JP2004015984A - Switching power supply with destruction prevention function and air bag device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a switching element from being damaged by an overcurrent even when a DC/DC converter control circuit falls in an operation fault under the influence of a static electricity or a noise. <P>SOLUTION: When a transistor Tr2 of a destruction preventing circuit 7 detects that a continuous overcurrent of the destruction preventing circuit 7 flows to a switching element Q1 according to the operation fault of the DC/DC converter control circuit 5, an extrapolation switching signal is generated by a transistor Tr2 of the destruction preventing circuit 7, and the switching element Q1 is turned ON or OFF. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply device with a destruction prevention function and an airbag device using the switching power supply device.
[0002]
[Prior art]
FIG. 4 is a block diagram showing the configuration of a conventional step-up switching power supply device. In the drawing, reference numeral 21 denotes a DC power supply, 22 denotes a current detection unit, 23 denotes a switch control unit, 24 denotes a voltage comparison unit, and 25 denotes a current detection unit. A DC / DC converter control circuit of an LSI (Large Scale Integrated Circuit) including a unit 22, a switch control unit 23, and a voltage comparison unit 24, 26 is a load, Q21 is a switching element composed of FET, R21 and R22 are resistors, and L21 is A coil, V1 is an input voltage from the DC power supply 21, and V2 is an output voltage supplied to the voltage comparison unit 24 and the load 26.
[0003]
Next, the operation will be described. When the switching element Q21 is on, energy is stored in the coil L21, and when the switching element Q21 is off, the stored energy is released and superimposed on the input voltage V1, thereby increasing the output voltage V2 which is boosted. And the load 26. The voltage comparison unit 24 compares the output voltage V2 (actually, a voltage obtained by dividing V2) with a reference voltage and provides a control signal to the switch control unit 23. The switch control unit 23 inputs a switching signal to the gate of the switching element Q21 via the resistor R22 according to the control signal. The switching element Q21 repeatedly turns on and off according to the switching signal.
[0004]
Now, when a trouble occurs in the load 26 and an overcurrent flows through the coil L21, a voltage drop occurs in the resistor R21 connected in series to the coil L21. As a result, the current detector 22 detects an overcurrent based on the voltage drop, and supplies a detection signal to the switch controller 23. The switch control unit 23 inputs a low-level signal to the gate of the switching element Q21 via the resistor R22 according to the detection signal. The switching element Q21 is turned off by this low level signal. Therefore, the output voltage V2 is not boosted, and an overload applied to the DC power supply 21 can be prevented.
[0005]
[Problems to be solved by the invention]
Since the conventional step-up switching power supply device is configured as described above, if a malfunction occurs in the DC / DC converter control circuit 25 and the gate of the switching element Q21 is fixed at a high level, an excessive There is a problem that the switching element Q21 is destroyed by the current. Since the DC / DC converter control circuit 25 is constituted by an LSI such as a CMOS, it has the advantage of high integration and low power consumption, but has the disadvantage of being easily affected by static electricity and noise. Therefore, naturally, measures against static electricity and noise are taken in the design, and it can be said that the probability of damage to the LSI itself is extremely low.
[0006]
However, there is a possibility that the operation may temporarily fall due to the influence of static electricity or noise. Such accidental phenomena are often not found during the IC development (breadboard) stage or the test stage after IC integration, and occur rarely after being incorporated into a product. For this reason, even if the DC / DC converter control circuit 25 temporarily malfunctions and the current detection unit 22 does not function, and then the normal operation is restored, during the malfunction, the overcurrent causes the malfunction. The switching element Q21 may be destroyed.
[0007]
Further, when the above-described conventional step-up type switching power supply device is used for an airbag device that deploys an airbag at the time of a vehicle collision, even if the operation failure of the DC / DC converter control circuit 25 is temporary and accidental. However, there is a problem that it can be extremely dangerous from the viewpoint of human life protection.
