JP3349897B2 - 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 technology for protecting a step-down DC-DC converter from overvoltage, and more particularly, to protecting a DC-DC converter from overvoltage on the output side or overvoltage on the output side. Related to the technology to prevent. Alternatively, the present invention relates to a technique for protecting a circuit and a load of a DC-DC converter (DC-DC converter) 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 supply 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, general batteries have a characteristic that the voltage decreases as the discharge proceeds. For this reason, the portable electronic device includes a DC-DC converter that stabilizes the output voltage of the battery.

[0004] One of the performances of a portable electronic device is a time period during which the battery operates effectively (effective operation time).
is important. In order to keep this effective working time long,
It is necessary not only to reduce the power consumption of the portable electronic device but also to improve the conversion efficiency of a DC-DC converter. Because DC-
This is because the conversion efficiency of the DC-DC converter is directly reflected on the power consumption rate of the battery.

[0005] DC-DC converter
As a method of improving the conversion efficiency of a DC-DC converter, a method of using a DC-DC converter of a synchronous rectification system is generally used. According to the DC-DC converter of the synchronous rectification system, the conversion efficiency can be improved by about 10% as compared with a conventional DC-DC converter.

A DC-DC converter (DC-DC converter)
TER) conversion efficiency is DC-DC converter (DC-DC CONVE
RTER) capacitor performance. For example, recent DC-DC converters (DC-DC converters) emit a high frequency in order to improve conversion efficiency and reduce the size of the device. Such a DC-DC converter requires a smoothing capacitor in an output part in order to reduce a phase error.

The smoothing capacitor has an equivalent series resistance (E
SR), and when the resistance value of the equivalent series resistance (ESR) is large, the DC-DC converter (DC-DC CONVERTE
R) The conversion efficiency deteriorates.

Therefore, a DC-DC converter (DC-DC CONV
In order to improve the conversion efficiency of the ERTER, a capacitor having a small equivalent series resistance (ESR) is required.
An organic capacitor is known as a capacitor having a small equivalent series resistance (ESR).

When an organic capacitor is used as a smoothing capacitor, a DC-DC converter (DC-DC converter) is used.
Since the conversion efficiency of R) is improved, heat generation is reduced even when a large current flows. For this reason, a DC-DC converter using an organic capacitor (DC-DC converter) is 3 amps or less.
It is designed to be used in devices capable of handling large currents of about 5 amps.

When a DC-DC converter using an organic capacitor as a smoothing capacitor is used in a device corresponding to a large current, a DC-DC converter (DC-DC converter) is used.
-DC CONVERTER) will receive a large current.
It is preferable to use an organic capacitor having a large allowable ripple also for a capacitor used for an input section of a DC-DC converter.

As described above, the organic capacitor has the advantage of being excellent in high frequency characteristics and temperature characteristics, but has the disadvantage that it is easily broken by an overvoltage and causes smoke and ignition.

For this reason, a DC-DC converter (DC-DC CO
When using an organic capacitor for NVERTER), a mechanism is needed to protect the organic capacitor from overvoltage. DC-
The causes of overvoltage in the DC-DC converter include the case where an overvoltage occurs in the output section due to a circuit failure in the DC-DC converter,
DC-DC converter (DC-DC converter) due to failure of battery or charger, or use of inappropriate battery or charger.
It is considered that an overvoltage is input to R).

First, a DC-DC converter (DC-DC converter)
If an overvoltage occurs at the output of the DC-DC converter, it is necessary to protect the smoothing capacitor provided at the output of the DC-DC converter.

As a method of protecting the smoothing capacitor, there is a method of providing a ZENER diode at the output of a DC-DC converter. In this method, when the voltage output from the DC-DC converter exceeds the standard voltage of the Zener diode, the Zener diode is burned, and the DC-DC converter and the load are connected. Is short-circuited.

In this case, a DC-DC converter (DC-DC CO
NVERTER) and the load are short-circuited to stop the flow of current, so that an overvoltage can be prevented from being applied to the organic capacitor.

A DC-DC converter (DC-DC converter)
TER) inputs an overvoltage, it is necessary to protect the capacitor provided at the input of the DC-DC converter (DC-DC converter).

However, conventionally, protection of a capacitor provided at an input portion of a DC-DC converter has not been regarded as important. Because the DC-DC converter has a mechanism for cutting the path of the input voltage, the DC-DC converter is provided at the output of the DC-DC converter. This is because it does not directly affect the circuit.

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

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

The synchronous rectification transistor Tr2 is, like the diode D1, a main switching transistor T2.
This is a freewheel switch circuit that releases energy stored in the choke coil L1 to the output side while r1 is in the off state. This synchronous control transistor Tr2
Is a field effect transistor (FET) that is 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 sense resistor R1 for measuring a current value flowing from a DC-DC converter to a load.
It is.

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

When the voltage from which the AC component has been removed by the capacitor C1 exceeds the specified voltage, the Zener diode D2 is turned on, and the DC-DC converter (DC-D
Clamp the output voltage from C CONVERTER to the specified voltage. Further, when the overvoltage increases, the ZENER diode D2 burns out and a DC-DC converter (DC-DCCON
VERTER) 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. Further, an external ON command value or OFF command value and a target voltage Vref are input to the control circuit CTL.

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

The control circuit CTL compares the output voltage FB from the resistor R1 with a target voltage Vref from the outside and determines that the output voltage of the DC-DC converter is a predetermined voltage value. The main switching transistor Tr1 and the synchronous rectification transistor Tr2
Switch on and off.

The above DC-DC converter (DC-DC CONVER
When the TER) is operating normally, the output voltage of the DC-DC converter is sufficiently lower than the standard voltage of the Zener diode D2, so that 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 converter)
TER) is overvoltage, the output voltage of the DC-DC converter (DC-DC converter) will be ZENE
It becomes higher than the standard voltage value of the R diode D2. When the output voltage exceeds the standard voltage, the ZENER diode D
2 is turned on. In this case, the output voltage of the DC-DC converter is clamped to the standard voltage of the Zener diode D2. Thereby, it is possible to prevent an overvoltage from being applied to the load.

Further, the DC-DC converter (DC-D
C CONVERTER) does not have a mechanism to limit the current flowing through the Zener diode D2.
The ENER diode D2 burns out. In this case, the DC
A short circuit occurs between the DC converter and the load. As a result, no current flows through the smoothing capacitor C1, and burning of the smoothing capacitor C1 can be prevented.

A DC-DC converter (DC-DC converter)
There is also a method of using a thyristor (SCR) as a method of generating a load short circuit when an overvoltage condition occurs in the TER). There was a problem of inviting.

On the other hand, a DC-DC converter (DC-DC converter)
TER), when an overvoltage is input to the control circuit CTL,
Turn off the main switching transistor. In this case, no current flows in the DC-DC converter, so that the DC-DC converter
-DC CONVERTER) does not affect the output circuit. For this reason, DC-DC converter (DC-DC CONV
ERTER) has no protection mechanism against input overvoltage.

[0033]

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. Does not function. ZEN
If the ER diode fails in open mode,
There is a problem that an organic capacitor provided in an output part of a DC-DC converter is burned and causes smoke or ignition.

Further, since it is impossible to specify whether the ZENER diode fails in the open mode or the short mode, the ZENER diode is used as a protection circuit for the DC-DC converter.
Utilizing an ER diode is inappropriate.

On the other hand, in order to prevent burning of the organic capacitor due to overvoltage, a method of using an organic capacitor having a high withstand voltage is conceivable. Requires multiple organic capacitors. For this reason, there is a problem that the circuit becomes large. Furthermore, since the high withstand voltage organic capacitor has a large equivalent series resistance (ESR) resistance value,
There is also a problem that the conversion efficiency of the DC-DC converter is deteriorated.

On the other hand, in order to prevent burning of the organic capacitor due to overvoltage, a DC-DC converter (DC-DC converter) is used.
There is a method of providing a fuse for preventing burnout in each of the organic capacitors used for the converter. However, in this method, a DC-DC converter is used.
However, there is a problem that the number of components increases and the production cost of the DC-DC converter increases. Further, when a fuse is provided for each organic capacitor, there is a problem that the conversion efficiency of a DC-DC converter is reduced due to the resistance of the fuse.

A DC-DC converter (DC-DC converter)
Since organic capacitors are being used at the input of TER), it is also necessary to protect these organic capacitors.

Accordingly, the present invention has been made in view of the above problems, and has been made in a synchronous rectification type step-down DC-DC converter without complicating the circuit configuration. An object of the present invention is to provide a technique for protecting a DC-DC converter from a voltage overvoltage, thereby preventing smoke and ignition due to the overvoltage. In addition, DC-DC converter (DC
-DC CONVERTER) and improve the conversion efficiency. It is another object of the present invention to prevent an overvoltage from being applied to a load of a DC-DC converter without complicating a circuit configuration.
Further, the present invention has been made in view of the above-mentioned problems, and a step-down DC-DC converter (DC-DC) of a synchronous rectification system.
CONVERTER), to provide a technique for preventing an overvoltage of an output voltage without complicating a circuit, and to contribute to miniaturization and improvement of reliability of a device.

[0039]

The present invention employs the following means in order to solve the above-mentioned problems. First, first
The invention is characterized in that a storage means for storing power from a power supply, a first switch element for switching between connection and disconnection of the power supply and the storage means, and a storage means provided between the storage means and ground, A second switch element for switching connection and disconnection between the first switch element and the ground, and controlling connection and disconnection of the first switch element and the second switch element to maintain a constant output voltage from the storage means. A DC-DC converter of a synchronous rectification type, comprising: a control unit configured to monitor an output voltage from the storage unit and output a signal when the output voltage exceeds a predetermined voltage value. Overvoltage detection means, and when a signal from the overvoltage detection means is input, the first switch element is turned off and the second switch element is turned on to output the signal from the storage means. DC synchronous rectification type that includes a clamping means for clamping the voltage to a ground level - a DC converter. The above-mentioned overvoltage detection means compares the reference voltage with an output voltage from the storage means, and outputs the signal when the output voltage becomes larger than the reference voltage. And a voltage comparing means for outputting the same. In the DC-DC converter according to the first invention, when the first switch element fails in a short-circuit state, the second switch element is connected to short-circuit the voltage from the power supply. A short-circuiting means may be further provided, and in addition to the above-described short-circuiting means, an interrupting means for interrupting an input from a power supply by electric power short-circuited by the short-circuiting means may be further provided. As the interrupting means, a fuse blown by the power short-circuited by the short-circuiting means can be exemplified. In addition, the DC-DC converter according to the first invention may further include a cutoff unit provided between the power supply and the first switch element, for cutting off an input from the power supply. At this time, when the first switch element fails, the clamp means short-circuits the power from the power supply by connecting the second switch element, and the cut-off means cuts off the input from the power supply by the short-circuited power. You may make it cut off.

Next, a second invention provides a storage means for storing power from a power supply, a first switch for switching connection and disconnection of the power supply and the storage means, and a switch between the storage means and ground. A second switch for switching between connection and disconnection of the storage means and the ground, and controlling connection and disconnection of the first and second switches so that the output voltage from the storage means has a constant value. Control means for keeping the output voltage of the storage means, detection means for detecting that the output voltage of the storage means has exceeded a predetermined voltage value, and disconnection of the first switch according to the detection of the detection means And a clamp means for connecting the second switch to a connected state. The above-mentioned detecting means compares, for example, a reference voltage generating means for generating a reference voltage with the reference voltage and the output voltage of the accumulating means, and outputs a signal when the output voltage of the accumulating means becomes larger than the reference voltage. Voltage comparing means may be provided. Further, the DC-DC converter according to the second aspect of the present invention, when the first switch fails in a short-circuit state,
May be further provided with a short-circuit means for short-circuiting the power from the power supply by forcibly setting the switch to a connected state. You may do so. A fuse can be exemplified as the blocking means. Further, the DC-DC converter according to the second aspect of the present invention may further include a cutoff unit provided between the power supply and the first switch element, for cutting off an input from the power supply. At this time, when the first switch fails, the clamp means short-circuits the power from the power supply by setting the second switch to the connected state, and uses the short-circuited power to cause the cut-off means to operate the input from the power supply. May be blocked.

