outputs the stored signal.

For example, a DC-DC converter (DC-DC
CONVERTER) input voltage is equal to or lower than the reference voltage e1, the set terminal S of the flip-flop FF1.
Inputs a low-level signal as the signal OV1 from the voltage comparator IC1. In this case, the flip-flop F
The F1 stores the low-level signal input to the set terminal S. And the flip-flop FF
The output terminal Q of 1 outputs the low-level signal stored in the flip-flop FF1.

A DC-DC converter (DC-DC)
When the input voltage of CONVERTER) exceeds the reference voltage e1 (when the input voltage becomes an overvoltage), the set terminal S of the flip-flop FF1 inputs a high level signal as the signal OV1 from the voltage comparator IC1. . In this case, the flip-flop FF1 stores the High level signal input to the set terminal S. The output terminal Q of the flip-flop FF1
Outputs the high-level signal stored in the flip-flop FF1.

(Flip-Flop FF2) The flip-flop FF2 has two input terminals, a set terminal and a reset terminal, and two output terminals, a non-inverting output terminal Q and an inverting output terminal * Q.

Set terminal S of flip-flop FF2
Receives the signal OV2 from the voltage comparator IC2. The reset terminal R of the flip-flop FF2 inputs an ON command value or an OFF command value from the outside. When the ON command value or the OFF command value is input to the reset terminal, the signal stored in the flip-flop FF2 becomes Low.
Reset to level signal.

The non-inverting output terminal Q of the flip-flop FF2 is connected to the OR circuit OR5. This output terminal Q
Outputs the signal stored in the flip-flop FF2 as it is.

For example, a DC-DC converter (DC-DC
CONVERTER) output voltage is equal to or lower than the reference voltage e3, the set terminal S of the flip-flop FF2.
Inputs a low-level signal as the signal OV2 from the voltage comparator IC2. In this case, the flip-flop F
F2 will store the Low level signal input to the set terminal S, and the non-inverting output terminal Q will output the Low level signal stored by the flip-flop FF2.

Further, a DC-DC converter (DC-DC
When the output voltage of CONVERTER exceeds the reference voltage e3 (when the output voltage becomes an overvoltage), the set terminal S of the flip-flop FF2 inputs a high-level signal as the signal OV2 from the voltage comparator IC2. . In this case, the flip-flop FF2 has the set terminal S
The high-level signal input to is stored, and the non-inverting output terminal Q outputs the high-level signal stored in the flip-flop FF2.

Inverted output terminal of flip-flop FF2 *
Q is connected to the AND circuit AND1. The inverting output terminal * Q outputs a value obtained by inverting the signal value stored in the flip-flop FF2, that is, a signal obtained by inverting the Low level and the High level.

For example, if the signal OV2 stored in the flip-flop FF2 is a low level signal, the inverting output terminal * Q (DC-DC converter (DC-DC CO
If the output voltage of NVERTER) is equal to or lower than the reference voltage e3), a high level signal is output. If the signal OV2 stored in the flip-flop FF2 is a high level signal, the inverting output terminal * Q (DC-DC CONVERTE
If the output voltage of R) exceeds the reference voltage e3),
A low level signal will be output.

(Logical product circuit AND1) logical product circuit AND
1 inputs the signal output from the PWM comparator 9 and the signal output from the inverting output terminal * Q of the flip-flop FF2. The AND circuit AND1 calculates the logical product of the signal from the PWM comparator 9 and the signal from the flip-flop FF2, and outputs a signal indicating the calculation result.
The signal output from the AND circuit AND1 is input to the OR circuit OR4.

For example, a DC-DC converter (DC-DC
If the output voltage of CONVERTER) is equal to or lower than the reference voltage e3, the AND circuit AND1 outputs the signal from the PWM comparator 9 and the inverting output terminal * Q of the flip-flop FF2.
And a high-level signal from. in this case,
The AND circuit AND1 outputs the signal from the PWM comparator 9 as it is.

In addition, a DC-DC converter (DC-DC
If the output voltage of CONVERTER) becomes larger than the reference voltage e3 (if the output voltage becomes an overvoltage),
The AND circuit AND1 and the signal from the PWM comparator 9
Lo from the inverting output terminal * Q of the flip-flop FF2
The signal of w level is input. In this case, the AND circuit AND1 outputs a low-level signal regardless of the signal from the PWM comparator 9.

(OR circuit OR4) OR circuit OR4
Inputs the signal output from the AND circuit AND1 and the signal output from the output terminal Q of the flip-flop FF1. This logical sum circuit OR4 is a logical product circuit AND
The logical sum of the signal from 1 and the signal from the output terminal Q of the flip-flop FF1 is calculated, and a signal indicating the calculation result is output. The signal output from the OR circuit OR4 is
Input to drive-1 (10).

