JP2002010627A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter which has an overcurrent protection circuit which enables to interrupt an overcurrent by accurately detecting it without getting influence of environmental temperature, and a high conversion efficiency. SOLUTION: The DC-DC converter comprises connecting both terminals of DC circuit consisting of a first switch and a detection resistor to a control circuit. By detecting a current which flows the control circuit when the current exceeds a specified value, the first switch is off-operated and a second switch is on-operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter for converting a DC input power to a predetermined DC output power, and more particularly to an overcurrent protection circuit in a DC-DC converter.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram showing an example of a conventional DC-DC converter. As shown in FIG.
The DC converter includes a first switching circuit 101 connected to a DC input power supply, and a second switching circuit provided at a subsequent stage of the first switching circuit 101 and connecting a positive electrode and a negative electrode.
The first switching circuit 101 and the second switching circuit 102 are on / off controlled by a control circuit 103. The control circuit 103 controls the on / off operation of the first switching circuit 101, and controls the first switching circuit 10
The on / off operation of the second switching circuit 102 is controlled in synchronization with the on / off operation of the first switching circuit 102. A commutating diode 106 is connected to the conventional DC-DC converter in parallel with the second switching circuit 102, and a smoothing circuit including a reactor 104 and a capacitor 105 is provided.

As shown in FIG. 7, in a conventional DC-DC converter, in order to constantly monitor an output current, a detection resistor 109 for detecting the current is provided in a reactor 10.
4 is connected to the output side. Both ends of the detection resistor 109 are connected to a current detection signal line 103 derived from the control circuit 103.
a, 103b. In a conventional DC-DC converter, the control circuit 103 is configured to output a predetermined DC voltage by controlling the ON time of the first switching circuit 101 and the second switching circuit 102. Further, the control circuit 103 constantly detects the current flowing through the detection resistor 109 for current detection, and turns off the first switching circuit 101 when the current flowing through the detection resistor 109 exceeds a predetermined current value. hand,
The overcurrent is prevented from flowing inside the DC-DC converter and on the output side.

The conventional DC-DC converter shown in FIG. 7 configured as described above is configured to detect a DC current flowing through the detection resistor 109 provided on the output side of the smoothing circuit. Power is always consumed by the detection resistor 109. For this reason, power loss is large,
There is a problem that the conversion efficiency of the DC-DC converter deteriorates.

As a device for solving the above problem, there is a conventional DC-DC converter having a circuit diagram shown in FIG. In the conventional DC-DC converter shown in FIG. 8, the detection resistor 109 provided in the DC-DC converter shown in FIG. 7 is omitted, and the drain (D) and the source (S ) Are connected to current detection signal lines 103a and 103b derived from the control circuit 3. Thus, the first switching circuit 1
The current detection signal lines 103a and 103b are connected to the drain (D) and the source (S) of the control circuit 103, respectively.
Detects the current value when the first switching circuit 101 is in the ON state. At this time, the ON resistance of the first switching circuit 101 causes the first switching circuit 101
Is detected. The control circuit 103
When detecting that a current exceeding a predetermined value flows through the first switching circuit 101, the first switching circuit 1
01 is turned off to prevent an overcurrent from flowing inside the DC-DC converter and on the output side.

[0006]

As described above, in the conventional DC-DC converter shown in FIG. 7, a detection resistor for current detection is provided on the output side after DC conversion, and the current flowing therethrough is detected. Therefore, there is a problem that power is always consumed by the detection resistor. As a result, power consumption was large, and conversion efficiency by the DC-DC converter was poor. On the other hand, the conventional DC-DC converter shown in FIG. 8 is configured to detect the value of the current flowing therethrough using an on-resistance that largely depends on the temperature characteristics of the first switching circuit. Therefore, the current value detected by the DC-DC converter is greatly affected by the ambient temperature, and there is a problem that the detection accuracy is deteriorated. The present invention solves the above problems and provides a DC-DC converter having an overcurrent protection circuit that has high conversion efficiency and that can accurately detect and cut off overcurrent without being affected by ambient temperature. The purpose is to:

[0007]