[0008]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and even when a DC / DC converter control circuit malfunctions under the influence of static electricity or noise, a switching element is destroyed by an overcurrent. It is an object of the present invention to obtain a switching power supply device that prevents the occurrence of the switching power.
Further, the present invention avoids a dangerous state in which an airbag does not deploy even when a DC / DC converter control circuit of a switching power supply device incorporated therein malfunctions due to the influence of static electricity or noise. It is an object of the present invention to obtain an airbag device that can be used.
[0009]
[Means for Solving the Problems]
A switching power supply with a breakdown prevention function according to the present invention includes a switching element that boosts an input first DC voltage in cooperation with a predetermined inductance element in response to a switching signal and outputs a second DC voltage. A signal generating means for generating a switching signal and applying the signal to the switching element; a current detecting means for detecting that a continuous overcurrent has flowed through the switching element due to a malfunction of the signal generating means; When an overcurrent is detected, a complementary switching signal is generated by generating a complementary switching signal to turn on / off the switching element.
[0010]
The supplementary signal generating means of the switching power supply with destruction prevention function according to the present invention is configured to include a time constant circuit for setting a duty ratio between an on period and an off period of the switching element.
[0011]
The time constant circuit of the switching power supply with the destruction prevention function according to the present invention sets the duty ratio substantially equal to the duty ratio between the ON period and the OFF period of the switching element determined by the switching signal generated by the signal generation unit. It is what was constituted.
[0012]
The current detecting means and the complementary signal generating means of the switching power supply device with the destruction prevention function according to the present invention are constituted by discrete components including two transistors, two resistors, and one capacitor.
[0013]
The current detection means and the supplementary signal generation means of the switching power supply with destruction prevention function according to the present invention are configured so as to stop operating when the signal generation means is operating normally.
[0014]
An airbag device according to the present invention includes a switching element that boosts an input first DC voltage in response to a switching signal in cooperation with a predetermined inductance element and outputs a second DC voltage; A signal generation unit that generates and supplies the switching element with the continuous overcurrent; a current detection unit that detects that a continuous overcurrent flows through the switching element due to a malfunction in the signal generation unit; When detected, a complementary signal generating means for generating a complementary switching signal to turn on / off the switching element, an acceleration switch for switching from off to on when receiving a vehicle impact, and an acceleration switch for on The airbag is instantaneously deployed by applying the second DC voltage output from the switching element at times. It is obtained by a configuration in which a fire element.
[0015]
The current detecting means and the complementary signal generating means of the airbag device according to the present invention are constituted only by hardware.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a configuration of an embodiment of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a step-up switching power supply device according to a first embodiment. In the drawing, reference numeral 1 denotes a DC power supply, 2 denotes a current detection unit, 3 denotes a switch control unit (signal generation unit), Is a voltage comparison unit, 5 is a DC / DC converter control circuit of an LSI including a current detection unit 2, a switch control unit 3, and a voltage comparison unit 4, 6 is a load, 7 is a destruction prevention circuit, and Q1 is a switching element composed of an FET. , Tr1 are transistors (current detecting means), Tr2 is a transistor (complementary signal generating means), R1, R2, R3, and R4 are resistors, C1 is a capacitor, L1 is a coil (inductance element), and V1 is an input from the DC power supply 1. The voltage (first DC voltage) and V2 are output voltages (second DC voltages) supplied to the voltage comparison unit 4 and the load 6.
[0017]
Next, the operation will be described. When the switching element Q1 is on, the energy is stored in the coil L1, and when the switching element Q1 is off, the stored energy is released and superimposed on the input voltage V1. And the load 6. The voltage comparison unit 4 compares the output voltage V2 (actually, a voltage obtained by dividing V2) with a reference voltage and provides a control signal to the switch control unit 3. The switch control unit 3 inputs a switching signal to the gate of the switching element Q1 via the resistor R4 according to the control signal. The switching element Q1 repeats ON / OFF according to the switching signal.