Next, a third invention provides a storage means for storing power from a power supply, a first switch element for switching connection and disconnection of the power supply and the storage means, and a storage means provided between the storage means and the ground. A second switch element for switching connection and disconnection of the storage means and the ground, and controlling connection and disconnection of the first switch element and the second switch element so that the output voltage from the storage means becomes a constant value. A control circuit for a synchronous rectification type DC-DC converter, comprising: a first control means for maintaining the output voltage from the storage means; and Overvoltage detection means for detecting that the output voltage exceeds the predetermined voltage value, and when the output voltage from the storage means exceeds a predetermined voltage value, the first switch element is turned off. With And said second switching element in the connected state, a control circuit and a second control means for a ground level output voltage from said storage means. The above-mentioned overvoltage detecting means compares a reference voltage generating means for generating a reference voltage with the reference voltage and an output voltage from an accumulating means, and when an output voltage from the accumulating means becomes larger than the reference voltage. And a voltage comparing means for outputting a signal.

Next, a fourth invention provides a storage means for storing power from a power supply, a first switch element for switching between connection and disconnection of the power supply and the storage means, and a connection between the storage means and ground. A second switch element that is provided between the storage means and switches connection and disconnection of the ground from the storage means, and controls connection and disconnection of the first switch element and the second switch element to control the connection and disconnection from the storage means. A control circuit for a DC-DC converter of a synchronous rectification system, comprising: a first control means for keeping an output voltage of a constant value, and monitoring an output voltage from the storage means. Detecting means for detecting that the output voltage has exceeded a predetermined voltage value;
A second control unit for setting the output voltage from the storage unit to the ground level by setting the first switch element to a disconnected state and setting the second switch element to a connected state in response to detection by the detection unit; It is a control circuit provided with. The detection means compares a reference voltage with an output voltage from a storage means, and outputs a signal when the output voltage of the storage means becomes larger than the reference voltage. And a voltage comparing means for outputting.

According to a fifth aspect of the present invention, in a DC-DC converter of a synchronous rectification system, a main switch, a switch for synchronous rectification, and detecting that an output voltage of the DC-DC converter is an overvoltage. Overvoltage detection means, and control for outputting a first control signal for turning off the main switch and a second control signal for turning on the synchronous live flow switch when the overvoltage detection means detects an overvoltage. And a DC-DC converter of a synchronous rectification system comprising: Further, the DC-DC converter according to the fifth invention may further include an inductor connected to the main switch, and a capacitor connected to the inductor and smoothing an output voltage from the inductor. Further, the DC-DC converter according to the fifth invention may further include feedback means for performing feedback control of the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter constant. . Further, the DC-DC converter according to the fifth aspect of the present invention may further include a cutoff unit provided between the main switch and the power supply, for cutting off an input from the power supply.

According to a sixth aspect of the present invention, in a synchronous rectification type DC-DC converter, a main switch, a synchronous rectification switch, and detecting that an output voltage of the DC-DC converter is an overvoltage. An overvoltage detecting means, and a control means for forcibly turning off the main switch and forcibly turning on the synchronous live current switch when the overvoltage detecting means detects an overvoltage. It is a DC converter. The DC-DC converter according to the sixth invention may further include an inductor connected to the main switch, and a capacitor connected to the inductor and smoothing an output voltage from the inductor. In the DC-DC converter according to the sixth invention, the overvoltage detection means may output a detection signal when detecting that the output voltage of the DC-DC converter is an overvoltage, for example. . In response to this, when the detection signal is output from the overvoltage detection means, the control means stores the detection signal, and sets a first control signal for turning off the main switch and a synchronous rectification switch. A memory circuit for outputting a second control signal for turning on the memory may be provided. Then, when the main switch fails in the short-circuit state, the control unit may output the second control signal to turn on the synchronous rectification switch, thereby causing the input from the power supply to be short-circuited. . The DC-DC converter according to the sixth invention may further include feedback means for performing feedback control of the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter constant. . In addition, the DC-
The DC converter may further include a cutoff unit provided between the main switch and the power supply, for cutting off an input from the power supply.

Next, a seventh invention is a control circuit for controlling a synchronous rectification type DC-DC converter provided with a main switch and a synchronous rectification switch. An overvoltage detecting means for detecting that the voltage is an overvoltage; a first control signal for turning off the main switch and a second control signal for turning on the synchronous rectifying switch when the overvoltage detecting means detects the overvoltage. And control means for outputting the second control signal. According to an eighth aspect of the present invention, there is provided a synchronous rectifier comprising: a main switch; a synchronous rectifying switch; an inductor connected to the main switch; and a capacitor connected to the inductor and smoothing an output voltage from the inductor. A control circuit for controlling a DC-DC converter of a system, wherein an overvoltage detecting means for detecting that an output voltage of the DC-DC converter is an overvoltage, and when the overvoltage detecting means detects an overvoltage. 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. The ninth
The present invention is a control circuit for controlling a DC-DC converter of a synchronous rectification system including a main switch and a switch for synchronous rectification, wherein an output voltage of the DC-DC converter is an overvoltage. Overvoltage detection means for detecting, and control means for forcibly turning off the main switch and forcibly turning on the synchronous rectification switch when the overvoltage detection means detects an overvoltage. You may. In the seventh to ninth aspects of the present invention, the overvoltage detection means may output a detection signal when detecting that the output voltage of the DC-DC converter is an overvoltage. In response, the control means:
When a detection signal is output from the overvoltage detection means, the detection signal is stored, a first control signal for turning off the main switch, and a second control signal for turning on the synchronous rectification switch. A memory circuit for outputting a signal may be provided. Further, when the main switch fails, the control means may output a second control signal for turning on the synchronous rectification switch, thereby short-circuiting the input from the power supply.

In a tenth aspect, the present invention provides a main switch, a switch for synchronous rectification, 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 controlling a DC-DC converter of a synchronous rectification system comprising: an overvoltage detection unit for detecting that an output voltage of the DC-DC converter is an overvoltage; and Control means for forcibly turning off the main switch and forcibly turning on the synchronous rectification switch when the switch is detected. The control circuit according to the tenth aspect may further include feedback means for performing feedback control of the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter at a constant value.

Next, an eleventh invention is a control circuit for controlling a DC-DC converter of a synchronous rectification system including a main switch and a switch for synchronous rectification. Receiving means for receiving a signal, a first control signal for turning off the main switch and a second control for turning on the synchronous rectifying switch when the receiving means receives the stop request signal; Control means for outputting a signal. still,
The control means may output the second control signal for turning on the synchronous rectification switch when the main switch fails, thereby causing the input from the power supply to be short-circuited. In a twelfth aspect, a main switch includes:
A synchronous rectification type DC-DC converter comprising a synchronous rectification switch, an inductor connected to the main switch, and a capacitor connected to the inductor and smoothing an output voltage from the inductor. A control circuit for receiving a stop request signal for DC-DC conversion processing; a first control signal for turning off a visit main switch when the receiving means receives the stop request signal; Control means for outputting a second control signal for turning on the rectifying switch. The control means may output the second control signal for turning on the synchronous rectification switch when the main switch fails, thereby causing the input from the power supply to be short-circuited. A thirteenth invention is a control circuit for controlling a synchronous rectification type DC-DC sliding door device including a main switch and a synchronous rectification switch, which receives a stop request signal for DC-DC conversion processing. And a control unit for forcibly turning off the main switch and forcibly turning on the synchronous rectification switch when the receiving unit receives the stop request signal. Good. A fourteenth invention is a synchronous rectification system including a main switch, a synchronous rectification switch, an inductor connected to the main switch, and a capacitor connected to the inductor and smoothing an output voltage from the inductor. In a control circuit for controlling the DC-DC converter, receiving means for receiving a stop request signal for DC-DC conversion processing, and when the receiving means receives the stop request signal, the main switch is forcibly turned off. Control means for forcibly turning on the synchronous rectification switch.

[0048] Incidentally, <br/> stop request signal according to the eleventh fourteenth invention described above, the DC - may be a signal indicating that the output voltage of the DC converter is overvoltage. Further, the control circuit according to the eleventh to fourteenth aspects further includes feedback means for performing feedback control of the main switch and the synchronous rectification switch in order to keep the output voltage of the DC-DC converter at a constant value. You may.

Next, a fifteenth invention is a control circuit for controlling a synchronous rectification type DC-DC converter provided with a main switch and a synchronous rectification switch. A receiving unit for receiving a signal, and when the receiving unit receives a stop request signal, turning off the main switch and turning on the synchronous rectification switch to stop the output of the DC-DC converter. Control means may be provided.

Next, a sixteenth invention is a control circuit for controlling a DC-DC converter of a synchronous rectification system comprising a main switch and a switch for synchronous rectification. A voltage input terminal for inputting a voltage, an overvoltage detection unit that outputs a detection signal when detecting that a voltage input to the voltage input terminal exceeds a predetermined voltage, and when the overvoltage detection unit outputs a detection signal, Clamping means for turning off the main switch and turning on the synchronous rectification switch to clamp the output of the DC-DC converter to a ground level may be provided.

[0051]

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 according to the present invention. In the figure, the same components and components as those in the related art are given the same names and reference numerals.

DC-DC converter
Is a device that is provided between a battery (not shown) as a power supply and a load and that supplies a constant voltage from the battery to the load.

(DC-DC CONVERTE
R) Configuration) The DC-DC converter according to the first embodiment includes a fuse F1 and a control circuit C.
TL, a main switching transistor Tr1, a synchronous rectification transistor Tr2, a diode D1, a choke coil L1, a capacitor C1, a voltage comparator IC1, a power source e1, a capacitor C2, and a capacitor C3 for generating a reference voltage e1.

(DC-DC converter)
R) Connection of Circuits Constituting R) Here, the connection of the above components will be described. The fuse F1 is provided in 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 to the signal line 2
4 and connected to the control circuit CTL.

The above main switching transistor T
r1 is, for example, a MOS-FET (Metal-type) having three terminals of a source terminal, a drain terminal, and a gate terminal.
Oxide Semiconductor Field Effect Transistor). In this case, the signal line 14 is connected to the drain terminal of the main switching transistor Tr1. The signal line 1 is connected to the source terminal of the main switching transistor Tr1. 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
Among 9, the signal line 31 near the fuse F1 is connected to the ground via the capacitor C3. The signal line 17 among the four signal lines 31, 17, 18, and 19 is connected to the voltage comparator IC1. This voltage comparator IC1
Has, for example, a non-inverting input terminal, an inverting input terminal, and an output terminal. 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
9 are connected to the control circuit CTL. A signal line 18a is connected in the middle of the signal line 18. This signal line 18a is connected to the ground via the capacitor C2.

The above four signal lines 31, 17, 18, 1
The signal line 19 near the main switching transistor Tr1 out 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.

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

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

The signal line 3 near the choke coil L1 among the two signal lines 2 and 3 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, two signal lines 4 and 5 are connected in the middle of the signal line 15 connecting the choke coil L1 and the load. Among the two signal lines 4, 5, the signal line 4 near the choke coil L1 is connected to the control circuit CTL. This signal line 4 is connected to a DC-DC converter (DC-DC CO
NVERTER) is a signal line for feeding back the output voltage FB to the control circuit CTL.

Of the two signal lines 4 and 5, the signal line 5 near the load is connected to the ground via the capacitor C1. (Function of Circuit Constituting DC-DC Converter) Next, the function of each of the above-described components will be described.