In order to achieve the above object, a DC-DC converter according to the present invention comprises a first switching means connected to one electrode of a DC input power supply and performing on / off operation; A second switching means for connecting a subsequent stage of the first switching means to the other electrode of the DC input power supply and performing an off / on operation in synchronization with an on / off operation of the first switching means; Control means for controlling the driving of the switching means and the second switching means, a smoothing means connected to the subsequent stage of the second switching means and forming a DC output voltage, the DC input power supply and the first A first detection resistor connected between the first detection resistor and the switching means; and a current value flowing through a series circuit formed by the first detection resistor and the first switching means. And, the current value and a detecting means for outputting to the control means a signal for turning off operation of the first switching-unit time exceeds a predetermined value. The DC-DC converter of the present invention thus configured can provide overcurrent protection without being affected by the ambient temperature without lowering the conversion efficiency.

According to another aspect of the present invention, there is provided a DC-DC converter comprising: first switching means connected to one electrode of a DC input power supply and performing on / off operation; a stage subsequent to the first switching means; A second switching means for connecting to the other electrode of the first switching means and performing an off / on operation in synchronization with an on / off operation of the first switching means; and the first switching means and the second switching means. Control means for controlling the driving of the second switching means, a smoothing means connected to the subsequent stage of the second switching means for forming a DC output voltage, the first switching means and the second
A second detection resistor connected between the first and second switching means, and a current value flowing through a series circuit constituted by the first switching means and the second detection resistor,
Detecting means for outputting a signal for turning off the first switching means to the control means when the current value exceeds a predetermined value. The DC-DC converter of the present invention configured as described above can reduce the conversion efficiency without lowering the conversion efficiency.
It is possible to obtain overcurrent protection that is less affected by the ambient temperature.

According to another aspect of the present invention, there is provided a DC-DC converter comprising: a first switching means connected to one electrode of a DC input power supply for ON / OFF operation; a subsequent stage of the first switching means; A second switching means for connecting to the other electrode of the input power supply and performing an off / on operation in synchronization with the on / off operation of the first switching means; the first switching means and the second switching means; Control means for driving and controlling the means,
A smoothing means connected to the subsequent stage of the switching means for forming a DC output voltage, a first detection resistor connected between the DC input power supply and the first switching means,
A second detection resistor connected between the first switching means and the second switching means; and a first detection resistor, the first switching means, and a second detection resistor. Detecting means for detecting a current value flowing through the series circuit and outputting a signal for turning off the first switching means to the control means when the current value exceeds a predetermined value. The DC-DC converter of the present invention configured as described above can detect an overcurrent with high accuracy and little influence of the ambient temperature without lowering the conversion efficiency.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the DC-DC converter according to the present invention will be described below with reference to the accompanying drawings.

Embodiment 1 Hereinafter, a DC-DC converter according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram showing a DC-DC converter according to the first embodiment. Embodiment 1 As shown in FIG.
In the DC-DC converter described above, a first transistor 1 as first switching means is connected to a positive electrode of a DC input power supply via a detection resistor 7. At the subsequent stage of the first transistor 1, a second transistor 2 as a second switching means for connecting the positive electrode and the negative electrode is provided. Both ends of a series circuit of the detection resistor 7 and the first transistor 1 are connected to a control circuit 3 that controls on / off operations of the first transistor 1 and the second transistor 2 via signal lines 3a and 3b. ing. Control circuit 3
Detects a voltage drop caused by the detection resistor 7 and the first transistor 1 in the ON state of the first transistor 1. The control circuit 3 turns on / off the first transistor 1.
In addition to controlling the off operation, the on / off operation of the second transistor 2 is synchronized with the on / off operation of the first transistor 1.
ON operation is controlled.