For example, a DC-DC converter (DC-DC
If the input voltage of CONVERTER is equal to or lower than the reference voltage e1 and the output voltage is equal to or lower than the reference voltage e3, the OR circuit OR4 outputs the signal from the AND circuit AND1 (the signal output from the PWM comparator 9). Same signal as)
And Low from the output terminal Q of the flip-flop FF1
Level signal and will be input. In this case, the OR circuit OR4 outputs the signal from the AND circuit AND1, that is, the signal from the PWM comparator 9 as it is.

DC-DC converter (DC-DC CON
VERTER) input voltage is greater than the reference voltage e1 and the output voltage is less than or equal to the reference voltage e3,
The OR circuit OR4 outputs the signal from the AND circuit AND1 (the same signal as the signal output from the PWM comparator 9).
And High from the output terminal Q of the flip-flop FF1
The signal of the h level is input. In this case, the OR circuit OR4 outputs a high level signal regardless of the signal from the AND circuit AND1.

DC-DC converter (DC-DC CON
VERTER) input voltage is less than or equal to the reference voltage e1
When the output voltage becomes higher than the reference voltage e3, the OR circuit OR4 outputs L from the AND circuit AND1.
The ow signal and the low level signal from the flip-flop FF1 are input. In this case, the OR circuit OR4 outputs a Low level signal.

(OR circuit OR1) OR circuit OR1
Inputs the signal output from the synchronous rectification control circuit 13 and the signal output from the output terminal Q of the flip-flop FF1. Then, the logical sum circuit OR1 calculates the logical sum of the signal from the synchronous rectification control circuit 13 and the signal from the flip-flop FF1, and outputs a signal indicating the calculation result. The signal output from the OR circuit OR1 is input to the OR circuit OR5.

For example, a DC-DC converter (DC-DC
If the input voltage of CONVERTER) is equal to or lower than the reference voltage e1, the OR circuit OR1 outputs the signal from the synchronous rectification control circuit 13 and the Lo from the flip-flop FF1.
The signal of w level is input. In this case, the OR circuit OR1 outputs the signal from the synchronous rectification control circuit 13 as it is.

DC-DC converter (DC-DC CON
(VERTER) input voltage becomes higher than the reference voltage e1, the OR circuit OR1 outputs the signal from the synchronous rectification control circuit 13 and the Hi from the flip-flop FF1.
A gh level signal is input. in this case,
The OR circuit OR1 outputs a high-level signal regardless of the signal from the synchronous rectification control circuit 13.

(OR circuit OR5) OR circuit OR5
Inputs the signal output from the OR circuit OR1 and the signal output from the output terminal Q of the flip-flop FF2. The OR circuit OR5 is the OR circuit OR.
The logical sum of the signal from 1 and the signal from the flip-flop FF2 is calculated, and the calculation result is output. The signal output from the OR circuit OR5 is the drive-2 (1
Input to 1).

For example, a DC-DC converter (DC-DC
If the input voltage of CONVERTER) is equal to or lower than the reference voltage e1 and the output voltage is equal to or lower than the reference voltage e3, the OR circuit OR5 outputs Hi
The gh level signal and the Low level signal from the output terminal Q of the flip-flop FF2 are input. In this case, the OR circuit OR5 outputs a high level signal.

DC-DC converter (DC-DC CON
VERTER) input voltage is greater than the reference voltage e1
When the output voltage is equal to or lower than the reference voltage e3, the OR circuit OR5 inputs the high level signal from the OR circuit OR1 and the low level signal from the output terminal Q of the flip-flop FF2. become. In this case, the OR circuit OR5 outputs a high level signal.

DC-DC converter (DC-DC CON
VERTER) input voltage is less than or equal to the reference voltage e1
When the output voltage becomes higher than the reference voltage e3, the signal from the OR circuit OR1 (the synchronous rectification control circuit 1
3) and the High level signal from the flip-flop FF2. In this case, the OR circuit OR5 outputs a high level signal regardless of the signal from the OR circuit OR1.

(Drive-1 (10)) Drive-1
(10) switches the main switching transistor Tr1 between the on state and the off state according to the signal from the OR circuit OR4.

For example, the drive-1 (10) supplies the power supplied from the charge pump circuit 12 to the main switching transistor Tr1 when the High level signal from the OR circuit OR4 is input to the main switching transistor Tr1. The transistor Tr1 is turned on.

Further, the drive-1 (10) stops the power supply to the main switching transistor Tr1 when the Low level signal from the AND circuit AND1 is inputted, and the main switching transistor T1.
Turn off r1. (Operation / Effect of Fourth Embodiment) Hereinafter, a DC-DC converter according to the present embodiment (DC-DC CONVERT).
The action and effect of ER) will be described.

(1) DC-DC converter (DC-DC
CONVERTER) is operating normally DC-
When the direct current converter (DC-DC CONVERTER) is operating normally, that is, the input voltage of the direct current-direct current converter (DC-DC CONVERTER) is the reference voltage e1 or less, and the direct current-direct current converter ( DC
-DCCONVERTER) output voltage is reference voltage e3
In the following cases, the voltage comparator IC1 and the voltage comparator IC
2 means to output a low level signal.