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

(Power source e1) The power source e1 generates a reference voltage e1 of a voltage to be input to a 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.
And outputs a signal OV indicating the result of the comparison.
The signal OV output from the voltage comparator IC1 is connected to the signal line 2
3 to the control circuit CTL.

For example, the voltage comparator IC1 subtracts the reference voltage e1 from the voltage Vi, and the result of the subtraction is "0".
If it is below, a low-level signal is output, and if the subtraction result is a positive value, a high-level signal is output.

(Capacitor C2) The capacitor C2 stores 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 receives 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 the 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

The main switching transistor T
r1 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 disconnects the signal line 14 and the signal line 1.

(Choke coil L1) Choke coil L
Reference numeral 1 denotes a voltage conversion coil. (Diode D1) The diode D1 is a freewheel diode that releases the energy stored in the choke coil L1 to the output side when the main switching transistor Tr1 is off.

(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 according to the input signal DL. It 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 between the drain terminal and the source terminal, and connects between the signal line 2 and the signal line 26.

The synchronous rectification transistor Tr2 is
If the voltage from the control circuit CTL is not applied to the gate terminal, the gate terminal is turned off, the connection between the drain terminal and the source terminal is cut off, and the connection between the signal line 2 and the signal line 26 is cut off.

In this example, the synchronous rectification transistor T
r2 is a freewheel switch circuit for outputting the energy stored in the choke coil L1 when the main switching transistor Tr1 is off.

For example, the synchronous rectification transistor Tr2
Turns on when the voltage applied to the diode D1 is in the forward direction (a state in which the signal line 2 is connected to the signal line 26), and turns off when the voltage applied to the diode D1 is in the reverse direction. This is the state (the state where the signal line 2 and the signal line 26 are disconnected). At this time, the voltage drop of the diode D1 is reduced.

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

(Control Circuit CTL) The control circuit CTL includes:
In addition to the above-mentioned signal lines 4, 19, 23, 18, 24 and 25, an external ON command value or an OFF command value and an external target voltage Vref are input. The target voltage Vref from the outside is obtained by a DC-DC converter (DC-DCCONVERT
ER) is a reference voltage of a voltage to be output.

The control circuit CTL includes a voltage comparator I
According to signal OV from C1, output voltage FB input via signal line 4, and target voltage Vref from the outside,
The on / off state of the main switching transistor Tr1 and the synchronous rectification transistor Tr2 is switched.

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

(Power Supply 7) The power supply 7 supplies operating power to a circuit constituting the control circuit CTL when an external ON command value is input. In addition, the power supply 7 stops supplying the operating power to the circuit configuring the control circuit CTL when an off command value is input from the outside.

(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.

(Division resistance R2 / R3) Division resistance R2 / R
Reference numeral 3 is connected to the signal line 4 so that an output voltage FB of a DC-DC converter is input. This dividing resistor R2 / R3 is connected to the output voltage FB
Is a sense resistor for sensing the voltage value of

The voltage value sensed by the dividing resistors 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,
An error amplifier circuit that receives an external target voltage Vref and 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 connected to the triangular wave oscillator 8
The conversion triangle wave output from is input. In addition, PWM
The non-inverting input terminal of the comparator 9 inputs a signal output from the error amplifier ERA.

Then, 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. Then, while the value obtained by the subtraction indicates a negative value (while the signal output from the triangular wave oscillator 8 is larger than the signal output from the error amplifier ERA1), the PWM comparator 9 keeps the High level. Output a signal.

While the value obtained by the subtraction indicates 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 PWM comparator 9 A low-level signal is output.

The signal (Hi) output from the PWM comparator 9
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 a main switching transistor Tr1
Is supplied to the drive-1 (10), and the voltage for driving the synchronous rectification transistor Tr2 is supplied to the drive-1 (10).
2 (11).

(Synchronous rectification control circuit 13) The synchronous rectification control circuit 13 receives a signal output from the PWM comparator 9. Then, the synchronous rectification control circuit 13 controls the PWM comparator 9
, The synchronous rectification is performed by switching between the ON state and the OFF state of the synchronous rectification transistor Tr2.

For example, the synchronous rectification control circuit 13 has a PWM
When a low-level signal from the comparator 8 is input, H
It outputs a high-level signal. Further, the synchronous rectification control circuit 13 outputs a Low level signal when receiving a High level signal from the PWM comparator 8.

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 set terminal S of the flip-flop FF receives the signal OV output from the voltage comparator IC1. At this time, the flip-flop FF
The signal input to the set terminal S is stored.

A reset terminal R of the flip-flop FF receives an external ON command value or an external OFF command value. When an ON command value or an OFF command value is input to the reset terminal R, the signal stored in the flip-flop FF is reset to a Low level signal.

Further, 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 a signal stored in the flip-flop FF.

For example, a DC-DC converter (DC-DC CONV
When the input voltage Vi of the ERTER is equal to or lower than the reference voltage e1, 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 FF stores the low-level signal input to the set terminal S, and the output terminal Q outputs the low-level signal stored in the flip-flop FF.

Further, a DC-DC converter (DC-DC converter)
When the input voltage Vi of the TER) exceeds the reference voltage e1 (when the input voltage Vi becomes overvoltage), the set terminal S of the flip-flop FF outputs a High-level signal as the signal OV from the voltage comparator IC1. input. 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 in the flip-flop FF.

(OR circuit OR2) OR circuit OR2
Is the signal from the PWM comparator 9 and the flip-flop FF
And a signal indicating the result of the logical sum is input to the drive-1 (10).

For example, a DC-DC converter (DC-DC CONV
When the input voltage Vi of (ERTER) is equal to or lower than the reference voltage e1, the OR circuit OR2 receives a low-level signal from the output terminal Q of the flip-flop FF. In this case, the OR circuit OR2 outputs the signal from the PWM comparator 9 as it is. As a result, when the input voltage of the DC-DC converter is equal to or lower than the reference voltage e1, the drive-1 (10)
It operates according to the signal from the WM comparator 9.

A DC-DC converter (DC-DC CONVER
When the input voltage of the flip-flop FF is higher than the reference voltage e1 (when the input voltage is in an overvoltage state), the OR circuit OR2 outputs the H signal from the output terminal Q of the flip-flop FF.
A high-level signal is input. in this case,
The OR circuit OR2 outputs a high-level signal regardless of the signal from the PWM comparator 9. As a result, if the input voltage of the DC-DC converter (DC-DC converter) is in an overvoltage state, drive-1 (1
0) operates according to the signal from the flip-flop FF regardless of the signal from the PWM comparator 9.

(OR circuit OR1) OR circuit OR1
Performs a logical OR operation of a signal output from the synchronous rectification control circuit 13 and a 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 CONV
ERTER) is equal to or less than the reference voltage e1,
The OR circuit OR1 outputs Lo from the flip-flop FF.
A w-level signal is input. 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 input voltage Vi is equal to or less than the reference voltage e1, the drive-1 (10)
It operates according to the signal from the synchronous rectification control circuit 13.

A DC-DC converter (DC-DC converter)
When the input voltage Vi of (TER) becomes higher than the reference voltage e1 (when the input voltage Vi becomes an overvoltage), the OR circuit OR1 inputs a 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. As a result, if the input voltage of the DC-DC converter becomes overvoltage, 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) switches between the ON state and the OFF state of the main switching transistor Tr1 according to the signal from the OR circuit OR2.

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

When the drive-1 (10) receives a 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 is turned off.
To the off state.

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

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

When the drive-2 (11) receives a Low-level signal from the OR circuit OR1, the drive-2 (11) outputs
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 (DC-DC CONVERTE) according to the present embodiment will be described.
The function and effect of R) will be described.

(1) DC-DC converter
When the DC-DC converter is operating normally, that is, when the DC-DC converter is operating normally,
When the input voltage Vi of the (CONVERTER) indicates a normal voltage value, the input voltage Vi becomes sufficiently smaller than the reference voltage e1, and the signal OV from the voltage comparator IC1 is Lo.
The signal indicates the w 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. Then, the flip-flop FF stores the input Low-level signal.

When the flip-flop FF stores the Low level signal, the output terminal Q of the flip-flop FF
Outputs a low-level signal. 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.

Also, the dividing resistor R2 / R of the control circuit CTL
3 is a DC-DC converter (DC-DC converter) via a signal line 4.
CONVERTER) output voltage FB. The divided resistors R2 / R3 sense the input output voltage FB,
The sensed voltage value is input to the error amplifier ERA1.

The error amplifier ERA1 to which the voltage value from the division resistors R2 / R3 is input amplifies and outputs an error between the voltage value from the division resistors 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 has an error amplifier ERA1
, While the conversion triangle wave from the triangle wave oscillator 8 is input. When the error from the error amplifier ERA1 is smaller than the conversion triangular wave from the triangular wave oscillator 8, the PWM comparator 9 outputs a high-level signal.

The PWM comparator 9 has an error amplifier E
If the error from RA1 is larger than the conversion triangle wave from the triangle 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.

The synchronous rectification control circuit 13 to which the signal from the PWM comparator 9 has been input, outputs the signal from the PWM comparator 9 to Hi.
When the signal is a gh level signal, a low level signal is output. On the other hand, the synchronous rectification control circuit 13 includes the PWM comparator 9
Is a low level signal, a high level signal is output. The signal output from the synchronous rectification control circuit 13 is input to the OR circuit OR1.

As described above, the OR circuit OR2 outputs the Low level signal from the flip-flop FF and the PW
The signal (high-level signal or low-level signal) from the M comparator 9 is input, and the OR circuit OR1 outputs the low-level signal from the flip-flop FF.
Signal from the synchronous rectification control circuit 13 (H
(High level signal or Low level signal)
Will be entered.

The OR circuit OR2 has 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 outputs the H signal from the PWM comparator 9.
When a high-level signal is input, a high-level signal is output. The OR circuit OR2 outputs a low-level signal when receiving a low-level signal from the PWM comparator 9.

The signal output from the OR circuit OR2 is
Drive-1 (10) is input. OR circuit OR2
Drive-1 (10) to which the signal from the OR gate OR is input, if the signal from the OR circuit OR2 is a Low-level signal,
The power supply to the main switching transistor Tr1 is stopped. At this time, the main switching transistor Tr1 is turned off and disconnects the signal line 14 and the signal line 1.

The drive-1 (10) operates as follows if the signal from the OR circuit OR2 is a High level signal.
The power from the charge pump circuit 12 is supplied to the main switching transistor Tr1. At this time, the main switching transistor Tr1 is turned on, and connects between the signal line 14 and the signal line 1.

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 is used to output the signal (High-level signal or Low-level signal) from the synchronous rectification control circuit 13. Signal) as it is.

The signal output from the OR circuit OR1 is
Drive-2 (11) is input. OR circuit OR1
Drive-2 (11), which has received the signal from the OR gate OR1, if the signal from the OR circuit OR1 is a low-level signal,
The power supply to the synchronous rectification transistor Tr2 is stopped. At this time, the synchronous rectification transistor Tr2 is turned off, and disconnects the signal line 2 and the signal line 26.

The drive-2 (11) outputs the signal from the OR circuit OR1 if it is a High level signal.
The power from the charge pump circuit 12 is supplied to the transistor for synchronous rectification Tr2. At this time, the synchronous rectification transistor Tr2 is turned on, and the signal lines 2 and 26
Connect between

(2) DC-DC converter
TER) When the input voltage of the DC-DC converter becomes overvoltage, the input voltage Vi becomes the reference voltage e.
Since it becomes larger than 1, the signal OV from the voltage comparator IC1 becomes a signal indicating a High level.

High output from voltage comparator IC1
The level signal is supplied to the flip-flop F of the control circuit CTL.
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 flip-flop FF
Outputs the stored high-level signal from the output terminal Q.