In the DC-DC converter of the first embodiment, a commutation diode 6 is connected in parallel with the second transistor 2, and a reactor 4 and a capacitor 5
Is provided. In the DC-DC converter according to the first embodiment configured as described above, the control circuit 3 outputs a predetermined DC voltage by controlling the ON time of the first transistor 1 and the second transistor 2. It is configured as follows. Further, the control circuit 3 detects the current flowing through the detection resistor 7 for current detection and the first transistor 1 in the ON state, and when the detected current exceeds a predetermined current value, the first The transistor 1 is turned off to prevent an overcurrent from flowing inside the DC-DC converter and on the output side. FIG. 2 is a signal waveform diagram in the DC-DC converter according to the first embodiment. FIG. 2A is a voltage waveform of the gate-source voltage Vgs1 of the first transistor 1. FIG. 2B shows the gate-source voltage V of the second transistor 2.
gs2 is a voltage waveform, and (c) is a drain-source voltage Vds2 of the second transistor 2. FIG.
(D) is a waveform of the current (IL) flowing through the reactor 4.

Although the first transistor 1 and the second transistor 2 in the first embodiment have been described by way of examples using general transistors as switching elements,
Similar effects can be obtained by using a switching element such as a field effect transistor (FET), a MOSFET, or a switching element with a built-in resistor. The same effect can be obtained by using a resistor such as a pattern resistor or a wire resistor in addition to a general resistor as the detection resistor 7.

The D of the first embodiment configured as described above
In the C-DC converter, when the on-period of the first transistor 1 is Ton, the off-period is Toff, the input voltage is Vi, and the output voltage is Vo, the input voltage and the output voltage have the following relationship (1). .

Ton / (Ton + Toff) = Vo / Vi-(1)

The output current is Io, and the resistance of the detection resistor 7 is R
Then, the power W consumed by the detection resistor 7 is expressed by the following equation (2) because the first transistor 1 is only in the ON period.

W = R × Io × Io × Vo / Vi (2)

Therefore, the conventional DC-DC converter shown in FIG.
In the case of a DC converter, the detection resistor 1 provided on the output side
Since the current (Io) flowing through the resistor 09 (resistance: R) is detected, the power is always consumed in the detection resistor 109. That is, the power Wa is expressed by the following equation (3).

Wa = R × Io × Io (3)

Therefore, the DC-DC converter of the first embodiment consumes less power Vo / Vi than the conventional DC-DC converter of FIG.

Next, an on-resistance which is a resistance in the on-state of the first transistor 1 will be considered. The variation width of the on-resistance due to the temperature of the first transistor 1 is Δ
Ron, the variation width of the resistance value due to the temperature of the detection resistor 7 is ΔR
Then, the ratio of the fluctuation width between the first transistor 1 and the detection resistor 7 is

ΔRon / Ron ≫ ΔR / R --- (4)

As a result, the ratio of the fluctuation width of the first transistor 1 becomes larger than the ratio of the fluctuation width of the detection resistor 7. First
Assuming that the variation width due to temperature when the transistor 1 and the detection resistor 7 are connected in series is Δ (Ron + R), it is expressed by the following equation (5).

Δ (Ron + R) / (Ron + R) = ΔRon / (Ron + R) + ΔR / (Ron + R) ≒ ΔRon / (Ron + R) --- (5)

Therefore, when the first transistor 1 and the detection resistor 7 are connected in series, the variation due to temperature (ΔRon /
(Ron + R)) is a variation due to temperature when the current is detected only by the ON resistance of the first transistor (ΔRon / Ron / R).
(Ron), (Ron / (Ron + R)) times, which is smaller.

As described above, the DC-DC of the first embodiment
The converter is configured to connect a detection resistor in series to a first transistor, which is a first switching means, and detect a voltage drop across the series circuit. The effect of the temperature characteristic of the series circuit on the detection voltage is sufficiently smaller than the effect of the temperature characteristic when only the first transistor 1 is used to detect the temperature. It is possible to prevent the overcurrent from flowing through the inside of the device and being output to the outside of the device by detecting the voltage drop with little reception and with high accuracy. Further, in the DC-DC converter of the first embodiment, the detection resistor 7
, A current flows only when the first transistor 1 is on, so that the power consumption by the detection resistor 7 is only when the first transistor 1 is on. Therefore, the conventional DC-D shown in FIG.
The loss is smaller than that of the C converter. In particular, as the output voltage is lower than the input voltage, the ON period of the first transistor 1 is shortened, and the power loss is reduced.