The Low level signal output from the voltage comparator IC1 is the flip-flop FF of the control circuit CTL.
1 is input to the set terminal S. Also, voltage comparator IC
The low level signal output from the control circuit CT is
It is input to the set terminal S of the L flip-flop FF2.

The flip-flop FF1 to which the low level signal from the voltage comparator IC1 is input is input to the input Lo signal.
The w level signal is stored. Then, the output terminal Q of the flip-flop FF1 outputs a Low level signal. The low-level signal output from the output terminal Q of the flip-flop FF1 is input to the OR circuit OR4 and the OR circuit OR1.

The flip-flop FF2 to which the Low level signal from the voltage comparator IC2 is input stores the input Low level signal. The output terminal Q of the flip-flop FF2 outputs a low level signal, and the output terminal * Q outputs a high level signal. The low level signal output from the output terminal Q of the flip-flop FF2 is input to the logical sum circuit OR5, and the high level signal output from the output terminal * Q is input to the logical product circuit AND1.

The AND circuit AND1 inputs the signal from the PWM comparator 9 while inputting the high level signal from the output terminal * Q of the flip-flop FF2.
At this time, the AND circuit AND1 directly outputs the signal from the PWM comparator 9. AND circuit AN
The signal output from D1 is input to the OR circuit OR4.

As described above, the OR circuit OR4 receives the low level signal from the output terminal Q of the flip-flop FF1 and the signal from the AND circuit AND1 (the same signal as the signal from the PWM comparator 9). Enter. In this case, the OR circuit OR4 outputs the signal from the AND circuit AND1, that is, the signal from the PWM comparator 9 as it is.

The signal (P
The same signal as the signal output from the WM comparator 9) is input to the drive-1 (10). As a result, the drive-1 (10) can switch the main switching transistor Tr1 between the on state and the off state according to the signal from the PWM comparator 9.

Further, a logical sum circuit OR to which a Low level signal is inputted from the output terminal Q of the flip-flop FF1
1 also receives a signal from the synchronous rectification control circuit 13. In this case, the OR circuit OR1 outputs the signal from the synchronous rectification control circuit 13 as it is. The signal output from the OR circuit OR1 (the same signal as the signal output from the synchronous rectification control circuit 13) is input to the OR circuit OR5.

The OR circuit OR5, as described above, uses the signal from the OR circuit OR1 (the same signal as the signal output from the synchronous rectification control circuit 13) and the flip-flop F.
A low level signal from the output terminal Q of F2 is input. At this time, the OR circuit OR5 changes to the OR circuit OR1.
The same signal as the signal output from the synchronous rectification control circuit 13 is output. The signal output from the OR circuit OR5 (the synchronous rectification control circuit 13
Signal that is the same as the signal output from the drive-2
It is input in (11). As a result, drive-2 (1
In 1), according to a signal from the synchronous rectification control circuit 13, the synchronous rectification transistor Tr2 can be switched between an on state and an off state.

(2) DC-DC converter (DC-DC
When the input voltage of the CONVERTER becomes an overvoltage state, a DC-DC converter (DC-DC CONVERTER)
When the voltage input to (TER) is in the overvoltage state, the voltage comparator IC1 outputs a high level signal. In addition, a DC-DC converter (DC-DC CON
Since the output voltage of VERTER) is equal to or lower than the reference voltage e3, the voltage comparator IC2 outputs a low level signal.

High output from the voltage comparator IC1
The level signal is the flip-flop F of the control circuit CTL.
It is input to the set terminal S of F1. In addition, the voltage comparator I
The low-level signal output from C2 is the control circuit C
It is input to the set terminal S of the flip-flop FF2 of TL.

The flip-flop FF1 to which the High level signal from the voltage comparator IC1 is input is
The high level signal is stored. The output terminal Q of the flip-flop FF1 outputs a high level signal. The high-level signal output from the output terminal Q of the flip-flop FF1 is input to the OR circuit OR4 and the OR circuit OR1.

The flip-flop FF2 to which the Low level signal from the voltage comparator IC2 is input stores the input Low level signal. The output terminal Q of the flip-flop FF2 outputs a low level signal, and the output terminal * Q outputs a high level signal.
L output from the output terminal Q of the flip-flop FF2
The ow level signal is input to the OR circuit OR5, and the High level signal output from the output terminal * Q is input to the AND circuit AND1.

The AND circuit AND1 inputs the signal from the PWM comparator 9 while inputting the high level signal from the output terminal * Q of the flip-flop FF2. In this case, the AND circuit AND1 operates in the PWM comparator 9
The signal from will be output as it is. The signal output from the AND circuit AND1 (the same signal as the signal output from the PWM comparator 9) is input to the OR circuit OR4.

The OR circuit OR4, as described above, outputs the signal from the AND circuit AND1 (the same signal as the signal output from the PWM comparator 9) and the flip-flop FF1.
And a high level signal from the output terminal Q of. In this case, the logical sum circuit OR4 is the logical product circuit AND
A high level signal is output regardless of the signal from 1 (the same signal as the signal output from the PWM comparator 9). As a result, drive-1 (10)
The main switching transistor Tr1 is turned on regardless of the signal output from the WM comparator 9.

