JPH08336233A - Power supply for air bag - Google Patents

Abstract

PURPOSE: To obtain a power supply for air bag composed of parts having relatively low withstand voltage and heat resistance. CONSTITUTION: The battery voltage is stepped down, at a first stabilized power supply section 1, to a predetermined level which is then stabilized, at a second stabilized power supply section 2, at higher accuracy than the first stabilized power supply section 1 before being fed to a CPU 3 or the like while being stepped down. The CPU 3 makes a decision whether the capacitance and internal resistance of a backup capacitor 6, connected in parallel with the first stabilized power supply section 1 on the output side thereof, are acceptable or not. If it is not acceptable, an alarm lamp 15 is lighted and the backup capacitor 6 can be replaced in the early stage of deterioration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly to reducing the withstand voltage and heat resistance characteristics required for electronic parts in a power supply device used in a vehicle safety device represented by an airbag device. The present invention also relates to the one which is intended to maintain the surge resistance characteristic.

[0002]

2. Description of the Related Art As one of typical ones of so-called vehicle safety devices for protecting the body of a vehicle occupant, a bag accommodated in a steering wheel is inflated and deployed when an impact force larger than a predetermined value is detected. Background Art An air bag device that avoids the head and chest of an occupant from colliding with a steering wheel is well known and well known. The airbag device having such a function has a logic circuit that determines the deployment timing of the airbag based on the acceleration obtained by the acceleration sensor by a so-called CPU and generates a necessary control signal. It has a so-called power circuit for supplying a relatively large current to a kind of heater for ignition called a squib in response to a control signal from the.

The power supply system in such an air bag device has a relatively small voltage (for example, about 5V) required for a logic circuit mainly composed of a CPU.
And the relatively large voltage used in the power circuit (for example, about 10 to 20V), the former can be obtained by stepping down and stabilizing the battery voltage installed in the vehicle, and the latter can directly obtain the battery voltage. Or, it is often used after stepping down.

By the way, in a power circuit, a so-called power transistor is often used, and a collector thereof is connected to a so-called battery line connected to a battery to apply a battery voltage. . In such a configuration, a so-called down surge from the battery line often enters and damages the power transistor.Therefore, a Zener diode with a large withstand voltage may be provided to protect the power transistor from such surge. It is necessary to select not only the power transistor itself but also the electronic components around it, which have a high withstand voltage.

[0005]

However, in the air bag device described above, the current consumed in normal time, that is, when the air bag is not deployed, is about several tens mA at the center of the logic circuit. On the other hand, a relatively large current (for example, about 2 to 3 A) is mainly required in the power circuit when the airbag is deployed. However, such a relatively large current is required only for an extremely short time of about 2 msec.

In consideration of the current in such an extremely short time, it is necessary to construct a circuit using a high withstand voltage as described above or, in some cases, a component considering heat dissipation. Extremely low economic efficiency. In addition, since many of such high-voltage and high-heat-resistant parts are large-sized and are not suitable for planar mounting, there arises a problem that the miniaturization and weight reduction required for a vehicle device cannot be satisfied.

In addition to the above-mentioned power circuit, it is actually necessary to select a component in consideration of high breakdown voltage and heat dissipation not only in the power circuit described above but also in a circuit portion that generates a power supply voltage to be supplied to the CPU. That is, assuming that the power supply voltage required for the CPU and the logic circuits around it is, for example, 5 V, this voltage is normally obtained by stepping down and stabilizing the battery voltage by the stabilizing power supply circuit.

For example, even if the battery voltage is 12v, one of the reliability tests is to use such a battery 2
Since it is required that they are connected in series and a voltage is applied and there is no problem in terms of withstand voltage and heat resistance, in this case, the maximum current required in the CPU and logic circuits around it is 30 mA. Then, the stabilized power supply circuit, (24v
-5v) x 0.03A = 0.57W must be able to withstand the power consumption. Therefore, an element having relatively high withstand voltage and large heat dissipation is required, and the same problem as in the power circuit described above occurs.

By the way, in the stabilized power supply circuit used for such an air bag device, a relatively large capacity capacitor called a backup capacitor is connected in parallel on the output side thereof from the viewpoint of so-called fail-safe. Even if the stabilized power supply circuit fails for some reason, the voltage of the backup capacitor enables the circuits such as the CPU connected to the subsequent stage to operate, and the air bag There is no need for the device to fail when it is needed.

The backup capacitor having such an important role may decrease in capacity due to aging, and if it is left unattended, the charging voltage necessary for the operation of the CPU or the like cannot be finally obtained, and the air bag device. There is a risk of causing a serious situation in which the operation of cannot be secured. Therefore, conventionally, there has been proposed a technique capable of measuring the capacity of the backup capacitor and avoiding the above-mentioned inconvenience.