In the DC-DC converter of the first embodiment, when detecting that a current exceeding a predetermined value flows, the control circuit 3 turns off the first transistor 1,
It is configured to turn on the second transistor 2.
With this configuration, even if the first transistor 1 that is to be turned off is short-circuited and fails, the second transistor 1
Is in the ON state, the positive electrode and the negative electrode are in a connected state, the overcurrent flows to the negative electrode, and the overcurrent does not flow to the load. Therefore, the DC-
The DC converter can safely protect the load. In particular, by providing a fuse or an electric circuit that cuts off the overcurrent when the overcurrent flows to the input side of the DC-DC converter, even if the first transistor 1 is short-circuited and fails, the second transistor can be connected. Since the flowing overcurrent is cut off, a safe DC-DC converter is obtained.

Second Embodiment A DC-DC converter according to a second embodiment of the present invention will be described below with reference to FIG. FIG. 3 is a circuit diagram showing a DC-DC converter according to the second embodiment. As shown in FIG.
Is a DC-DC converter according to the first embodiment.
The other configuration is the same except for the connection position of the detection resistor in the DC converter. In FIG. 3, components having the same functions and configurations as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 3, the DC-
In the DC converter, a drain terminal (D) of a first transistor 1 serving as first switching means is connected to a positive electrode of a DC input power supply. The detection resistor 8 is connected to the source terminal (S) of the first transistor 1. A second transistor 2, which is a second switching means for connecting the positive electrode and the negative electrode, is provided downstream of the detection resistor 8. Both ends of a series circuit of the first transistor 1 and the detection resistor 8 are connected to the control circuit 3 via signal lines 3a and 3b. The control circuit 3 detects a voltage drop caused by the detection resistor 8 and the first transistor 1 when the first transistor 1 is in the ON state.

The D of the second embodiment configured as described above
In the C-DC converter, the control circuit 3 is configured to output a predetermined DC voltage by controlling the ON time of the first transistor 1 and the second transistor 2. Further, the control circuit 3 includes a detection resistor 8 for detecting a current.
And the current flowing through the first transistor 1 in the on state, and when the detected current exceeds a predetermined current value, the first transistor 1 is turned off, and D
The overcurrent is prevented from flowing inside the C-DC converter and on the output side.

As described above, the DC-DC of the second embodiment
The converter is configured to connect a detection resistor in series to the first transistor and detect a voltage drop across the series circuit, similarly to the DC-DC converter of the first embodiment. Therefore, the DC-DC converter according to the second embodiment detects the voltage drop with high accuracy without being affected by the ambient temperature, and prevents the overcurrent from flowing into and out of the device. Further, in the DC-DC converter of the second embodiment, a current flows through the detection resistor 8 only when the first transistor 1 is in the ON state, so that the power loss due to the detection resistor 8 is small.

The DC-DC converter according to the second embodiment includes:
Since the detection resistor 8 (resistance: R) is connected to the source side of the first transistor 1, the gate-source voltage Vgs ′ of the first transistor 1 is represented by the following equation (6). Here, Vgs indicates a voltage from the gate of the first transistor 1 to the signal line 3b including the detection resistor 8 connected to the source. The current flowing through the first transistor 1 is represented by I.

Vgs' = Vgs-RI-(6)

Therefore, as the current I increases, the gate-source voltage Vgs' of the first transistor 1 decreases. FIG. 4 shows the ON resistance (Ron:
FIG. 6 is a characteristic diagram showing a relationship between a gate-source voltage (Vgs ′: V) and a gate-source voltage (Vgs ′: V). As shown in FIG. 4, the on-resistance (Ron) of the first transistor 1 increases as the gate-source voltage Vgs ′ decreases. For this reason, as the gate-source voltage Vgs' is smaller, the voltage drop due to the on-resistance is larger, and the detection accuracy is higher. As a result, when a current exceeding a predetermined value is detected, the first transistor 1 is reliably turned off, and no overcurrent flows through the device and no overcurrent is output.