[0018]
When an overcurrent flows due to an overload, the current detection unit 2 detects a voltage drop of the resistor R3 and provides a detection signal to the switch control unit 3. The switch control unit 3 inputs a low-level signal to the gate of the switching element Q1 via the resistor R4 according to the detection signal. The switching element Q1 is turned off in response to the low level signal. As a result, the output voltage V2 is not boosted, preventing overload on the DC power supply 1.
[0019]
FIG. 2 is a timing chart showing waveforms of voltages of respective parts in the switching power supply device of FIG. When the DC / DC converter control circuit 5 of the switching power supply device is operating normally, the voltage at the point a in FIG. 1 which is the output of the switch control unit 3 is, as shown in FIG. The switching signal is turned on / off between a high level (H) and a low level (L), that is, GND. In this state, as shown in FIG. 2B, the voltage at point b in FIG. 1 slightly decreases when the voltage at point a is at a high level, but maintains a value substantially equal to voltage V1. That is, the voltage drop of the resistor R3 maintains a value smaller than _VBE1 of the transistor Tr1.
[0020]
Therefore, the transistor Tr1 is in an off state as illustrated in FIG. As a result, the voltage at the point d in FIG. 1, which is the connection point between the collector of the transistor Tr1 and the resistor R1, is at a low level as shown in FIG. Further, the transistor Tr2 is in an off state as illustrated in FIG. Therefore, as shown in FIG. 2F, the voltage at the point f in FIG. 1, which is the gate of the switching element Q1, turns on and off between the high level and the low level in accordance with the voltage at the point b in FIG. The switching signal is turned off.
[0021]
When the operation of the DC / DC converter control circuit 5 becomes abnormal due to the influence of static electricity or noise and the point a in FIG. 1 which is the output of the switch control unit 3 is fixed to a high level, the switching element Q1 Overcurrent flows in As a result, the voltage at point b in FIG. 1 gradually decreases. That is, the voltage drop of the resistor R3 gradually increases. Then, when the voltage at the point b is lower than V1− _VBE1 , the transistor Tr1 changes from off to on. As a result, the voltage at point d in FIG. 1 changes from a low level to a high level, as shown in FIG. Further, since the base of the transistor Tr2 goes high through the resistor R2, the transistor Tr2 changes from off to on as shown in FIG. As a result, the voltage at the point f in FIG. 1, which is the gate of the switching element Q1, changes from the high level to the low level, as shown in FIG. Therefore, the switching element Q1 changes from on to off.
[0022]
Therefore, the current of the resistor R3 decreases, and the voltage drop decreases. When the voltage at the point b becomes higher than V1− _VBE1 , the transistor Tr1 changes from on to off. That is, as shown in FIG. 2C, the transistor Tr1 is turned on only for a very short period. However, the capacitor C1 is gradually charged according to the parallel resistance of the resistors R1 and R2 and the time constant determined by the capacitor C1. Therefore, the voltage at the point d in FIG. 1 does not decrease sharply, but gradually decreases in an exponential function curve according to the time constant as shown in FIG. 2 (D). Therefore, even after the transistor Tr1 is turned off, the transistor Tr2 remains on.
[0023]
Then, when the voltage at the point d becomes lower than V _BE2 of the transistor Tr2, the transistor Tr2 changes from on to off as shown in FIG. That is, the duty ratio between the ON period T1 and the OFF period T2 of the transistor Tr2 is determined by the parallel resistance of the resistors R1 and R2 and the time constant of the capacitance of the capacitor C1. In the period T2 in which the transistor Tr2 is off, the voltage at the point f in FIG. 1 changes to a high level as shown in FIG. 2F, so that the switching element Q1 is turned off during the period T2 in which the transistor Tr2 is off. Turn on.
[0024]
When the operation of the DC / DC converter control circuit 5 has returned to normal due to the elimination of static electricity and noise, a normal switching signal is supplied from the switch control unit 3 to the gate of the switching element Q1. As shown in (A) to (F), the waveforms of the voltages at the respective parts also return to the original state.