Further, the OR circuit OR1 inputs the high level signal from the output terminal Q of the flip-flop FF1 and inputs the signal from the synchronous rectification control circuit 13. In this case, the OR circuit OR1 outputs a high-level signal regardless of the signal from the synchronous rectification control circuit 13. Hi output from the OR circuit OR1
The gh level signal is input to the OR circuit OR5.

As described above, the OR circuit OR5 inputs the Low level signal from the output terminal Q of the flip-flop FF2 and the High level signal from the OR circuit OR1. At this time, the OR circuit OR5 changes to Hi.
It outputs a gh level signal. As a result, drive-2
(11) turns on the synchronous rectification transistor Tr2 regardless of the signal from the synchronous rectification control circuit 13.

As described above, the DC-DC converter (DC-
When the input voltage of DC CONVERTER) becomes the overvoltage state, the main switching transistor Tr1 and the synchronous rectification transistor Tr2 are forced to be in the ON state.

As a result, the DC-DC converter (DC-D
The voltage input to (C CONVERTER) is applied to the ground through the fuse F1, the signal line 14, the main switching transistor Tr1, the signal line 1, the signal line 2, the synchronous rectification transistor Tr2, and the signal line 26. At this time, an excessive current flows through the fuse F1, and the fuse F1 is blown.

Therefore, the fuse F1 is blown out, whereby the DC-DC converter (DC-DC CONVERTER).
TER) components, especially DC-DC converters (DC
It is possible to prevent an excessive voltage from being applied to the capacitor C3 provided in the input part of (-DC CONVERTER), and to prevent the capacitor C3 from burning.

Further, according to the DC-DC converter according to the present embodiment, the fuse for preventing the capacitor C3 from burning is unnecessary, and the number of constituent parts is reduced.

Further, since the fuse for preventing the capacitor C3 from being burnt out is unnecessary, the resistance in the DC-DC converter (DC-DC CONVERTER) is reduced, and the DC-DC converter (DC-DC CONVERT) is reduced.
(ER) conversion efficiency is improved.

(3) When the signal line 4 is in the disconnection state When the signal line 4 is in the disconnection state, the DC-DC converter (DC-DC C) is used as described in the first embodiment.
The output voltage of (ONVERTER) may fall into an overvoltage state.

DC-DC converter (DC-DC CON
When the output voltage of (VERTER) falls into the overvoltage state, the output voltage becomes higher than the reference voltage e3, so that the voltage comparator IC2 outputs a high level signal.

On the other hand, a DC-DC converter (DC-DC
Since the input voltage of CONVERTER) is equal to or lower than the reference voltage e1, the voltage comparator IC1 outputs a low level signal.

The Low level signal output from the voltage comparator IC1 is the flip-flop FF of the control circuit CTL.
1 is input to the set terminal S. Also, voltage comparator IC
The High level signal output from the control circuit C
It is input to the set terminal S of the flip-flop FF2 of TL.

The flip-flop FF1 to which the Low level signal from the voltage comparator IC1 is input is input to the input Lo signal.
The w level signal is stored. Then, the output terminal Q of the flip-flop FF1 outputs a Low level signal. The low-level signal output from the output terminal Q of the flip-flop FF1 is input to the OR circuit OR4 and the OR circuit OR1.

Further, the flip-flop FF2 to which the High level signal from the voltage comparator IC2 is input stores the input High level signal. The output terminal Q of the flip-flop FF2 outputs a high level signal, and the output terminal * Q outputs a low level signal. The high level signal output from the output terminal Q of the flip-flop FF2 is input to the OR circuit OR5, and the low level signal output from the output terminal * Q is input to the AND circuit AND1.

The AND circuit AND1 inputs the signal from the PWM comparator 9 while inputting the Low level signal from the output terminal * Q of the flip-flop FF2. In this case, the AND circuit AND1 operates in the PWM comparator 9
A low-level signal is output regardless of the signal from. L output from the AND circuit AND1
The ow level signal is input to the OR circuit OR4.

As described above, the OR circuit OR4 inputs the low level signal from the AND circuit AND1 and the low level signal from the output terminal Q of the flip-flop FF1. In this case, the OR circuit OR4 is Lo
A w level signal will be output. As a result, the drive-1 (10) is irrespective of the signal output from the PWM comparator 9, and the main switching transistor Tr1
To turn off.

Further, the OR circuit OR1 inputs the signal of the Low level from the output terminal Q of the flip-flop FF1 and inputs the signal from the synchronous rectification control circuit 13. In this case, the OR circuit OR1 outputs the signal from the synchronous rectification control circuit 13 as it is. The signal output from the OR circuit OR1 (the same signal as the signal output from the synchronous rectification control circuit 13) is input to the OR circuit OR5.