Hi output from flip-flop FF
The gh level signal is obtained by the OR circuit OR of the control circuit CTL.
2 and the OR circuit OR1. Further, the division resistance R2 / R3 of the control circuit CTL is connected to the output voltage FB of the DC-DC converter via the signal line 4.
Enter Then, the divided 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 divided resistors R2 / R3 is input amplifies and outputs an error between the voltage value from the divided resistors R2 / R3 and an external target voltage Vref. The error output from the error amplifier ERA1 is input to the PWM comparator 9.

The PWM comparator 9 has an error amplifier ERA1
, While the conversion triangle wave from the triangle wave oscillator 8 is input. When the error from the error amplifier ERA1 is smaller than the conversion triangular wave from the triangular wave oscillator 8, the PWM comparator 9 outputs a high-level signal.

The PWM comparator 9 has an error amplifier E
If the error from RA1 is larger than the conversion triangle wave from the triangle 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.

The synchronous rectification control circuit 13 which has received the signal from the PWM comparator 9 outputs the signal from the PWM comparator 9 to Hi.
When the signal is a gh level signal, a low level signal is output. On the other hand, when the signal from the PWM comparator 9 is a low-level signal, the synchronous rectification control circuit 13
Output level signal. The signal output from the synchronous rectification control circuit 13 is input to the OR circuit OR1.

As described above, the OR circuit OR2 outputs the high-level signal from the flip-flop FF and the PW
A signal (high-level signal or low-level signal) from the M comparator 9 is input. Further, the OR circuit OR1 receives the High-level signal from the flip-flop FF and the signal (High-level signal or Low-level signal) from the synchronous rectification control circuit 13.

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

High output from OR circuit OR2
The level signal is input to drive-1 (10).
Drive-1 (10), which has received the High-level signal from the OR circuit OR2, 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.

Since the OR circuit OR1 receives the High-level signal from the flip-flop FF, it is related to the signal (High-level signal or Low-level signal) from the synchronous rectification control circuit 13. No H
This outputs a high-level signal.

High output from OR circuit OR1
The level signal is input to the drive-2 (11).
Drive-2 (11) that has received the High-level signal from the OR circuit OR1 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 connects between the signal line 2 and the signal line 26.

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

Therefore, when the fuse F1 is blown, the components of the DC-DC converter (DC-DC converter), in particular, the capacitor C3 provided at the input of the DC-DC converter are provided. Can be prevented from being applied with an excessive voltage, and burning of the capacitor C3 can be prevented.

Further, the DC-DC converter according to the present embodiment is used when the power supply of the control circuit CTL cannot generate driving power for the main switching transistor Tr1 and the synchronous rectification transistor Tr2. The main switching transistor Tr1 and the synchronous rectification transistor Tr2 are driven by the power stored in the capacitor C2. Thus, the DC-DC converter can guarantee the operation of the main switching transistor Tr1 and the synchronous rectification transistor Tr2 until the fuse F1 is blown.

Incidentally, the main switching transistor Tr
Of course, the drive power supply for the first and synchronous rectification transistor Tr2 is not limited to the capacitor C2. Also,
The DC-DC converter according to the present embodiment (DC-DC CONV
According to ERTER), it is not necessary to use an organic capacitor having a high withstand voltage as the capacitor C3, and a fuse for preventing burning is not required, and the number of components is reduced.

Further, since the fuse for preventing the capacitor C3 from burning is not required, the resistance in the DC-DC converter is reduced, and the DC-DC converter is reduced. Conversion efficiency is improved.

<DC-DC CONVERTE
R) Other Embodiments> A DC-DC converter according to the first embodiment includes a voltage comparator IC1.
And the power supply e1 are provided separately from the control circuit CTL.
As shown in FIGS. 3 and 4, the voltage comparator IC1 and the power supply e1 may be provided in the control circuit CTL.

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

The division resistors R4 / R5 sense 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 supply 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 becomes an overvoltage state, the voltage Vi in the overvoltage state becomes the divided 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 has a divided resistor R4 / R5
The reference voltage from the power supply e1 is subtracted from the voltage value from.
At this time, since the voltage value from the division 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. Thus, the voltage comparator IC
1 and the power supply e1 can be provided in the control circuit CTL to obtain the same effect as in the first embodiment.

In the example of FIGS. 3 and 4, the control circuit CTL
Has a built-in power supply e2 for generating the target voltage Vref. Thus, by adopting the configuration as shown in FIGS. 3 and 4, the same effect as that of the first embodiment can be obtained, and the circuit configuration of the DC-DC converter is simplified. can do. <Embodiment 2> FIG. 5 is a diagram showing a DC-DC converter according to a second embodiment of the present invention. In the figure, the same components and components as those in the first embodiment are given the same names and reference numerals.

DC-DC converter (DC-DC converter)
Is provided between a battery as a power supply and a load. (Configuration of DC-DC Converter) The DC-DC converter according to the first embodiment (DC-DC converter)
ERTER) includes a control circuit CTL, a main switching transistor Tr1, a transistor for synchronous rectification Tr2, a diode D1, a choke coil L1, a capacitor C1, a voltage comparator IC2, and a power supply e for generating a reference voltage e3.
3 is provided.

(DC-DC converter)
R) Connection Configuration of Circuits Constituting) First, the connection configuration of the above 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
Connected to control circuit CTL via signal line 24.

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 connected in the middle of the signal line 14. This signal line 19 is connected to the control circuit CT
L. 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 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 a signal line 25 and to the ground via a signal line 26.

Of the 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.

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 signal line for inputting the voltage value CS input to the resistor R1 to the control circuit CTL.

Also, three signal lines 4, 5, and 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. This signal line 4 is a signal line for feeding back the voltage value FB output from the DC-DC converter (DC-DC converter) to the control circuit CTL.

The middle signal line 5 among the three signal lines 4, 5, 21 is connected to ground via a 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
Connected to the non-inverting input terminal of C2. The inverting input terminal of the voltage comparator IC2 is connected to a power supply e3 via a signal line 28. Further, the above-described voltage comparator IC2
Is connected to the control circuit CTL via the signal line 29.

(DC-DC converter)
R) Functions of the Circuits Constituting) Next, the functions of each of the above components will be described. The description of the same components as those in the first embodiment is omitted.

(Resistance R1) The resistance R1 is a sense resistor for sensing an output current value of a DC-DC converter.

(Power source e3) The power source e3 generates a reference voltage e3 of the voltage output from the DC-DC converter.

(Voltage comparator IC2) Voltage comparator IC2
Inputs the output voltage of the DC-DC converter (DC-DC converter) via the signal line 21 and simultaneously inputs the reference voltage e3 from the power supply e3. And a voltage comparator IC
Reference numeral 2 compares an output voltage of a DC-DC converter and a reference voltage e3 from a power supply e3, and outputs a signal OV indicating a result of the comparison.

For example, the voltage comparator IC2 subtracts the reference voltage e3 from the output voltage of the DC-DC converter (DC-DC converter), and if the result of the subtraction is "0" or less, it is Low.
A level signal is output, and if the subtraction result is a positive value, Hig is output.
An h-level signal is output.

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

The control circuit CTL includes a voltage comparator I
The main switching transistor Tr1 and the synchronous rectification according to the signal OV from C2, the voltage value FB input via the signal line 4, and the target voltage Vref of the voltage to be output from the DC-DC converter. The on / off state of the transistor for use Tr2 is switched.

Here, the internal configuration of the control circuit CTL will be described. (Configuration of Control Circuit CTL) As shown in FIG. 6, the control circuit CTL employs a pulse width modulation method (PWM method), and includes a power supply 7, a triangular wave oscillator 8, a PWM comparator 9, a charge pump circuit 12, and the like. , Synchronous rectification control circuit 13,
Flip-flop FF, drive-1 (10), and
Drive-2 (11) is provided. Further, the control circuit CTL includes a dividing resistor R2 / R3, an error amplifier ERA
1, ERA2, AND circuit AND1, and OR circuit OR1.

(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 connected to the triangular wave oscillator 8
The conversion triangle wave output from is input. In addition, PWM
The non-inverting input terminal of the comparator 9 inputs a signal output from the error amplifier ERA1.

Then, 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. Then, while the value obtained by the subtraction indicates a negative value (while the signal output from the triangular wave oscillator 8 is larger than the signal output from the error amplifier ERA1), the PWM comparator 9 keeps the High level. Output a signal.

Further, while the value obtained by subtraction indicates 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 PWM comparator 9 A low-level signal is output.

The signal output from the PWM comparator 9 is input to the AND circuit AND1 and the synchronous rectification control circuit 13. (Error amplifier ERA2) The error amplifier ERA2 is provided with an output voltage FB of a DC-DC converter.
Is input via the signal line 4, and at the same time, the voltage value CS input to the resistor R 1 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 obtains the DC-DC converter (DC-DC CO).
NVERTER) is an error amplifying circuit that measures the current value output from the NVERTER.

The voltage value output from error amplifier ERA 2 is input to synchronous rectification control circuit 13. (Synchronous rectification control circuit 13) The synchronous rectification control circuit 13
The signal output from the WM comparator 9 and the error amplifier ERA
2 and the signal output from the second input. The synchronous rectification control circuit 13 is a circuit that performs synchronous rectification by switching between the ON state and the OFF state of the synchronous rectification transistor Tr2 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 has a PWM
A high-level signal is output only when a low-level signal from the comparator 8 is input and the signal from the error amplifier ERA2 is equal to or less than a predetermined 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 two output terminals, a non-inverted output terminal Q and an inverted output terminal * Q.

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 an ON command value or an OFF command value is input to the reset terminal, the signal stored in the flip-flop FF is reset to a 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 CONV
When the output voltage FB is lower than the reference voltage e3, 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 FF 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 CONVER
When the output voltage FB of the TER) exceeds the reference voltage e3 (when the output voltage FB becomes overvoltage), the set terminal S of the flip-flop FF outputs a High-level signal as the signal OV from the voltage comparator IC2. input. In this case, the flip-flop FF stores the High-level signal input to the set terminal S, and the non-inverted output terminal Q outputs the Hi-level signal stored in the flip-flop FF.
gh level signals are output.

Inverting output terminal of flip-flop FF * Q
Are connected to an AND circuit AND1. The inverted 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 low-level signal, the output terminal FB of the inverting output terminal * Q is equal to or lower than the reference voltage e3 of the DC-DC converter. Then, a High level signal is output. The inverted output terminal * Q is connected to the signal OV stored in the flip-flop FF.
Is a high-level signal (if the output voltage FB of the DC-DC converter exceeds the reference voltage e3), a low-level signal is output.

(AND circuit AND1) AND circuit AND
1 receives the signal output from the PWM comparator 9 and the signal output from the inverted output terminal * Q of the flip-flop FF. The AND circuit AND1 is connected to the PWM comparator 9
And a 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
Input to (10).

For example, a DC-DC converter (DC-DC CONV
ERTER) is equal to or lower than the reference voltage e3,
The AND circuit AND1 receives a High-level signal from the inverted 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.

A DC-DC converter (DC-DC converter)
When the output voltage FB of the TER) becomes higher than the reference voltage e3 (when the output voltage FB becomes an overvoltage), the AND circuit AND1 outputs a low-level signal from the inverted output terminal * Q of the flip-flop FF. Will be entered.
In this case, the AND circuit AND1 outputs a Low-level signal regardless of the signal from the PWM comparator 9. As a result, when the output voltage FB becomes 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 a signal output from the synchronous rectification control circuit 13 and a signal output from the non-inverting output terminal Q of the flip-flop FF. The OR 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 CONV
ERTER) is equal to or lower than the reference voltage e3,
The OR circuit OR1 receives a 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 is equal to or lower than the reference voltage e3, the drive-2 (11) operates according to the signal from the synchronous rectification control circuit 13.