When the control circuit 3 detects a current exceeding a predetermined value, if the first transistor 1 is not turned off due to a failure of the control circuit 3 or the like, an overcurrent is supplied to the first transistor 1. Will flow. However, when an overcurrent flows through the first transistor 1, the gate-source voltage Vgs' decreases. FIG. 5 is a characteristic diagram of the first transistor 1 and shows Vgs-Id characteristics. As shown in FIG. 5, when the gate-source voltage Vgs' decreases, no more current flows than a certain level. As a result, according to the second embodiment, DC-DC
Overcurrent does not flow more than a certain amount in the converter,
It becomes a safer DC-DC converter.

Third Embodiment A DC-DC converter according to a third embodiment of the present invention will be described below with reference to FIG. FIG. 6 is a circuit diagram showing a DC-DC converter according to the third embodiment. As shown in FIG.
Is a DC-DC converter according to the first embodiment.
Detection resistor 7 in DC converter and D in Embodiment 2
This is a device in which the detection resistor 8 in the C-DC converter is provided as a detection resistor, and other configurations are the same. In FIG. 6, the same functions as those of the first and second embodiments,
Components having the same configuration are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 6, the DC-
In the DC converter, a drain terminal (D) of a first transistor 1 serving as first switching means is connected to a positive electrode of a DC input power supply via a first detection resistor 70.
The source terminal (S) of the first transistor 1 has a second terminal (S).
Are connected to each other. First detection resistor 70
Corresponds to the detection resistor 7 in the first embodiment, and the second detection resistor 80 corresponds to the detection resistor 8 in the second embodiment. In the subsequent stage of the second detection resistor 80, a second transistor 2, which is a second switching means for connecting the positive electrode and the negative electrode, is provided. The first detection resistor 70, the first
Both ends of a series circuit including the transistor 1 and the second detection resistor 80 are connected to the control circuit 3 via signal lines 3a and 3b. The control circuit 3 includes the first transistor 1
, The voltage drop due to the first detection resistor 70, the first transistor 1, and the second detection resistor 80 is detected.

The D of the third embodiment configured as described above
In the C-DC converter, the control circuit 3 is configured to output a predetermined DC voltage by controlling the ON time of the first transistor 1 and the second transistor 2. Further, the control circuit 3 detects a current flowing in a series circuit including the first detection resistor 70, the first transistor 1 in the ON state, and the second detection resistor 80, and detects the detected current in advance. When the current value exceeds a predetermined value, the first transistor 1 is turned off to prevent an overcurrent from flowing inside the DC-DC converter and on the output side.

The D of the third embodiment configured as described above
The C-DC converter has the same effects as those of the first and second embodiments, and also has the following effects. In the DC-DC converter according to the second embodiment, since the detection resistor is connected to the source side of the first transistor 1, the gate-source voltage Vgs' decreases as the current flows more, and the first transistor 1 Has a large on-resistance. Therefore, the overcurrent is easily detected, and the configuration is highly safe. However, in the configuration of the second embodiment, depending on the set value of the operating current for overcurrent detection, the on-resistance increases due to the decrease in the gate-source voltage Vgs ′, and the overcurrent protection operates before reaching the set value. In some cases. Therefore, by providing the detection resistors 7 and 8 on both the drain side and the source side of the first transistor 1 as the first switching means, the set value of the operating current due to the overcurrent can be adjusted, and The first transistor can be turned off by detecting an overcurrent with high accuracy by a decrease in the source voltage Vgs ′.

[0040]

As apparent from the detailed description of the embodiments, the present invention has the following effects. According to the present invention, it is possible to obtain a DC-DC converter having an overcurrent protection circuit that has high conversion efficiency and that can accurately detect and cut off an overcurrent without being affected by the ambient temperature. In the DC-DC converter according to the present invention, since the detection resistor is connected in series to the first switching means and the voltage drop across the series circuit is detected, the DC-DC converter has high accuracy without being affected by the ambient temperature. , A voltage drop can be detected to prevent an overcurrent from flowing inside the device and being output outside the device.