As described above, the OR circuit OR5 is the same as the high level signal from the output terminal Q of the flip-flop FF2 and the signal from the OR circuit OR1 (the same signal as the signal output from the synchronous rectification control circuit 13). Signal) and input. At this time, the OR circuit OR5 is the OR circuit OR.
The high level signal is output regardless of the signal from 1 (the same signal as the signal output from the synchronous rectification control circuit 13). As a result, the drive-2 (11) turns on the synchronous rectification transistor Tr2 regardless of the signal from the synchronous rectification control circuit 13.

As described above, the DC-DC converter (DC-
When the output voltage of DC CONVERTER) becomes an overvoltage state, the main switching transistor Tr1 is forcibly turned off, and at the same time, the synchronous rectification transistor Tr2 is forcibly turned on.

As a result, the signal line 26, the transistor Tr2 for synchronous rectification, the signal line 2, the signal line 1, the choke coil L
1, the signal line 15, the resistor R1, and the signal line 16 are connected, and a DC-DC converter (DC-DC C
The output voltage of ONVERTER) is clamped to the voltage (0V) of the ground connected to the signal line 26.

Therefore, a DC-DC converter (DC-DC)
It is possible to prevent the overvoltage from being applied to the load of the CONVERTER, and at the same time, to prevent the overvoltage from being applied to the constituent elements of the DC-DC converter (DC-DC CONVERTER), particularly the smoothing capacitor C1. Can be prevented.

Further, according to the direct current-direct current converter (DC-DC CONVERTER) of the present embodiment,
It is not necessary to use a high withstand voltage organic capacitor as the smoothing capacitor C1, and a fuse for preventing burnout is unnecessary, and the number of constituent parts is reduced.

Further, since the fuse for preventing the capacitor C1 from being burnt out is unnecessary, the resistance in the DC-DC converter is reduced, and the DC-DC converter (DC-DC CONVERT) is reduced.
(ER) conversion efficiency is improved.

(4) Main switching transistor T
When r1 has a short circuit failure When the main switching transistor Tr1 has a short circuit failure, the signal line 14
Since the signal line 1 is connected to the signal line 1, the output voltage of the DC-DC converter (DC-DCCONVERTER) may fall into an overvoltage state.

When the output voltage falls into the overvoltage state due to the short-circuit failure of the main switching transistor Tr1, the output voltage becomes larger than the reference voltage e3, so that the voltage comparator I
C2 will output a high level signal.

On the other hand, a DC-DC converter (DC-DC
Since the input voltage of CONVERTER) is equal to or lower than the reference voltage e1, the signal OV1 output from the voltage comparator IC1
Becomes a low level signal.

At this time, the control circuit CTL controls the main switching transistor Tr1 to be forcibly turned off and the synchronous rectification transistor Tr2 forcibly turned on at the same time as described in (2) above. To do. However, since the main switching transistor Tr1 has a short circuit failure, a DC-DC converter (DC-D
The voltage applied to the CCONVERTER) is applied to the fuse F1, the signal line 14, the main switching transistor T
It is short-circuited via r1, the signal line 1, the signal line 2, and the synchronous rectification transistor Tr2. At this time, fuse F
1 is melted by a short circuit current.

As a result, the DC-DC converter (DC-D
The voltage applied to C COVERTER is cut off in an extremely short time, and it is possible to prevent the overvoltage from being applied to the load of the DC-DC converter. It is possible to prevent an overvoltage from being applied to the constituent elements of the DC-DC converter.

Further, according to the direct current-direct current converter (DC-DC CONVERTER) of the present embodiment,
It is not necessary to use a high withstand voltage organic capacitor as the smoothing capacitor C1, and a fuse for preventing burnout is unnecessary, and the number of constituent parts is reduced.

Further, since the fuse for preventing the burning of the smoothing capacitor C1 is not required, the resistance in the DC-DC converter (DC-DC CONVERTER) is reduced, and the DC-DC converter (DC-DC) is reduced. DC CONV
ERTER) conversion efficiency is improved.

[0423]

The DC-DC converter according to the present invention (D
According to C-DC CONVERTER, when the input / output voltage of the DC-DC converter is in the overvoltage state, the first switching element and the second switching element (main switching transistor and synchronous rectification transistor) are overvoltage-controlled. By using as a protection circuit, without complicating the circuit configuration, the components of the DC-DC converter, and,
It is possible to prevent an overvoltage from being applied to the load of the DC-DC converter.

As a result, it is possible to prevent smoking and ignition of the organic condenser used in the DC-DC converter, and to prevent the DC-DC CONVERT device (DC-DC CONVERT).
(ER) can be downsized and conversion efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a DC-DC converter (DC-D) according to the present invention.
A diagram showing the configuration of the first embodiment of C CONVERTER).

FIG. 2 is a diagram showing an internal configuration of a control circuit CTL according to the first embodiment.

FIG. 3 is a view showing another embodiment of the DC-DC converter according to the first embodiment (DC-DC CONVERTER).