A DC-DC converter (DC-DC CONVER
When the output voltage FB of the TER) becomes higher than the reference voltage e3 (when the output voltage FB becomes overvoltage), the OR circuit OR1 outputs a High-level signal from the non-inverting output terminal Q of the flip-flop FF. Will be entered.
In this case, the OR circuit OR1 is connected to the synchronous rectification control circuit 13
Will output a high-level signal regardless of the signal from. As a result, when the output voltage FB becomes 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) corresponds to a signal from the AND circuit AND1,
The on / off state of the main switching transistor Tr1 is switched.

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

When the drive-1 (10) receives a Low-level signal from the AND circuit AND1, the drive-1 (10) stops supplying power to the main switching transistor Tr1, and turns off the main switching transistor T1.
r1 is turned off.

(Operation and Effect of Second Embodiment) Hereinafter, a DC-DC converter according to the present embodiment (DC-DC CONVERTE
The function and effect of R) will be described.

(1) DC-DC converter
When the DC-DC converter is operating normally, that is, when the DC-DC converter is operating normally,
When the output voltage FB of CONVERTER indicates a normal voltage value, the output voltage FB becomes sufficiently smaller than the reference voltage e3, and the voltage comparator IC2 outputs a low-level signal.

The Low-level signal output from the voltage comparator IC2 is connected to the flip-flop FF of the control circuit CTL.
Is input to the set terminal S. 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 inverted output terminal * Q of the flip-flop FF outputs a High level signal.

Non-inverting output terminal Q of flip-flop FF
Is output from the OR circuit OR
1 is input. 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 signal.
Input to (11).

Drive-2 (11) is provided with an OR circuit OR
The synchronous rectification transistor Tr2 is switched between an on state and an off state in accordance with a signal from the synchronous rectification control circuit 13; As a result, drive-2
(11) The synchronous rectification transistor Tr2 may be turned on while the main switching transistor Tr1 is off and the diode D1 is discharging the energy accumulated in the choke coil L1 to the output side. it can.

The High-level signal output from the inverted output terminal * Q of the flip-flop FF is input to the AND circuit AND1. In this case, the AND circuit AN
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
Drive-1 (10) is input.

Drive-1 (10) is a logical product circuit AN
The on / off state of the main switching transistor Tr1 is switched according to a signal from D1, that is, a signal from the PWM comparator 9. As a result, the 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 may input the output voltage FB of the DC-DC converter. become unable. At this time, the control circuit CT
No voltage is applied to the L divided resistors R2 / R3. As a result, the value of the signal output from the division 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 error amplifier ERA1 becomes smaller than the triangular wave from triangular wave oscillator 8, 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, since the output voltage of the DC-DC converter is sufficiently lower than the reference voltage e3 of the power supply e3, the voltage comparator IC2 is set to L
It outputs an ow level signal.

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

As described above, the AND circuit AND1 is
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 logical product circuit AND1 is set to Hig.
An h-level signal is output. The high-level signal output from the AND circuit AND1 is the drive-1 (1
0).

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, and turns on the main switching transistor Tr1.

By the way, since the signal line 4 is disconnected, the control circuit CTL uses the DC-DC converter (DC-D
The control for increasing the output voltage FB as described above is continued without being able to recognize the output voltage FB of C CONVERTER). As a result, the actual output voltage of the DC-DC converter increases, and an overvoltage state may occur.

[0209] DC-DC converter
When the output voltage falls into an overvoltage state, the output voltage becomes higher than the reference voltage e3.
gh level signals are output. Voltage comparator I
The high-level signal output from C2 is input to the set terminal S of the flip-flop FF of the control circuit CTL.

The flip-flop FF stores a 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.
gh level signal and the inverted output terminal * Q is Lo
A w-level signal is output.

The non-inverting output terminal Q of the flip-flop FF
Is 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 stream control circuit 13. The high-level signal output from the OR circuit OR1 is the drive-2 signal.
Input to (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 inverted 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 irrespective 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 to which Low-level signal is input
1 (10) is the main switching transistor Tr1
Is stopped, and the main switching transistor Tr1 is turned off.

As described above, the DC-DC converter (DC-DC converter)
When the output voltage of the CONVERTER is in an overvoltage state, the main switching transistor Tr1 is forcibly turned off and 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 CONVERTE
The output voltage R) is clamped to the ground voltage (0 V) connected to the signal line 26.

Therefore, a DC-DC converter (DC-DC CONV
ERTER) can be prevented from being applied to a load. Further, according to the DC-DC converter according to the present embodiment, it is not necessary to use a high-withstand voltage organic capacitor as the smoothing capacitor C1, and it is not necessary to use a fuse for preventing burnout. Thus, the number of components is reduced.

Further, since the fuse for preventing the capacitor C1 from burning is not required, the resistance in the DC-DC converter is reduced, and the DC-DC converter is reduced. Conversion efficiency is improved.

(3) Main Switching Transistor T
When a short-circuit fault occurs in r1 When a short-circuit fault occurs in the main switching transistor Tr1, the signal line 14 and the signal line 1 are connected, so that the output voltage of the DC-DC converter is obtained. May fall into an overvoltage state.

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

At this time, as described in the above (2), the control circuit CTL controls the synchronous rectification transistor Tr.
2 is forcibly turned on, and the DC-DC converter (DC-D
Clamp the output voltage of C CONVERTER to ground level. With this, DC-DC converter (DC-DC CONVER
TER) can be prevented from being applied to the load.

Furthermore, as described in the first embodiment, if a fuse is provided in the middle of the signal line 14, the voltage applied to the DC-DC converter (DC-DC converter) will The circuit is short-circuited via the line 14, the main switching transistor Tr1, the signal line 1, the signal line 2, and the synchronous rectification transistor Tr2. At this time, the fuse is blown by the short-circuit current.

As a result, the DC-DC converter (DC-DC CO
The voltage applied to the NVERTER is cut off in a very short time, and the DC-DC converter (DC-DC CONVERTE
R) can be prevented from being applied to the load at an early stage.

Therefore, according to the DC-DC converter according to the present embodiment, when an overvoltage condition occurs, the DC-DC converter (DC-DC converter) is activated.
R) The circuit and the load can be reliably protected.

Further, according to the DC-DC converter according to the present embodiment, 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 components is reduced.

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

<DC-DC CONVERTE
R) Other Embodiments> A DC-DC converter according to the present embodiment includes a voltage comparator IC2 and a power supply e3 separately from the control circuit CTL.
The voltage comparator IC2 and the power supply e3 may be built in the control circuit CTL as shown in FIGS.

In this case, signal line 21 is directly connected to control circuit CTL as shown in FIG. Further, as shown in FIG. 8, the control circuit CTL includes a dividing resistor R6 / R7 connected to the signal line 21, a voltage comparator IC2 connected to the dividing resistor R6 / R7, and a voltage comparator IC2. And a power supply e3 to be connected.

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

[0230] The inverting input terminal of the voltage comparator IC2 is connected to the power supply e3 via the signal line 28. Further, the output terminal of the voltage comparator IC2 is connected to the set terminal S of the flip-flop FF via the signal line 29.

In the case where the control circuit CTL is configured as described above, when the output voltage of the DC-DC converter becomes an overvoltage state, the output voltage in the overvoltage state is applied to the dividing resistors R6 / R7 of the control circuit CTL. Is entered.

The dividing resistors R6 / R7 sense an output voltage value in an 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 has a divided resistor 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
It outputs a high-level signal.

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

Therefore, even if the voltage comparator IC2 and the power supply e3 are incorporated in the control circuit CTL, the same effects as in the second embodiment can be obtained. <Third Embodiment> FIG. 9 is a diagram showing a third embodiment of the DC-DC converter according to the present invention. In the figure, the same components as those in the first and second embodiments are given the same names and reference numerals.

(DC-DC CONVERTE
R) Configuration) DC-DC converter
Are a fuse F1, a voltage comparator IC1, a power supply e1, a capacitor C3, a capacitor C2, an OR circuit OR3, a control circuit CTL, a main switching transistor Tr1,
It includes a transistor for synchronous rectification Tr2, a diode D1, a choke coil L1, a resistor R1, a capacitor C1, a voltage comparator IC2, and a power supply e3.

(DC-DC CONVERTE
R) Connection of Circuits Constituting R) Here, the connection of the above components will be described. The fuse F1 is provided in the signal line 14 connecting the battery and the main switching transistor Tr1.

The main switching transistor Tr 1 connected to the battery via the signal line 14 is connected to the choke coil L 1 via the signal line 1 and
4 and 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. A resistor R1 connected to the choke coil L1 via the signal line 15
Is connected to a load via a signal line 16.

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

The above four signal lines 31, 17, 18, 1
Among 9, the signal line 31 near the fuse F1 is connected to the ground via the capacitor C3. The signal line 17 among the four signal lines 31, 17, 18, and 19 is connected to the voltage comparator IC1. This voltage comparator IC1
Has, for example, a non-inverting input terminal, an inverting input terminal, and an output terminal. 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 four signal lines 31, 17, 18, 1
9 are connected to the control circuit CTL. A signal line 18a is connected in the middle of the signal line 18. This signal line 18a is connected to the ground via the capacitor C2.

The above four signal lines 31, 17, 18, 1
The signal line 19 near the main switching transistor Tr1 out 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.

The signal line 2 near the main switching transistor Tr1 of the two signal lines 2 and 3 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 to the ground via the signal line 26 at the same time.

The signal line 3 near the choke coil L1 among the two signal lines 2 and 3 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.

Furthermore, 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 connected to a DC-DC converter (DC-DC CONVERTE
R) is a signal line for inputting the voltage value CS output from R) to the control circuit CTL.

In the middle of the signal line 16 connecting the resistor R1 and the load, 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. This signal line 4 is a signal line for feeding back the voltage value FB output from the DC-DC converter (DC-DC converter) to the control circuit CTL.

The middle signal line 5 among the three signal lines 4, 5, 21 is connected to the ground via a 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
Connected to the non-inverting input terminal of C2. The inverting input terminal of the voltage comparator IC2 is connected to a power supply e3 via a signal line. Further, the above-described voltage comparator IC2
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 is connected to the voltage comparator IC2 via the signal line 29. This OR circuit OR3 is a circuit having two input terminals and one output terminal. In this case, the two input terminals are connected to the signal line 23 and the signal line 29, respectively.
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, 4 and simultaneously receives an external ON command value or OFF command value. The target voltage Vref is input.

(DC-DC CONVERTE
R) Functions of the Circuits Constituting) Next, the functions of each of the above components will be described. The description of the components described in the first and second embodiments will be omitted.

(OR circuit OR3) OR circuit OR3
Inputs a signal output from the voltage comparator IC1 and a signal output from the voltage comparator IC2. The OR circuit OR3 is composed of a voltage comparator IC1 and a voltage comparator IC2.
When a high-level signal is input from at least one of the DC-DC converters (DC-DC CONV
When the input voltage of the ERTER is higher than the reference voltage e1, or when a DC-DC converter (DC-DC CONVERTE
When the output voltage of R) becomes higher than the reference voltage e3, a high-level signal indicating that an overvoltage state has occurred is output.

The OR circuit OR3 is connected to the voltage comparator I
When a low-level signal is input from both the circuit of C1 and the voltage comparator IC2, that is, the input voltage of the DC-DC converter is equal to or less than the reference voltage e1 and the DC-DC Converter (DC-DC CONVERTE
When the output voltage of R) is equal to or lower than the reference voltage e3, Lo
A w-level signal is output.

(Operation and Effect of Third Embodiment) Hereinafter, a DC-DC converter (DC-DC CONVERTE) according to the third embodiment will be described.
The function and effect of R) will be described.

(1) DC-DC converter
When the DC-DC converter is operating normally, that is, when the DC-DC converter is operating normally,
When the input voltage of the DC-DC converter is equal to or less than the reference voltage e1 and the output voltage of the DC-DC converter is equal to or less than the reference voltage e3, the voltage comparator IC1
And the voltage comparator IC2 will output a low level signal.