However, it is not only the capacitance of the capacitor that has a great influence on the decrease in the charging voltage, but also the internal resistance that the capacitor normally has is one factor that causes the decrease in the charging voltage. That is, this internal resistance also tends to increase over time, and as the current drawn from the capacitor increases, the voltage drop in the internal resistance increases, resulting in a decrease in the charging voltage that can be output to the outside. However, it is difficult to judge the increase of the internal resistance only by measuring the capacitance, and conventionally, there has been a problem that the backup capacitor has insufficient maintenance management.

The present invention has been made in view of the above circumstances, and provides a power supply device for an air bag device which can be reduced in size and weight. Another object of the present invention is to withstand voltage,
An object of the present invention is to provide a power supply device for an airbag device, which can be configured by parts having relatively small heat resistance.

Another object of the present invention is to provide a power supply device for an air bag device having a function capable of reliably determining the degree of deterioration of a backup capacitor. Another object of the present invention is to provide a power supply device for an airbag device having a function of measuring both the capacity deterioration of the backup capacitor and the fluctuation of the internal resistance.

[0014]

A power supply device for an air bag device according to the present invention comprises a first stabilized power supply device for stabilizing an input voltage from a battery and stepping it down to a first predetermined voltage; The output voltage of the first stabilized power supply means is set to the first
A second step of stepping down to a second predetermined voltage required for a circuit component centered on an integrated circuit which constitutes an airbag control device by stabilizing with a higher accuracy than the voltage stabilizing accuracy of the stabilizing power supply means A stabilized power supply means, and a backup capacitor connected in parallel to the output terminal of the first stabilized power supply means, wherein the first stabilized power supply is provided. Power supply operation control means for controlling the operation of the means, and the first by the power supply operation control means
Measurement means for measuring the charging voltage of the backup capacitor and determining the quality of the backup capacitor based on the measurement result when the stabilized power supply means is deactivated. Is.

In particular, the measurement determining means includes resistance connecting means for connecting a resistor to the backup capacitor as required,
Measuring means for respectively measuring the voltage of the backup capacitor before the resistance is connected to the backup capacitor by the resistance connecting means and the voltage of the backup capacitor at the time when the resistance is connected to the backup capacitor by the resistance connecting means; When the difference between the voltage of the backup capacitor before the resistance is connected to the backup capacitor and the voltage of the backup capacitor at the time when the resistance is connected to the backup capacitor is equal to or more than a predetermined value, the backup capacitor The internal resistance determining means for determining that the internal resistance is defective is preferable.

Further, the measuring means measures the voltage of the backup capacitor after a lapse of a predetermined time from the time when the resistance is connected to the backup capacitor, and at the time when the resistance is connected to the backup capacitor measured by the measuring means. A capacity determining unit that determines that the capacity of the backup capacitor is deteriorated when the difference between the voltage of the backup capacitor and the voltage of the backup capacitor after a predetermined time elapses from the time when the resistor is connected to the backup capacitor is a predetermined value or more. Those including, are preferable.

It is more preferable to provide an alarm means for displaying an alarm when the internal resistance determination means or the capacitance determination means determines that the internal resistance or capacitance is defective.

[0018]

Before the battery voltage is finally set to a relatively low voltage of the IC or the like among the components of the airbag device by the second stabilizing power source means, first, the battery voltage is set by the first stabilizing power source means. The voltage is stabilized with a relatively coarse accuracy, and is stepped down to a desired voltage by the second stabilizing power supply means. Therefore, the electric load on each of the first and second stabilized power supply means is reduced as compared with the case where the voltage of the battery is finally reduced to the required voltage by one stabilized power supply means, which is lower than the conventional one. Then, it becomes possible to configure with smaller parts.

Further, by measuring the voltage of the backup capacitor connected to the output terminal of the first stabilized power supply means, not only the capacity of the backup capacitor is decreased but also the quality of the internal resistance is judged. Therefore, the deterioration of the backup capacitor can be surely known at an early stage.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a power supply device for an airbag device according to the present invention will be described below with reference to FIGS. The members, arrangements, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.

The power supply device for an air bag device (hereinafter referred to as "the present device") in the present embodiment is, in general terms, its first stabilizing power supply unit ("PWS" in FIG. 1).
1 ”) and a second stabilizing power supply unit (described as“ PWS2 ”in FIG. 1) 2 and the second stabilizing power supply unit 2 supplies the power supply voltage Vcc to the CPU 3 and the like. And a CPU that constitutes an airbag device
Backup capacitor 6 as described later by diverting 3
It is configured so that it can measure the capacity and internal resistance and display an alarm (see FIG. 1).