4 is a DC-DC converter of FIG. 3 (DC-DC CO
NVERTER) corresponding to the internal configuration of the control circuit CTL

FIG. 5 is a DC-DC converter (DC-D) according to the present invention.
The figure which shows the structure of the 2nd implementation form of C CONVERTER).

FIG. 6 is a diagram showing an internal configuration of a control circuit CTL according to a second embodiment.

FIG. 7 is a view showing another embodiment of the DC-DC converter according to the second embodiment (DC-DC CONVERTER).

8 is a DC-DC converter of FIG. 7 (DC-DC CO
NVERTER) corresponding to the internal configuration of the control circuit CTL

FIG. 9 is a DC-DC converter (DC-D) according to the present invention.
A diagram showing the configuration of the third embodiment of C CONVERTER).

FIG. 10 is a DC-DC converter according to the present invention (DC-
A diagram showing a configuration of a fourth embodiment of DC CONVERTER).

FIG. 11 is a diagram showing an internal configuration of a control circuit CTL according to a fourth embodiment.

FIG. 12 is a conventional DC-DC converter (DC-DC C
ONVERTER) configuration diagram

[Explanation of symbols]

1 ... Signal line 2 ... Signal line 14 ... Signal line FF: flip-flop Tr1 ... Main switching transistor Tr2 · · Transistor for synchronous rectification IC1 ... Voltage comparator IC2 ... Voltage comparator CTL ... Control circuit L1 ... Choke coil F1 ... Fuse e1 ... power supply e2 ... power supply C1 ... Capacitor C2: Capacitor

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-199740 (JP, A) JP-A-4-54864 (JP, A) JP-A-63-59763 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H02M 3/155

Claims (43)