Further, in the DC-DC converter according to the present invention, a current flows through the detection resistor only when the first switching means is in the ON state and consumes power, so that the device has a small power loss. In particular, the lower the output voltage is compared to the input voltage, the shorter the ON period of the first switching means and the smaller the power loss. Further, in the DC-DC converter according to the present invention, the overcurrent flows, so that the gate-source voltage of the first switching means decreases, and the on-resistance of the first switching means increases. Can be detected.

Further, according to the present invention, even when the control circuit fails, if an overcurrent flows through the first switching means and the gate-source voltage decreases to the threshold voltage, no more overcurrent flows. Therefore, a DC-DC converter having safe overcurrent protection can be obtained. Further, according to the present invention, even if the first switching means is short-circuited and fails, the second switching means is configured to be in the ON state, so that the overcurrent flows through the second switching means. Thus, it is possible to obtain a highly safe DC-DC converter without overcurrent flowing to the load.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a DC-DC converter according to a first embodiment of the present invention.

FIG. 2 is a signal waveform diagram in the DC-DC converter of the first embodiment.

FIG. 3 is a circuit diagram showing a configuration of a DC-DC converter according to a second embodiment of the present invention.

FIG. 4 is a characteristic diagram illustrating a relationship between an on-resistance and a gate-source voltage of a first transistor in Embodiment 2.

FIG. 5 is a characteristic diagram illustrating a relationship between a drain current Id and a gate-source voltage Vgs of a first transistor in Embodiment 2.

FIG. 6 is a circuit diagram showing a configuration of a DC-DC converter according to a third embodiment of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a conventional DC-DC converter.

FIG. 8 is a circuit diagram showing a configuration of another conventional DC-DC converter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first transistor 2 second transistor 3 control circuit 4 reactor 5 capacitor 6 commutation diode 7 detection resistor 8 detection resistor 70 first detection resistor 80 second detection resistor

Claims (5)

[Claims] A first switching means connected to one electrode of a DC input power supply and performing on / off operation; connecting a subsequent stage of the first switching means to the other electrode of the DC input power supply; A second switching unit that performs an on / off operation in synchronization with an on / off operation of the first switching unit; a control unit that drives and controls the first switching unit and the second switching unit; a second switching unit A smoothing means connected to a subsequent stage of the means to form a DC output voltage; a first detection resistor connected between the DC input power supply and the first switching means; Detecting a current value flowing through a series circuit constituted by the first switching means and turning off the first switching means when the current value exceeds a predetermined value; DC-DC converter, characterized by comprising, detecting means for outputting to said control means. No.. A first switching means connected to one electrode of the DC input power supply and performing on / off operation; connecting a subsequent stage of the first switching means to the other electrode of the DC input power supply; A second switching unit that performs an on / off operation in synchronization with an on / off operation of the first switching unit; a control unit that drives and controls the first switching unit and the second switching unit; a second switching unit A smoothing means connected to a subsequent stage of the means and forming a DC output voltage; a second detection resistor connected between the first switching means and the second switching means;
Detecting the value of a current flowing through a series circuit constituted by the switching means and the second detection resistor, and, when the current value exceeds a predetermined value, outputting a signal for turning off the first switching means to the control means. A DC-DC converter, comprising: a detection unit that outputs the data to the DC-DC converter. A first switching means connected to one electrode of the DC input power supply and performing on / off operation; a second stage of the first switching means being connected to the other electrode of the DC input power supply; A second switching unit that performs an on / off operation in synchronization with an on / off operation of the first switching unit; a control unit that drives and controls the first switching unit and the second switching unit; a second switching unit A first detecting resistor connected between the DC input power supply and the first switching means; a first detecting resistor connected between the DC input power supply and the first switching means; A second detection resistor connected between the first and second switching means;
Detecting the value of the current flowing through the series circuit constituted by the detecting resistor, the first switching means, and the second detecting resistor, and turning off the first switching means when the current value exceeds a predetermined value. DC-DC, comprising: a detection unit that outputs a signal to be controlled to the control unit.
converter. 4. When the detecting means detects a current exceeding a predetermined value in the series circuit, the control means turns off the first switching means and turns on the second switching means. The DC-DC converter according to claim 1, 2, or 3, wherein 5. The DC-DC converter according to claim 1, wherein said control means and said detection means are formed integrally.