That is, the first stabilized power supply section 1 as the first stabilized power supply means has a diode 4 for reverse connection protection.
It is connected to a battery (not shown) via, and reduces the input voltage from this battery to a voltage suitable for the second stabilized power supply unit 2 and stabilizes it. The first purpose of the first stabilized power supply unit 1 is to reduce the battery voltage to a range suitable for the input voltage of the second stabilized power supply unit 2 before the second stabilized power supply unit 2. Since the final voltage stabilization is performed by the second stabilized power supply section 2, it is sufficient that the accuracy of the voltage stabilization is lower than that of the second stabilized power supply section 2. .

In the case of this embodiment, the battery voltage input to the first stabilized power supply unit 1 is 12v, and the output voltage of the first stabilized power supply unit 1 is set to 10v. Further, the first stabilized power supply unit 1 can output a stabilized voltage, stop the output, and control the operation thereof according to a control signal input from the CPU 3. It is a thing.

A backup capacitor 6 is connected between the positive electrode output terminal of the first stabilized power supply section 1 and the negative electrode line 5, and the first pnp is provided at the positive electrode side output terminal.
The emitter of the transistor 7 is connected to this first pn
The collector of the p-transistor 7 is connected to the negative electrode line 5 via the resistor 8.

Further, the output terminal on the positive electrode side of the first stabilized power supply section 1 is connected to the input side of the second stabilized power supply section 2 and is one of the constituent elements of the airbag device. It is adapted to be connected to one end of a safing switch 9. In addition, the above-mentioned first pnp transistor 7
Is connected to a fifth output port (indicated as "P3" in FIG. 1), which is one of the output ports of the CPU3, and its operation is controlled by the CPU3 (details). Is described later).

The second stabilizing power source section 2 as the second stabilizing power source means receives the output voltage stabilized by the first stabilizing power source section 1 with relatively coarse accuracy as an input, and uses this voltage as a basis. To C
Stabilized voltage required for PU3 etc. (5 in this embodiment)
V) is generated, and the accuracy of stabilization in the second stabilized power supply unit 2 is higher than that in the first stabilized power supply unit 1.

The CPU 3 is a so-called one-chip microcomputer having a built-in ROM, RAM, etc., and is one of the main constituent elements of the airbag apparatus. In this embodiment, the CPU of this apparatus is used. Is diverted as. A detection signal of the acceleration sensor 10 that detects the acceleration of the vehicle is input to the CPU 3.

In order to measure the charging voltage of the backup capacitor 6 described above (details will be described later), the wiring on the input side of the second stabilized power supply section 2 is branched (see FIG. 1), and the CPU
3 is connected to the A / D conversion terminal and the charging voltage of the backup capacitor 6 is A / D provided inside the CPU 3.
The digital signal is converted into a digital signal by a D converter (not shown) and read.

Further, a first output port which is one of the output ports of the CPU 3 (denoted as "P1" in FIG. 1)
Is connected to the base of the second pnp transistor 11. The emitter of the second pnp transistor 11 is connected to the other end of the safing switch 9, and the collector thereof is connected to one end of the heater 12a of the squib 12. Further, the second output port of the CPU 3 (denoted as "P2" in FIG. 1) is connected to the gate of the FET transistor 13, and the source of the FET transistor 13 is at the other end of the heater 12a of the squib 12, The drains are connected to the negative electrode lines 5, respectively.

Furthermore, the fourth output port of the CPU 3 (denoted as "P4" in FIG. 1) is connected to the base of the third npn transistor 14. The emitter of the third npn transistor 14 is connected to the ground, while the collector is the backup capacitor 6
Is connected to one end of an alarm lamp 15 for issuing an alarm for deterioration, and the other end of the alarm lamp 15 is connected to a battery (not shown) via an ignition switch (not shown).

FIG. 2 shows the above-mentioned first stabilized power supply unit 1
A specific example of the above will be described below, and this specific example will be described below with reference to the same figure. In this specific example, basically, the first pnp transistor 20 and the second npn transistor 21 stabilize the stability. And a third npn transistor 22 so that the operation can be controlled.

That is, the first pnp transistor 20
Is connected to the positive terminal of a battery (not shown), while the base is connected to the second npn.
It is connected to the collector of the transistor 21 and this second n
The emitter of the pn transistor 21 is connected to the ground (the negative side of the battery is connected) via the resistor 23.