[0025]
As described above, according to the first embodiment, the transistor Tr1 of the destruction prevention circuit 7 detects that a continuous overcurrent flows through the switching element Q1 due to the malfunction of the DC / DC converter control circuit 5. In this case, the complementary switching signal is generated by the transistor Tr2 of the destruction prevention circuit 7, and the switching element Q1 is turned on and off. Therefore, the DC / DC converter control circuit 5 is affected by static electricity and noise and malfunctions. In this case, the switching element Q1 can be prevented from being broken by an overcurrent.
[0026]
Further, according to the first embodiment, since the time constant circuit including the capacitor C1 and the resistors R1 and R2 for setting the duty ratio of the ON period and the OFF period of the switching element Q1 is included, the condition that the switching element Q1 is not destroyed is included. Can be easily set.
[0027]
Further, according to the first embodiment, the destruction prevention circuit 7 is constituted by discrete components including two transistors Tr1 and Tr2, two resistors R1 and R2, and one capacitor C1. In addition to being extremely inexpensive, even if the DC / DC converter control circuit 5 malfunctions due to the influence of static electricity or noise, it is not affected by the malfunction, so that the switching element Q1 is reliably prevented from being destroyed. The effect that can be obtained is obtained.
[0028]
Furthermore, according to the first embodiment, the destruction prevention circuit 7 stops operating when the DC / DC converter control circuit 5 is operating normally, and is therefore configured by discrete components in a normal state. The effect that power is not consumed by the breakdown prevention circuit 7 is obtained.
[0029]
As a modification of the first embodiment, the duty ratio substantially equal to the duty ratio of the ON period and the OFF period of the switching element Q1 determined by the switching signal generated by the switch control unit 3 of the DC / DC converter control circuit 5. Can be set by a time constant circuit including the capacitor C1 and the resistors R1 and R2. In this case, even if the DC / DC converter control circuit 5 malfunctions due to the influence of static electricity or noise, the function of the DC / DC converter control circuit 5 is substituted by the destruction prevention circuit 7 so that the load is reduced. 6 can be maintained at an appropriate level.
[0030]
Embodiment 2 FIG.
FIG. 3 is a block diagram illustrating a configuration of an airbag device using the switching power supply device according to the first embodiment. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Other components include a squib (fire element) 8 for deploying an airbag (not shown) when current flows, a microcomputer 9 for controlling the airbag device, 10, 11 a squib driver for driving the squib, 12 is a regulator of 5 volts, 13 is a semiconductor integrated circuit composed of an LSI including the squib drivers 10, 11, the regulator 12, and the DC / DC converter control circuit 5, and SW1 is a DC power supply 1 (in this case, a battery power supply). -Power switch to be turned off, SW2 is an acceleration switch that is turned on in the event of a vehicle collision, C2 is a backup capacitor, Tr3 is a voltage stabilizing transistor, D1 and D2 are diodes, and V3 is a stabilization of 5 volts output from the transistor Tr3. Voltage.
[0031]
Next, the operation will be described. However, the operation of the switching power supply device is almost the same as the operation in the first embodiment, and the description thereof will be omitted. The input voltage V1 is applied to the acceleration switch SW2 via the diode D1, and the output voltage V2 boosted by the switching element Q1 and stored in the backup capacitor C2 is applied via the diode D2. In the normal state, the output voltage V2 is higher than the input voltage V1, so the output voltage V2 is applied to the acceleration switch SW2.
[0032]
The squib driver 10 connects the acceleration switch SW2 to one terminal of the squib 8 according to a control signal from the microcomputer 9. The squib driver 11 connects the other terminal of the squib 8 to GND according to a control signal from the microcomputer 9. The transistor Tr3 converts the output voltage V2 of 15 volts to 20 volts into a stabilized voltage V3 of 5 volts under the control of the regulator 12, and supplies the stabilized voltage V3 to the microcomputer 9.