(57) [Claims] 1. A storage unit for storing electric power from a power source, a first switch element for switching connection and disconnection of the power source and the storage unit, and the storage unit provided between the storage unit and ground. The second switch element for switching between connecting and disconnecting the means and the ground, and the first switch element and the second switch element are alternately connected to each other, and the output voltage from the accumulating means has a constant value. A DC-DC converter of a synchronous rectification system having a control unit for keeping the output voltage, monitoring the output voltage from the storage unit, and outputting a signal when the output voltage exceeds a predetermined voltage value. And an overvoltage detection means for controlling the first switch element to be in a disconnection state and a connection to the second switch element when a signal from the overvoltage detection means is input. And controls so that the state, DC synchronous rectification comprising a clamping means, the clamping the output voltage from said storage means to the ground level - DC converter. 2. The overvoltage detecting means compares a reference voltage generating means for generating a reference voltage with the output voltage from the accumulating means, and the output voltage becomes larger than the reference voltage. The DC-DC converter according to claim 1, further comprising a voltage comparison unit that outputs the signal. 3. The circuit according to claim 1, further comprising short-circuiting means for short-circuiting the voltage from the power supply when the first switch element fails in a short-circuited state to bring the second switch element into a connected state. Synchronous rectification DC-DC converter. 4. The DC-DC converter of the synchronous rectification system according to claim 3, further comprising a cutoff unit that cuts off an input from the power source by the electric power short-circuited by the short-circuiting unit. 5. The cutoff means is a fuse blown by the electric power short-circuited by the short-circuit means.
Synchronous rectification type DC-DC converter. 6. The synchronous rectification type DC-DC converter according to claim 1, further comprising a cutoff unit which is provided between the power supply and the first switch element and which cuts off an input from the power supply. 7. When the first switch element fails, the clamp means short-circuits the electric power from the power source by putting the second switch element into a connected state, and the cutoff means comprises: 7. The input from the power supply is cut off by using the electric power short-circuited by the clamp means.
The DC-DC converter of the synchronous rectification method according to item 1. 8. A storage unit for storing electric power from a power source, a first switch for switching connection and disconnection of the power source and the storage unit, and a storage unit arranged between the storage unit and the ground. A second switch for switching between connecting and disconnecting the ground and the ground, and the first switch element and the second switch element are alternately connected so that the output voltage from the storage means maintains a constant value. Control means, detecting means for detecting that the output voltage of the accumulating means exceeds a predetermined voltage value, and controlling the first switch to be in a disconnection state in response to the detection of the detecting means. And a clamp means for controlling the second switch to be in a connected state, and a synchronous rectification type DC-DC converter. 9. The detecting means compares a reference voltage generating means for generating a reference voltage with the output voltage of the accumulating means, and the output voltage of the accumulating means is larger than the reference voltage. 9. The DC-DC converter of the synchronous rectification system according to claim 8, further comprising a voltage comparison unit that outputs a signal at times. 10. The short-circuit means for short-circuiting the power from the power supply by forcing the second switch into the connection state when the first switch fails in the short-circuit state. Synchronous rectification type DC-DC converter. 11. The DC-DC converter of the synchronous rectification system according to claim 10, further comprising a cutoff unit that cuts off an input from the power source. 12. The DC-DC converter of the synchronous rectification system according to claim 11, wherein the breaking means is a fuse. 13. The DC-DC converter of the synchronous rectification system according to claim 8, further comprising a shutoff means provided between the power source and the first switch element for shutting off an input from the power source. 14. When the first switch element fails, the clamp means short-circuits the electric power from the power source by putting the second switch element into a connected state, and the cutoff means comprises: The input from the power source is shut off by using the electric power short-circuited by the clamp means.
3. The synchronous rectification type DC-DC converter according to item 3. 15. Storage means for storing electric power from a power supply, a first switch element for switching connection and disconnection of the power supply and the storage means, and the storage means provided between the storage means and the ground. The second switch element for switching between connecting and disconnecting the means and the ground, and the first switch element and the second switch element are alternately connected to each other, and the output voltage from the accumulating means has a constant value. A control circuit for a DC-DC converter of a synchronous rectification system, comprising: a first control means for keeping the output voltage from the storage means, and the output voltage has a predetermined voltage value. Overvoltage detection means for detecting that the output voltage exceeds the predetermined voltage value, and a control for disconnecting the first switch element when the overvoltage detection means detects that the output voltage exceeds a predetermined voltage value. The controlled to the connected state to the second switching element, a control circuit and a second control means for the output voltage from said storage means to the ground level while. 16. The overvoltage detection means compares a reference voltage generation means for generating a reference voltage with the output voltage from the storage means, and the output voltage becomes larger than the reference voltage. 16. A voltage comparison means for outputting a signal at times.
The described control circuit. 17. A storage unit for storing electric power from a power supply, a first switch element for switching connection and disconnection of the power supply and the storage unit, and a storage unit provided between the storage unit and the ground. The second switch element for switching between connecting and disconnecting the means and the ground, and the first switch element and the second switch element are alternately connected to each other, and the output voltage from the accumulating means has a constant value. A control circuit for a DC-DC converter of a synchronous rectification system, comprising: a first control means for keeping the output voltage from the storage means, and the output voltage has a predetermined voltage value. Detecting means for detecting the exceeding, and controlling the first switch element to be in a disconnection state according to the detection of the detecting means and the second means.
Second control means for controlling the switching element to be brought into a connected state. 18. The detecting means compares the reference voltage with a reference voltage generating means for generating a reference voltage, and the output voltage of the accumulating means is larger than the reference voltage. The control circuit according to claim 17, further comprising a voltage comparison unit that outputs a signal at times. 19. A synchronous rectification type DC-DC converter, a main switch, a synchronous rectification switch that is alternately connected to the main switch, and an output voltage of the DC-DC converter is an overvoltage. A first control signal for turning off the main switch and a second control signal for turning on the synchronous rectification switch when the overvoltage detecting means detects an overvoltage. A synchronous rectification type DC-DC converter comprising: a control unit that outputs a control signal. 20. In a synchronous rectification type DC-DC converter, a main switch, a switch for synchronous rectification that is alternately connected to the main switch, and an output voltage of the DC-DC converter is an overvoltage. And a control for forcibly turning off the main switch and forcibly turning on the synchronous rectification switch when the overvoltage detection means detects an overvoltage. A DC-DC converter of the synchronous rectification system, which comprises: 21. The synchronous rectification type direct current-DC converter according to claim 19, further comprising: an inductor connected to the main switch; and a capacitor connected to the inductor for smoothing an output voltage from the inductor. DC converter. 22. The synchronous rectification type DC-DC converter according to claim 19, wherein said overvoltage detecting means outputs a detection signal when detecting that the output voltage of said DC-DC converter is an overvoltage. . 23. When the detection signal is output from the overvoltage detection means, the control means stores the detection signal, and a first control signal for turning off the main switch and a synchronous rectification switch. Second to turn on