The 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 connected to the flip-flop FF of the control circuit CTL.
Is input to the set terminal S. Then, the flip-flop FF stores the input Low-level signal. At this time, the output terminal Q of the flip-flop FF outputs a 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 a low level signal is input 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 provided with an OR circuit OR
The synchronous rectification transistor Tr2 is switched between an on state and an off state in accordance with a signal from the synchronous rectification control circuit 13; As a result, drive-2
(11) The synchronous rectification transistor Tr2 may be turned on while the main switching transistor Tr1 is off and the diode D1 is discharging the energy accumulated in the choke coil L1 to the output side. it can.

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

Drive-1 (10) is provided with an OR circuit OR
The main switching transistor Tr1 is switched between an on state and an off state in accordance with a signal from the second switching transistor Tr1, that is, a signal from the PWM comparator 9. As a result, the 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 changes from the voltage value from the error amplifier ERA1. The main switching transistor Tr1 can be turned off when the voltage is low.

(2) DC-DC converter
TER) When the input voltage of the DC-DC converter becomes an overvoltage state When the voltage input to the DC-DC converter becomes an overvoltage, the input voltage becomes larger than the reference voltage e1. The signal output from IC1 is 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 CONVER
TER) is smaller than the reference voltage e3.
The signal output from the voltage comparator IC2 is a Low level signal. L output from the voltage comparator IC2
The low level signal is input to the OR circuit OR3.

As described above, the OR circuit OR3 receives 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 is a High level signal. OR circuit OR3
Is 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 connected to the input Hi.
gh level signals will be stored. The output terminal Q of the flip-flop FF is connected to the flip-flop F
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 the OR circuit 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-2 which has input the High level signal from 1
(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 connects between the signal line 2 and the signal line 26.

Also, Hig from flip-flop FF is output.
The OR circuit OR2 to which the signal of the h level has been input has the PWM
A high level signal is output irrespective of the signal from the comparator 9.

High output from OR circuit OR2
The level signal is input to drive-1 (10).
Drive-1 (10), which has received the High-level signal from the OR circuit OR2, 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, a DC-DC converter (DC-DC CO
NVERTER), 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,
The signal is applied to the ground through 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, so that the components of the DC-DC converter (DC-DC converter), in particular, the capacitor C3 provided at the input portion of the DC-DC converter are provided. Can be prevented from being applied with an excessive voltage, and burning of the capacitor C3 can be prevented.

According to the DC-DC converter according to the present embodiment, the capacitor C3
It is not necessary to use an organic capacitor having a high withstand voltage, and a fuse for preventing burning is not required, and the number of components is reduced.

Further, since the fuse for preventing burning of the capacitor C3 is not required, the resistance in the DC-DC converter is reduced, and the DC-DC converter is reduced. Conversion efficiency is improved.

(3) DC-DC converter (DC-DC CONVER
If the output voltage of the DC-DC converter is in an overvoltage state, the output voltage is higher than the reference voltage e3. Outputs a high-level signal. The high-level signal output from the voltage comparator IC2 is input to the OR circuit OR3 via the signal line 29.

On the other hand, a DC-DC converter (DC-DC CONVER
Since the input voltage of TER) is 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 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. Hig output from this OR circuit OR3
The h-level signal is input to the control circuit CTL.

At this time, as described in the above (1), the control circuit CTL forcibly turns on the main switching transistor Tr1 and the transistor for synchronous rectification Tr2, and turns on the DC-DC converter (DC-DC converter). CONVERTE
R), 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.

As a result, a DC-DC converter (DC-DC CO
NVERTER) is cut off,
It is possible to prevent an overvoltage from being applied to a load of a DC-DC converter.

Therefore, according to the DC-DC converter according to the present embodiment, when the output voltage of the DC-DC converter becomes an overvoltage state, the DC-DC converter -DC converter (DC-DC CONVERTE
R) The circuit and the load can be reliably protected.

Further, according to the DC-DC converter according to the present embodiment, it is not necessary to use a high withstand voltage organic capacitor as the smoothing capacitor C1, and the fuse for preventing burnout is used. Is unnecessary, and the number of components is reduced.

Further, since the fuse for preventing burning of the smoothing capacitor C1 is not required, the resistance in the DC-DC converter is reduced, and the DC-DC converter (DC-DC converter) is reduced. DC CONVERTER) conversion efficiency is improved. <Embodiment 4> FIG. 10 is a diagram showing a fourth embodiment of a DC-DC converter according to the present invention. In the figure, the same components as those in the third embodiment are given the same names and reference numerals.

(DC-DC CONVERTE device)
R) Configuration) DC-DC converter
Is a fuse F1, a voltage comparator IC1, a power supply e1, a capacitor C3, a capacitor C2, a control circuit CTL, a main switching transistor Tr1, a synchronous rectification transistor Tr2, a diode D1, a choke coil L1, a resistor R1, a capacitor C1, and a voltage comparator. It has an IC2 and a power supply e3.

(DC-DC CONVERTE device)
R) Connection of Circuits Constituting R) Here, the connection of the above components will be described. Here, only a connection mode different from the above-described third embodiment will be described.

The output terminal of the voltage comparator IC1 is connected to the signal line 2
3 and 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.

[0285] Other connection modes are the same as those in the third embodiment.
Is the same as (Function of Circuit Constituting DC-DC Converter) Next, the function of each of the above-described components will be described. The description of the same components as those in the third embodiment is 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

The control circuit CTL includes a voltage comparator IC
2 and is connected via a signal line 29, and receives the signal OV2 output from the voltage comparator IC2.
In this case, the control circuit CTL uses the DC-DC converter (DC-DC converter) as the signal OV1 from the voltage comparator IC1.
When a signal (high-level signal) indicating that the input voltage of the TER) 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. To

The control circuit CTL includes a voltage comparator IC
As a signal OV2 from the DC-DC converter (DC-D
When a signal (High level signal) indicating that the output voltage of the C CONVERTER is in an overvoltage state is input, the main switching transistor Tr1 is forcibly turned off and the synchronous rectification transistor Tr2 is forcibly turned on. And a DC-DC converter
TER) output voltage is clamped to ground level.

Here, the control circuit C for realizing the above functions
The internal configuration of the TL will be described. (Configuration 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), division resistance R2 / R3, error amplifiers ERA1, ERA2, AND circuit AND1, OR circuit OR1, OR circuit OR4,
And an OR circuit OR5 (flip-flop FF1) flip-flop FF1
Has two input terminals, a set terminal S and a reset terminal R, and an output terminal Q.

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 external ON command value or external OFF command value. When an ON command value or an OFF command value is input to the reset terminal R, the flip-flop FF1
The stored content is reset to store a Low level signal.

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 connected to a flip-flop FF
1 outputs the stored signal.

For example, a DC-DC converter (DC-DC CONV
ERTER) is less than or equal to 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 FF1 stores the Low-level signal input to the set terminal S. Then, the output terminal Q of the flip-flop FF1
Outputs the low-level signal stored in the flip-flop FF1.

Also, a DC-DC converter (DC-DC CONVER
TER) exceeds the reference voltage e1 (when the input voltage becomes overvoltage), the flip-flop FF1
Is set to a signal OV1 from the voltage comparator IC1.
, A high level signal is input. In this case, the flip-flop FF1 is connected to the H input to the set terminal S.
The high level signal is stored. Then, the output terminal Q of the flip-flop FF1 outputs a 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-inverted output terminal Q and an inverted output terminal * Q.

A set terminal S of the flip-flop FF2
Inputs the signal OV2 from the voltage comparator IC2. A reset terminal R of the flip-flop FF2 receives an external ON command value or an OFF command value. When an ON command value or an OFF command value is input to the reset terminal, the signal stored in the flip-flop FF2 becomes Low.
It is reset to the 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 CONV
ERTER) is less than or equal to 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 FF2 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 FF2. .

A DC-DC converter (DC-DC CONVER
TER) exceeds the reference voltage e3 (when the output voltage becomes overvoltage), the flip-flop FF2
Is set to a signal OV2 from the voltage comparator IC2.
, A high level signal is input. In this case, the flip-flop FF2 is connected to the Hi terminal input to the set terminal S.
gh-level signal, and the non-inverted output terminal Q is connected to the High-level signal stored in the flip-flop FF2.
An h-level signal is output.

The inverted output terminal of flip-flop FF2 *
Q is connected to the AND circuit AND1. The inverted 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 is connected to a DC-DC converter (DC-DC converter).
R) if the output voltage is less than or equal to the reference voltage e3), High
A level signal will be output. Also, the inverted output terminal * Q is connected to the output terminal of the flip-flop FF2 if the signal OV2 is a high-level signal (if the output voltage of the DC-DC converter exceeds the reference voltage e3). ), A Low level signal is output.

(AND circuit AND1) AND circuit AND
1 inputs the signal output from the PWM comparator 9 and the signal output from the inverted 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 result of the calculation.
The signal output from the AND circuit AND1 is input to the OR circuit OR4.

For example, a DC-DC converter (DC-DC CONV
When the output voltage of the ERTER) is equal to or lower than the reference voltage e3, the AND circuit AND1 outputs the signal from the PWM comparator 9 and the High from the inverted output terminal * Q of the flip-flop FF2.
And level signal. In this case, the AND circuit AN
D1 outputs the signal from the PWM comparator 9 as it is.

Also, a DC-DC converter (DC-DC CONVER
TER) becomes higher than the reference voltage e3 (when the output voltage becomes overvoltage), the AND circuit AN
D1 receives the signal from the PWM comparator 9 and the Low-level signal from the inverted output terminal * Q of the flip-flop FF2. In this case, the AND circuit AND
1 outputs a low-level signal irrespective of the signal from the PWM comparator 9.

(OR circuit OR4) OR circuit OR4
Inputs a signal output from the AND circuit AND1 and a signal output from the output terminal Q of the flip-flop FF1. This OR circuit OR4 is provided with an AND circuit AND4.
The logical sum of the signal from the output terminal 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
Drive-1 (10) is input.

For example, a DC-DC converter (DC-DC CONV
ERTER) is equal to or lower than the reference voltage e1, and
When 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 same signal as the signal output from the PWM comparator 9) and the output terminal Q of the flip-flop FF1. Is input. In this case, the OR circuit OR4
Is a signal from the AND circuit AND1, that is, PWM.
The signal from the comparator 9 is output as it is.

[0307] DC-DC converter
Is higher than the reference voltage e1 and the output voltage is equal to or lower than the reference voltage e3, the OR circuit OR
4 is a signal from the AND circuit AND1 (PWM comparator 9).
And the High level signal from the output terminal Q of the flip-flop FF1. In this case, the OR circuit OR4
A high-level signal is output regardless of the signal from the AND circuit AND1.

[0308] DC-DC CONVERTER
Is equal to or lower than the reference voltage e1 and the output voltage is higher than the reference voltage e3, the OR circuit O
R4 receives the Low signal from the AND circuit AND1 and the Low-level signal from the flip-flop FF1. In this case, the OR circuit OR4 outputs Lo
A w-level signal is output.

(OR circuit OR1) OR circuit OR1
Inputs a signal output from the synchronous rectification control circuit 13 and a signal output from the output terminal Q of the flip-flop FF1. Then, the OR 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 CONV
ERTER) is less than or equal to the reference voltage e1,
The OR circuit OR1 receives the signal from the synchronous rectification control circuit 13 and the Low-level signal from the flip-flop FF1. In this case, the OR circuit OR1
Outputs the signal from the synchronous rectification control circuit 13 as it is.

[0311] DC-DC CONVERTER
Is larger than the reference voltage e1,
The OR circuit OR1 receives the signal from the synchronous rectification control circuit 13 and the high-level signal from the flip-flop FF1. In this case, the OR circuit OR
1 is H regardless of the signal from the synchronous rectification control circuit 13.
It outputs a high-level signal.