[0033]
Now, it is assumed that the squib drivers 10 and 11 are turned on by a control signal from the microcomputer 9. In this case, when the acceleration switch SW2 is turned on due to a collision of the vehicle, the output voltage V2 is supplied to one terminal of the squib 8 via the squib driver 10 in the on state, and the squib driver 11 in the on state. One terminal of the squib 8 is connected to GND. As a result, a current flows through the squib 8 to deploy the airbag.
[0034]
If the operation of the DC / DC converter control circuit 5 becomes abnormal due to the influence of static electricity or noise and the voltage applied from the switch control unit 3 to the gate of the switching element Q1 is fixed at a high level, switching due to overcurrent will occur. In order to prevent the destruction of the element Q1, the destruction prevention circuit 7 composed of discrete components operates as in the first embodiment.
[0035]
As described above, according to the second embodiment, when a continuous overcurrent flows through the switching element Q1 due to a malfunction of the DC / DC converter control circuit 5 incorporated in the airbag device, destruction is prevented. Since the switching element Q1 is turned on / off by generating a complementary switching signal by the circuit 7, even if the DC / DC converter control circuit 5 malfunctions due to the influence of static electricity or noise, the switching element is caused by overcurrent. This has the effect of preventing Q1 from being destroyed and avoiding a dangerous state in which the airbag does not deploy. Further, since the destruction prevention circuit 7 is constituted only by hardware, an effect is obtained that conventional software resources of the microcomputer 9 for controlling the airbag device can be used as they are.
[0036]
【The invention's effect】
As described above, according to the present invention, the switching power supply device with the destruction prevention function boosts the input first DC voltage in cooperation with the predetermined inductance element in accordance with the switching signal, thereby increasing the second DC voltage. A switching element that outputs a voltage, a signal generation unit that generates a switching signal and provides the switching element with the switching element, and a current detection unit that detects that a continuous overcurrent flows through the switching element due to a malfunction of the signal generation unit. When a continuous overcurrent is detected by the current detecting means, a complementary switching signal is generated by turning on / off the switching element by generating a complementary switching signal. Even if the signal generating means malfunctions, the switching element can be prevented from being destroyed by the overcurrent. That.
[0037]
According to the present invention, the supplementary signal generating means of the switching power supply device with the destruction prevention function is configured to include the time constant circuit for setting the duty ratio between the ON period and the OFF period of the switching element, so that the switching element is not destroyed. There is an effect that conditions can be easily set.
[0038]
According to the present invention, the time constant circuit of the switching power supply device with the destruction prevention function is set to a duty ratio substantially equal to the duty ratio of the ON period and the OFF period of the switching element determined by the switching signal generated by the signal generation unit. Even if the signal generation means malfunctions due to the influence of static electricity or noise, the function of the signal generation means is substituted by the complementary signal generation means, so that the output voltage to the load can be properly adjusted. The effect is that it can be maintained.
[0039]
According to the present invention, the current detecting means and the complementary signal generating means of the switching power supply device with the destruction prevention function are constituted by discrete components including two transistors, two resistors, and one capacitor. In addition to the above, even when the signal generating means malfunctions due to the influence of static electricity or noise, the switching element can be reliably prevented from being destroyed.
[0040]
According to the present invention, the current detection means and the supplementary signal generation means of the switching power supply with the destruction prevention function are configured so as to stop operating when the signal generation means is operating normally. In the state, there is an effect that power is not consumed by the current detecting means and the complementary signal generating means constituted by discrete components.
[0041]
According to the present invention, the airbag device is provided with a switching element that boosts an input first DC voltage in cooperation with a predetermined inductance element in response to a switching signal and outputs a second DC voltage, A signal generating means for generating a signal and applying the signal to the switching element; a current detecting means for detecting that a continuous overcurrent flows through the switching element due to a malfunction of the signal generating means; and a continuous overcurrent by the current detecting means. When a signal is detected, a complementary signal generating means for generating a complementary switching signal to turn on / off the switching element, an acceleration switch for switching from off to on when receiving a vehicle impact, and an acceleration switch for on A firing element that instantaneously deploys the airbag by applying a second DC voltage output from the switching element; With this configuration, even if the signal generation unit malfunctions due to the influence of static electricity or noise, the switching element is prevented from being destroyed by overcurrent, and there is a danger that the airbag will not deploy. There is an effect that a complicated state can be avoided.