23. A memory circuit for outputting the control signal of
Synchronous rectification type DC-DC converter. 24. The synchronous rectification system according to claim 19, further comprising feedback means for feedback controlling the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter constant. DC-DC converter. 25. The control means outputs a second control signal to turn on the synchronous rectification switch when the main switch fails in a short circuit state.
24. The synchronous rectification type DC-DC converter according to claim 23, wherein an input from a power source is short-circuited. 26. The DC-DC converter of the synchronous rectification system according to claim 19, further comprising a cutoff unit that is provided between the main switch and the power supply and cuts off an input from the power supply. 27. A control circuit for controlling a synchronous rectification type DC-DC converter comprising a main switch and a synchronous rectification switch which is alternately connected to the main switch, wherein the DC- Overvoltage detection means for detecting that the output voltage of the DC converter is an overvoltage; a first control signal for turning off the main switch when the overvoltage detection means detects an overvoltage; and the synchronous rectification A control circuit that outputs a second control signal for turning on the switch. 28. A main switch, a switch for synchronous rectification that is alternately connected to the main switch, an inductor connected to the main switch, and an output voltage from the inductor connected to the inductor and smoothed. A control circuit for controlling a synchronous rectification type DC-DC converter comprising a capacitor, an overvoltage detecting unit for detecting that the output voltage of the DC-DC converter is an overvoltage, and the overvoltage detecting unit. Control circuit that outputs a first control signal for turning off the main switch and a second control signal for turning on the synchronous rectification switch when an overvoltage is detected by the control circuit. . 29. A control circuit for controlling a DC-DC converter of a synchronous rectification system, comprising: a main switch; and a synchronous rectification switch that is alternately connected to the main switch. An overvoltage detecting means for detecting that the output voltage of the DC converter is an overvoltage; and a control for forcibly turning off the main switch when the overvoltage detecting means detects an overvoltage and the synchronous rectification switch. And a control means for controlling to forcibly turn on. 30. A main switch, a switch for synchronous rectification that is alternately connected to the main switch, an inductor connected to the main switch, and an output voltage from the inductor connected to the inductor and smoothed. A control circuit for controlling a synchronous rectification type DC-DC converter comprising a capacitor, an overvoltage detector for detecting that the output voltage of the DC-DC converter is an overvoltage, and the overvoltage detector. Control circuit for controlling the main switch to be forcibly turned off and the synchronous rectification switch to be forcibly turned on when the overvoltage is detected by the control circuit. 31. The overvoltage detection means outputs a detection signal when it detects that the output voltage of the DC-DC converter is an overvoltage, according to any one of claims 27 to 29. Control circuit. 32. When the detection signal is output from the overvoltage detection means, the control means stores the detection signal and also outputs a first control signal for turning off the main switch and the synchronous rectification. 32. The control circuit according to claim 31, further comprising a memory circuit which outputs a second control signal for turning on the switch. 33. The control means short-circuits the input from the power source by outputting a second control signal for turning on the synchronous rectification switch when the main switch fails. The control circuit according to any one of claims 27 to 29. 34. A feedback means for feedback controlling the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter at a constant value. The control circuit described in. 35. A control circuit for controlling a synchronous rectification type DC-DC converter comprising a main switch and a synchronous rectification switch which is alternately connected to the main switch, wherein a DC-DC Receiving means for receiving a conversion request stop request signal, and for turning on the synchronous rectification switch and a first control signal for turning off the main switch when the receiving means receives the stop request signal And a control means for outputting the second control signal. 36. A main switch, a switch for synchronous rectification that is alternately connected to the main switch, an inductor connected to the main switch, and an inductor connected to the inductor to smooth the output voltage from the inductor. DC of the synchronous rectification system with a capacitor
In a control circuit for controlling a DC converter, receiving means for receiving a stop request signal for DC-DC conversion processing; and a first means for turning off the main switch when the receiving means receives the stop request signal. Control signal for outputting a control signal for controlling the synchronous rectification switch and a second control signal for turning on the synchronous rectification switch. 37. A control circuit for controlling a DC-DC converter of a synchronous rectification type, comprising: a main switch; and a synchronous rectification switch that is alternately connected to the main switch. Receiving means for receiving a stop request signal for DC conversion processing, and when the receiving means receives the stop request signal, while controlling to forcibly turn off the main switch,
A control unit for controlling the synchronous rectification switch to be forcibly turned on. 38. A main switch, a synchronous rectification switch that is alternately connected to the main switch, an inductor connected to the main switch, and an inductor connected to the inductor to smooth an output voltage from the inductor. In the control circuit for controlling the DC-DC converter of the synchronous rectification method comprising a capacitor, receiving means for receiving a stop request signal of the DC-DC conversion process, when the receiving means receives the stop request signal, While instructing to forcibly turn off the main switch,
A control unit for controlling the synchronous rectification switch to be forcibly turned on. 39. The control circuit according to claim 35, wherein the stop request signal is a signal indicating that the output voltage of the DC-DC converter is an overvoltage. 40. The feedback means for feedback controlling the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter at a constant value. Control circuit. 41. The control means short-circuits the input from the power supply by outputting a second control signal for turning on the switch for synchronous rectification when the main switch fails. The control circuit according to claim 35 or 36. 42. A control circuit for controlling a synchronous rectification type DC-DC converter comprising a main switch and a synchronous rectification switch that is alternately connected to the main switch, wherein a DC-DC Receiving means for receiving a conversion request stop request signal, when the receiving means receives the stop request signal, by controlling to turn off the main switch and to turn on the synchronous rectification switch, Control means for stopping the output of the DC-DC converter. 43. A control circuit for controlling a DC-DC converter of a synchronous rectification system, comprising: a main switch; and a switch for synchronous rectification that is alternately connected to the main switch. A voltage input terminal for inputting the output voltage of the DC converter, and an overvoltage detection means for outputting a detection signal when detecting that the voltage input to the voltage input terminal exceeds a predetermined voltage, and the overvoltage detection When the means outputs the detection signal, by controlling the main switch to be turned off and the synchronous rectification switch to be turned on,
Clamping means for clamping the output of the DC-DC converter to the ground level.