(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 connected to the OR circuit OR5.
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 CONV
ERTER) is equal to or lower than the reference voltage e1, and
When the output voltage is equal to or lower than the reference voltage e3, the OR circuit OR5 outputs a High-level signal from the OR circuit OR1 and Lo from the output terminal Q of the flip-flop FF2.
and a w-level signal. In this case, the OR circuit OR5 outputs a High level signal.

[0314] DC-DC converter
Is higher than the reference voltage e1 and the output voltage is equal to or lower than the reference voltage e3, the OR circuit OR5
Is a High level signal from the OR circuit OR1,
A low-level signal from the output terminal Q of the flip-flop FF2 is input. In this case, the OR circuit OR5 outputs a High level signal.

[0315] DC-DC converter
Is equal to or lower than the reference voltage e1 and the output voltage is higher than the reference voltage e3, the signal from the OR circuit OR1 (the same signal as the signal output from the synchronous rectification control circuit 13) And a 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 between the ON state and the OFF state of the main switching transistor Tr1 according to the signal from the OR circuit OR4.

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

When the drive-1 (10) receives a Low-level signal from the AND circuit AND1, the drive-1 (10) stops supplying power to the main switching transistor Tr1, and turns off the main switching transistor T1.
r1 is turned off.

(Operation and Effect of Fourth Embodiment) Hereinafter, a DC-DC converter according to the present embodiment (DC-DC CONVERTE
The function and effect of R) will be described.

(1) DC-DC converter
When the DC-DC converter is operating normally, that is, when the DC-DC converter (DC-DC converter) is operating normally,
When the input voltage of the DC-DC converter is equal to or less than the reference voltage e1 and the output voltage of the DC-DC converter is equal to or less than the reference voltage e3, the voltage comparator IC1
And the voltage comparator IC2 will output a low level signal.

The Low-level signal output from the voltage comparator IC1 is connected to the flip-flop FF of the control circuit CTL.
1 is input to the set terminal S. Also, a voltage comparator IC
2 is output from the control circuit CT
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 connected to the input Low.
The w-level signal is stored. 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 which has received the Low level signal from the voltage comparator IC2 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 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 receives the signal from the PWM comparator 9 while receiving the High level signal from the output terminal * Q of the flip-flop FF2.
At this time, the AND circuit AND1 outputs the signal from the PWM comparator 9 as it is. AND circuit AN
The signal output from D1 is input to the OR circuit OR4.

As described above, the OR circuit OR4 outputs 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) output from the OR circuit OR4
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 between the ON state and the OFF state of the main switching transistor Tr1 according to the signal from the PWM comparator 9.

Also, a logical sum circuit OR to which a Low level signal is input 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.

As described above, the OR circuit OR5 outputs 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 is connected to the OR circuit OR1.
, That is, the same signal as the signal output from the synchronous rectification control circuit 13. The signal output from the OR circuit OR5 (the synchronous rectification control circuit 13
Is the same signal as the signal output from drive-2)
Input to (11). As a result, drive-2 (1
In 1), the on / off state of the synchronous rectification transistor Tr2 can be switched according to a signal from the synchronous rectification control circuit 13.

(2) DC-DC converter (DC-DC CONVER
TER), the voltage input to the DC-DC converter (DC-DC converter) is overvoltage, the voltage comparator IC1
Outputs a high-level signal. Further, since the output voltage of the DC-DC converter is equal to or lower than the reference voltage e3, the voltage comparator IC2 outputs a Low-level signal.

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

The flip-flop FF1 to which the high-level signal from the voltage comparator IC1 has been input is input to the flip-flop FF1.
The high-level signal is stored. Then, 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 which has received the Low level signal from the voltage comparator IC2 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 low-level signal is input to the OR 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 receives the signal from the PWM comparator 9 while receiving the High level signal from the output terminal * Q of the flip-flop FF2. In this case, the AND circuit AND1 is connected to the PWM comparator 9
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.

As described above, the OR circuit OR4 is connected to 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 the input terminal. In this case, the OR circuit OR4 is connected to the AND circuit AND4.
Thus, a high-level signal is output regardless of the signal from the signal 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.

The OR circuit OR1 receives a High-level signal from the output terminal Q of the flip-flop FF1, and receives a 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 outputs Hi
gh level signal is output. 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-DC converter)
When the input voltage of the CONVERTER is in an overvoltage state, the main switching transistor Tr1 and the synchronous rectification transistor Tr2 are forcibly turned on.

As a result, the DC-DC converter (DC-DC CO
NVERTER), 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,
The signal is applied to the ground through 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, so that the components of the DC-DC converter (DC-DC converter), in particular, the capacitor C3 provided at the input of the DC-DC converter (DC-DC converter). Can be prevented from being applied with an excessive voltage, and burning of the capacitor C3 can be prevented.

Furthermore, according to the DC-DC converter according to the present embodiment, the capacitor C
The burnout prevention fuse 3 is unnecessary, and the number of components is reduced.

In addition, since the fuse for preventing the capacitor C3 from burning is not required, the resistance in the DC-DC converter is reduced, and the DC-DC converter is reduced. Conversion efficiency is improved.

(3) When the Signal Line 4 is Disconnected When the signal line 4 is disconnected, the DC-DC converter (DC-DC CONVERTE) is used as described in the second embodiment.
The output voltage of R) may fall into an overvoltage state.

[0343] DC-DC converter
When the output voltage falls into an overvoltage state, the output voltage becomes higher than the reference voltage e3.
gh level signals are output.

On the other hand, a DC-DC converter (DC-DC CONVER
Since the input voltage of TER) 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 connected to the set terminal S of the flip-flop FF1 of the control circuit CTL.
Is input to The high-level signal output from the voltage comparator IC2 is input to the set terminal S of the flip-flop FF2 of the control circuit CTL.

The flip-flop FF1 to which the Low-level signal from the voltage comparator IC1 has been input is connected to the input Low.
The w-level signal is stored. 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 that has received the High-level signal from the voltage comparator IC2 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 receives a low-level signal from the output terminal * Q of the flip-flop FF2 and receives a signal from the PWM comparator 9. In this case, the AND circuit AND1 is connected to the PWM comparator 9
Will output a low-level signal regardless of the signal from. L output from the AND circuit AND1
The low 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 outputs Lo
It outputs a signal of w level. As a result, the drive-1 (10) operates the main switching transistor Tr1 regardless of the signal output from the PWM comparator 9.
To the off state.

The OR circuit OR1 receives a low-level signal from the output terminal Q of the flip-flop FF1, and 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.

As described above, the OR circuit OR5 outputs 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). At this time, the OR circuit OR5 becomes the OR circuit OR5.
A high-level signal is output irrespective 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-DC
When the output voltage of the CONVERTER is in an overvoltage state, the main switching transistor Tr1 is forcibly turned off and 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 CONVERTE
The output voltage R) is clamped to the ground voltage (0 V) connected to the signal line 26.

Therefore, a DC-DC converter (DC-DC CONV
ERTER) can be prevented from being applied with an overvoltage to the load, and at the same time, a DC-DC converter (DC-DC CONV
ERTER), in particular, an overvoltage can be prevented from being applied to the smoothing capacitor C1.

Further, according to the DC-DC converter according to the present embodiment, 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 components is reduced.

Further, since the fuse for preventing the capacitor C1 from burning is not required, the resistance in the DC-DC converter is reduced, and the DC-DC converter is reduced. Conversion efficiency is improved.

(4) Main Switching Transistor T
When r1 causes a short-circuit fault When the main switching transistor Tr1 causes a short-circuit fault, the signal line 14 and the signal line 1 are connected, so that the output voltage of the DC-DC converter is obtained. May fall into an overvoltage state.

When the output voltage falls into an overvoltage state due to a short-circuit failure of the main switching transistor Tr1, the output voltage becomes higher than the reference voltage e3.
C2 will output a High level signal.

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

At this time, the control circuit CTL forcibly turns off the main switching transistor Tr1 and simultaneously turns on the synchronous rectification transistor Tr2 at the same time as described in the above (2). Do. However, since the main switching transistor Tr1 has a short-circuit fault, the DC-DC converter (DC-DC CO
NVERTER) is short-circuited via the fuse F1, the signal line 14, the main switching transistor Tr1, the signal line 1, the signal line 2, and the synchronous rectification transistor Tr2. At this time, the fuse F1 is blown by the short-circuit current.

As a result, a DC-DC converter (DC-DC CO
The voltage applied to the NVERTER is cut off in a very short time, and the DC-DC converter (DC-DC CONVERTE
R) can prevent the overvoltage from being applied to the load, and at the same time, the DC-DC converter (DC-DC CONVERTE
Overvoltage can be prevented from being applied to the components of R).

Further, according to the DC-DC converter according to the present embodiment, it is not necessary to use a high withstand voltage organic capacitor as the smoothing capacitor C1, and the fuse for preventing burnout is used. Is unnecessary, and the number of components is reduced.

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

[0363]

The DC-DC converter (DC) according to the present invention
According to -DC CONVERTER), when the output voltage of the DC-DC converter is in an overvoltage state, the first switch element and the second switch element (main switching transistor and synchronous rectification transistor) are overvoltage protected. By using as a circuit, it is possible to prevent an overvoltage from being applied to the components of the DC-DC converter or the load of the DC-DC converter without complicating the circuit configuration. As a result, it is possible to provide a technique for preventing smoke and ignition of an organic capacitor used in a DC-DC converter, preventing overvoltage of an output voltage without complicating a circuit, and reducing the size and reliability of the apparatus. Can be improved.

As a result, smoke and ignition of the organic capacitor used in the DC-DC converter can be prevented,
It is possible to reduce the size of a DC-DC converter and improve conversion efficiency.

[Brief description of the drawings]

FIG. 1 shows a DC-DC converter (DC-DC CO) according to the present invention.
FIG. 2 is a diagram showing a configuration of Embodiment 1 of the present invention.

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

FIG. 3 shows a DC-DC converter (DC-DC CO) according to the present invention.
NVERTER) is a diagram showing the configuration of another embodiment.

FIG. 4 shows a DC-DC converter of FIG.
(R) is a diagram showing an internal configuration of a control circuit CTL corresponding to (R).

FIG. 5 shows a DC-DC converter (DC-DC CO) according to the present invention.
NVERTER) diagram showing the configuration of Embodiment 2

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

FIG. 7 shows a DC-DC converter according to the present invention.
NVERTER) is a diagram showing the configuration of another embodiment.

8 is a DC-DC converter shown in FIG.
(R) is a diagram showing an internal configuration of a control circuit CTL corresponding to (R).