[0042]
According to the present invention, since the current detecting means and the supplementary signal generating means of the airbag device are constituted only by hardware, there is an effect that the conventional software resources of the microcomputer for controlling the airbag device can be used as they are.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a switching power supply device with a destruction prevention function according to Embodiment 1 of the present invention.
FIG. 2 is a timing chart showing waveforms of voltages of respective parts in the switching power supply device of FIG.
FIG. 3 is a block diagram showing a configuration of an airbag device according to Embodiment 2 of the present invention.
FIG. 4 is a block diagram illustrating a configuration of a conventional switching power supply device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 DC power supply, 2 current detection part, 3 switch control part (signal generation means), 4 voltage comparison part, 5 DC / DC converter control circuit, 6 load, 7 destruction prevention circuit, 8 squib (fire element), 9 microcomputer , 10, 11 squib driver, 12 regulator, 13 semiconductor integrated circuit, 21 DC power supply, 22 current detection unit, 23 switch control unit, 24 voltage comparison unit, 25 DC / DC converter control circuit, 26 load, C1 capacitor, C2 backup Capacitor, D1, D2 diode, L1 coil (inductance element), L21 coil, Q1 switching element, Q21 switching element, R1, R2, R3, R4 resistance, R21, R22 resistance, SW1 power switch, SW2 acceleration switch, Tr1 transistor ( Current detection means), Tr2 transistor Complementary signal generating means), a transistor for Tr3 voltage stabilization, V1 input voltage (first DC voltage) V2 output voltage (second DC voltage) V3 stabilized voltage.

Claims (7)

A switching element that boosts an input first DC voltage in cooperation with a predetermined inductance element in response to a switching signal and outputs a second DC voltage;
Signal generating means for generating the switching signal and providing the switching signal to the switching element;
Current detection means for detecting that a continuous overcurrent has flowed through the switching element due to a malfunction of the signal generation means,
A switching power supply device with a destruction prevention function, comprising: a complementary signal generating means for generating a complementary switching signal to turn on / off the switching element when a continuous overcurrent is detected by the current detecting means. 2. The switching power supply device with a destruction prevention function according to claim 1, wherein the complementary signal generating means includes a time constant circuit for setting a duty ratio between an ON period and an OFF period of the switching element. 3. The destruction prevention function according to claim 2, wherein the time constant circuit sets a duty ratio substantially equal to a duty ratio between an ON period and an OFF period of the switching element determined by the switching signal generated by the signal generation unit. With switching power supply. 4. The current detecting means and the complementary signal generating means are constituted by discrete components including two transistors, two resistors, and one capacitor. The switching power supply device with a destruction prevention function according to claim 1. The destruction according to any one of claims 1 to 4, wherein the current detection means and the complementary signal generation means stop operating when the signal generation means is operating normally. Switching power supply with prevention function. A switching element that boosts an input first DC voltage in cooperation with a predetermined inductance element in response to a switching signal and outputs a second DC voltage;
Signal generating means for generating the switching signal and providing the switching signal to the switching element;
Current detection means for detecting that a continuous overcurrent has flowed through the switching element due to an operation failure in the signal generation means,
When a continuous overcurrent is detected by the current detecting means, a complementary signal generating means for generating a complementary switching signal to turn on / off the switching element,
An acceleration switch that switches from off to on when receiving a vehicle impact,
An airbag device comprising: a fire element that instantaneously deploys an airbag by applying the second DC voltage output from the switching element when the acceleration switch is turned on. 7. The airbag device according to claim 6, wherein the current detecting means and the complementary signal generating means are constituted only by hardware.

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