FIG. 9 shows a DC-DC converter (DC-DC CO) according to the present invention.
NVERTER) diagram showing the configuration of Embodiment 3

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

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

FIG. 12 shows a conventional DC-DC converter (DC-DC CONVERTE
Diagram showing the configuration of R)

[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 comparison CTL Control circuit L1 Choke coil F1 Fuse e1 Power supply e2 Power supply C1 Capacitor C2 Capacitor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-59763 (JP, A) JP-A-4-54864 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/155 H02H 3/20

Claims (43)

(57) [Claims] An accumulator for accumulating electric power from a power supply; a first switch element for switching connection and disconnection of the power supply and the accumulator; and an accumulator provided between the accumulator and a ground. A second switch element for switching between connection and disconnection of the means and the ground; and the first switch element and the second switch element.
A synchronously rectifying type DC-DC converter, comprising: a control unit that alternately connects the battery and keeps the output voltage from the storage unit at a constant value, and monitors the output voltage from the storage unit. An overvoltage detection unit that outputs a signal when the output voltage exceeds a predetermined voltage value; and when the signal from the overvoltage detection unit is input, the first switch element is maintained in a disconnected state. A synchronous rectification type DC-DC converter, comprising: a clamp unit for connecting the second switch element to a connection state and clamping an output voltage from the storage unit to a ground level. Wherein said overvoltage detection means compares the reference voltage generating means for generating a reference voltage, a pre Kimoto reference voltage and the output voltage from said storage means, said output voltage is greater than the reference voltage When it gets old
2. The DC-DC converter according to claim 1 , further comprising: a voltage comparison unit that outputs the signal. 3. A failure of the first switch element in a short-circuit state.
Then, the second switch element is brought into a connected state.
Means for short-circuiting the voltage from the power supply.
DC synchronous rectification according to claim 1, wherein obtaining - DC converter. 4. The DC-DC converter of a synchronous rectification system according to claim 3, further comprising a cut-off means for cutting off an input from said power supply by the power short-circuited by said short-circuit means. 5. The fuse according to claim 4, wherein said shut-off means is a fuse which is blown by electric power short-circuited by said short-circuit means.
The DC-DC converter of the synchronous rectification system described in the above. 6. The synchronous rectification type DC-DC converter according to claim 1, further comprising a cut-off means provided between said power supply and said first switch element to cut off an input from said power supply. 7. When the first switch element fails, the clamp means short-circuits the power from the power supply by bringing the second switch element into a connection state. 7. An input from said power source is cut off using power short-circuited by a clamp means.
The DC-DC converter of the synchronous rectification system according to the above. 8. A storage means for storing power from a power supply, a first switch for switching connection and disconnection of the power supply and the storage means, and a storage means disposed between the storage means and ground, A second switch for switching between connection and disconnection between the first switch element and the ground, and the first switch element and the second switch element.
Control means for alternately connecting to keep the output voltage from the storage means at a constant value; detection means for detecting that the output voltage of the storage means exceeds a predetermined voltage value; A synchronous rectification type DC-DC converter, comprising: clamp means for maintaining the first switch in a disconnected state and connecting the second switch in response to detection of the means. 9. The detecting means compares a reference voltage generating means for generating a reference voltage with an output voltage of the accumulating means, and an 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 when necessary. 10. A short-circuit means for short-circuiting power from a power supply by forcibly bringing a second switch into a connected state when the first switch fails in a short-circuit state. DC-DC converter of synchronous rectification system. 11. The synchronous rectification type DC-DC converter according to claim 10, further comprising a cut-off means for cutting off an input from said power supply. 12. The DC-DC converter according to claim 11, wherein said cutoff means is a fuse. 13. A synchronous rectification type DC-DC converter according to claim 8, further comprising a cut-off means provided between said power supply and said first switch element for cutting off an input from said power supply. 14. When the first switch element fails, the clamp means short-circuits the power from the power supply by bringing the second switch element into a connection state. 2. An input from said power source is cut off using power short-circuited by a clamp means.
3. The DC-DC converter of the synchronous rectification method according to 3. 15. A storage means for storing power from a power supply, a first switch element for switching between connection and disconnection of said power supply and said storage means, and said storage means provided between said storage means and ground. A second switch element for switching connection and disconnection of the means and the ground, and the first switch element and the second switch element.
Alternately in the connected state, the DC of the first control means and the synchronous rectification method having the output voltage from said storage means to maintain a constant value - in the control circuit for a DC converter, the storage Monitoring an output voltage from the means to detect that the output voltage has exceeded a predetermined voltage value; anda detecting that the overvoltage detection means has detected that the output voltage has exceeded a predetermined voltage value. the with the first switching element is maintained in the disconnected state and the second switching element to the connection state, the control circuit comprising a second control means, a to the output voltage to the ground level from the storage means. 16. An overvoltage detecting means, comprising: a reference voltage generating means for generating a reference voltage; and comparing the reference voltage with an output voltage from the storage means, wherein the output voltage is larger than the reference voltage. 16. The control circuit according to claim 15, further comprising: a voltage comparison unit that outputs a signal. 17. A storage means for storing power from a power supply, a first switch element for switching connection and disconnection of the power supply and the storage means, and a storage means provided between the storage means and ground, A second switch element for switching connection and disconnection of the means and the ground, and the first switch element and the second switch element.
Alternately in the connected state, the DC of the first control means and the synchronous rectification method having the output voltage from said storage means to maintain a constant value - in the control circuit for a DC converter, the storage Detecting means for monitoring the output voltage from the means to detect that the output voltage has exceeded a predetermined voltage value; and maintaining the first switch element in a disconnected state in response to the detection by the detecting means. a control circuit and a second control means for said second switching element connected. 18. The detecting means for comparing a reference voltage generating means for generating a reference voltage with an output voltage of the accumulating means, wherein an output voltage of the accumulating means is larger than the reference voltage. 18. The control circuit according to claim 17, further comprising: a voltage comparison unit that outputs a signal. 19. A DC-DC converter of a synchronous rectification system, wherein a main switch, a switch for synchronous rectification alternately connected to the main switch, and an output voltage of the DC-DC converter is an overvoltage. An overvoltage detecting means for detecting that an overvoltage has been detected, a first control signal for keeping the main switch off and a second control signal for turning on the synchronous rectifying switch when the overvoltage detecting means detects an overvoltage. And a control means for outputting the control signal of the synchronous rectification type DC-DC converter. 20. A DC-DC converter of a synchronous rectification system, wherein a main switch, a switch for synchronous rectification alternately connected to the main switch, and an output voltage of the DC-DC converter is an overvoltage. Overvoltage detection means for detecting that, when the overvoltage detection means detects overvoltage, while forcibly maintaining the main switch off, control means for forcibly turning on the synchronous rectification switch, DC-DC converter of a synchronous rectification system comprising: 21. The synchronous rectification type DC-DC converter according to claim 19, further comprising: an inductor connected to the main switch; and a capacitor connected to the inductor and 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 outputs 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 a control signal of
The DC-DC converter of the synchronous rectification system described in the above. 24. The synchronous rectification system according to claim 19, further comprising feedback means for performing feedback control of said main switch and said synchronous rectification switch so as to keep the output voltage of said DC-DC converter constant. DC-DC converter. 25. The control means, wherein when the main switch fails in a short-circuit state, by outputting a second control signal to turn on the synchronous rectification switch,
24. The DC-DC converter according to claim 23, wherein an input from a power supply is short-circuited. 26. The DC-DC converter of the synchronous rectification system according to claim 19, further comprising a cut-off means provided between said main switch and said power supply for cutting off an input from said power supply. 27. A main switch, and said main switch
DC synchronous rectification scheme and a synchronous rectification switch which is alternately connected state with - in the control circuit for controlling a DC converter, the DC - the output voltage of the DC converter is overvoltage Overvoltage detection means for detecting, and a first control signal for keeping the main switch off and a second control for turning on the synchronous rectification switch when the overvoltage detection means detects an overvoltage. Control means for outputting a signal; 28. A main switch, and said main switch
A synchronous rectification type DC-DC switch comprising: a synchronous rectification switch alternately connected to the main switch; an inductor connected to the main switch; and a capacitor connected to the inductor and smoothing an output voltage from the inductor. In a control circuit for controlling the DC converter, an overvoltage detection unit that detects that the output voltage of the DC-DC converter is an overvoltage, and when the overvoltage detection unit detects an overvoltage, the main switch Control means for outputting a first control signal for keeping the switch off and a second control signal for turning on the synchronous rectification switch. 29. A main switch, and said main switch
DC synchronous rectification scheme and a synchronous rectification switch which is alternately connected state with - in the control circuit for controlling a DC converter, the DC - the output voltage of the DC converter is overvoltage A control comprising: an overvoltage detecting means for detecting; and a control means for forcibly turning on the synchronous rectification switch while forcibly maintaining the main switch off when the overvoltage detecting means detects an overvoltage. circuit. 30. A main switch, and the main switch
A synchronous rectification type DC-DC switch comprising: a synchronous rectification switch alternately connected to the main switch; an inductor connected to the main switch; and a capacitor connected to the inductor and smoothing an output voltage from the inductor. In a control circuit for controlling the DC converter, an overvoltage detection unit that detects that the output voltage of the DC-DC converter is an overvoltage, and when the overvoltage detection unit detects an overvoltage, the main switch Control means for forcibly keeping the switch off and forcibly turning on the synchronous rectification switch. 31. The apparatus according to claim 27, wherein said overvoltage detecting means outputs a detection signal when detecting that the output voltage of said DC-DC converter is an overvoltage. Control circuit. 32. When the detection signal is output from the overvoltage detection means, the control means stores the detection signal, and outputs a first control signal for turning off the main switch and the synchronous rectification signal. The control circuit according to claim 31, further comprising a memory circuit that outputs a second control signal for turning on the switch. 33. The control circuit according to claim 31, wherein when the main switch fails, the control circuit outputs a second control signal for turning on the synchronous rectification switch to short-circuit the input from the power supply. The control circuit according to any one of claims 27 to 29. 34. The apparatus according to claim 27, further comprising feedback means for performing feedback control of said main switch and said synchronous rectification switch so as to maintain the output voltage of said DC-DC converter at a constant value. 3. The control circuit according to 1. 35. A main switch, and said main switch
In the control circuit for controlling a DC converter, DC - - a DC synchronous rectification scheme and a synchronous rectification switch, which is in connection state alternately receiving means for receiving a stop request signal of the DC conversion process Control means for outputting a first control signal for keeping the main switch off and a second control signal for turning on the synchronous rectification switch when the receiving means receives the stop request signal; And a control circuit comprising: 36. A main switch, and said main switch
A synchronous rectification type switch comprising: a synchronous rectification switch alternately connected to the main switch; an inductor connected to the main switch; and a capacitor connected to the inductor and smoothing an output voltage from the inductor.
In a control circuit for controlling the DC converter, receiving means for receiving a stop request signal for DC-DC conversion processing, and a second circuit for keeping the main switch off when the receiving means receives the stop request signal. Control means for outputting a first control signal and a second control signal for turning on the synchronous rectification switch. 37. A main switch, and said main switch
DC synchronous rectification scheme and a synchronous rectification switch which is in a connected state alternately and - in the control circuit for controlling the DC Henfusuma device, DC - receiving means for receiving a stop request signal of the DC conversion process And a control means for forcibly maintaining the main switch off when the receiving means receives the stop request signal and forcibly turning on the synchronous rectification switch. 38. A main switch, and said main switch
A synchronous rectification type DC-DC comprising a synchronous rectification switch alternately connected to the main switch, an inductor connected to the main switch, and a capacitor connected to the inductor and smoothing an output voltage from the inductor. In a control circuit for controlling the converter, receiving means for receiving a stop request signal for DC-DC conversion processing, and when the receiving means receives the stop request signal, the main switch is forcibly kept off and And control means for forcibly turning on the synchronous rectification switch. 39. The control circuit according to claim 35, wherein the stop request signal is a signal indicating that an output voltage of the DC-DC converter is an overvoltage. 40. The apparatus according to claim 35, further comprising feedback means for performing feedback control of said main switch and said synchronous rectification switch so as to maintain the output voltage of said DC-DC converter at a constant value. Control circuit. 41. The control means for short-circuiting an input from the power supply by outputting a second control signal for turning on the synchronous rectification switch when the main switch fails. The control circuit according to claim 35 or 36. 42. A main switch, and said main switch
In the control circuit for controlling a DC converter, DC - - a DC synchronous rectification scheme and a synchronous rectification switch, which is in connection state alternately receiving means for receiving a stop request signal of the DC conversion process Control means for stopping the output of the DC-DC converter by maintaining the main switch off and turning on the synchronous rectification switch when the receiving means receives the stop request signal. Control circuit. 43. A main switch, and said main switch
DC synchronous rectification scheme and a synchronous rectification switch which is alternately connected state with - in the control circuit for controlling a DC converter, the DC - voltage input terminal for inputting the output voltage of the DC converter When detecting that the voltage input to the voltage input terminal exceeds a predetermined voltage, an overvoltage detection unit that outputs a detection signal, and when the overvoltage detection unit outputs a detection signal, the main switch is turned on. A control means for clamping the output of the DC-DC converter to a ground level by keeping the switch off and turning on the synchronous rectification switch.