Further, the second npn transistor 21
Between the emitter of the first pnp transistor 20 and the collector of the first pnp transistor 20.
A diode 24 is connected to the collector side of so that the cathode thereof is the emitter side of the second npn transistor 21.

A Zener diode 25 is provided between the emitter of the first pnp transistor 20 and the ground.
Connect the anode side of the
6 and the Zener diode 25 are connected in series. Furthermore, the connection point between the resistor 26 and the Zener diode 25 is
It is connected to the base of the second npn transistor 21 and to the collector of the third npn transistor 22 for controlling the operation of this circuit.

The emitter of the third npn transistor 22 is connected to the ground, while the control signal from the outside (from the CPU 3 in this embodiment) is input to the base.

In such a configuration, when the control signal having the logical value "0" is input to the base of the third npn transistor 22, the third pnp transistor 20 is operating as the stabilized power supply unit and the first pnp transistor 20 is in operation. An output voltage Vout approximately equal to the Zener voltage of the Zener diode 25 is obtained at the collector of the. When a voltage fluctuation occurs, the current flowing into the resistor 23 via the diode 24 changes according to the voltage fluctuation, and the change is negatively fed back to the Zener diode 25 via the second npn transistor 21. The fluctuation of the output voltage is suppressed.

Now, let us consider the heat radiation balance between the first stabilized power supply section 1 and the second stabilized power supply section 2 in this apparatus. For example, as one of the reliability tests, when the voltage 24v when two batteries are connected in series is applied as an input voltage, the second stabilized power supply unit 2
It is assumed that a maximum current of 30 mA flows into the device. In addition, the output voltage of the first stabilized power supply unit 1 is assumed to be 10v.

Under the above precondition, if the power consumed by the first stabilized power supply unit 1 is P1, then P1 = (24-1
0) × 0.03 = 0.42 W. On the other hand, if the power consumption of the second stabilized power supply unit 2 is P2, then P2 = (10-
5) × 0.03 = 0.15W.

If the second stabilizing power supply unit 2 is not provided, 5v (supplied current is 30mA) supplied to the CPU 3, etc.
In this case, the power consumed by the first stabilized power supply unit is (24−5) × 0.03 = It becomes 0.57W.

That is, by adopting the configuration of the present apparatus, it is possible to appropriately disperse heat between the first stabilized power source section 1 and the second stabilized power source section 2, and as a result, the first stabilized power source section is obtained. The parts used in the part 1 and the second stabilized power supply part 2 can be selected in a smaller size compared to the case where only one stabilized power supply part is used, and further, no heat sink is required. Becomes

Next, the procedure for measuring the capacity of the backup capacitor 6 and the internal resistance by the CPU 3 will be described with reference to the flowchart shown in FIG. First, it is determined whether or not the backup capacitor 6 has been charged (see step 100 in FIG. 4).

The judgment criteria for the completion of charging include, for example, whether or not a predetermined time has elapsed since the operation of this device was started, and the first stabilized power supply unit 1 as described later.
It is preferable to determine whether or not a predetermined time or more has passed since the device was brought into the non-operating state and then returned to the operating state.

When it is determined that the backup capacitor 6 is in the charging completed state (YES in step 100), it is determined whether or not the first stabilized power supply section 1 is in the non-operating state. See step 102 of FIG. 4). That is, from the fifth output port of the CPU 3 to the first
When the control signal for deactivating the stabilized power supply unit 1 is output and it is determined that the first stabilized power supply unit 1 is in the non-operation state (YES in step 102), the backup capacitor 6 The charging voltage will be read (see step 104 in FIG. 4).

The charging voltage of the backup capacitor 6 is
The voltage signal input to the A / D conversion terminal of CPU3 is CP
An A / D converter (not shown) provided inside U3 converts the signal into a digital signal and reads it.

Subsequently, the pseudo load is connected (see FIG. 4).
Step 106). That is, a signal for turning on the first pnp transistor 7 is output from the third output port of the CPU 3, so that a resistor 8 as a pseudo load is provided at both ends of the backup capacitor 6 as the first pnp transistor 7. Will be connected via.

Next, the voltage reading of the backup capacitor 6 immediately after the resistor 8 is connected as described above is performed in the same manner as in step 104 above (see step 108 in FIG. 4), and before the resistor 8 is connected. It is determined whether or not the difference between the current voltage and the current voltage is greater than or equal to a predetermined value (see step 110 in FIG. 4). That is, here, the backup capacitor 6 read in the previous step 104.
Is defined as Vo, the voltage after connecting the resistor 8 is V1, and the difference between the two is ΔV1,
It is determined whether or not ΔV1 = (Vo-V1) is smaller than the predetermined value A.

Since the difference voltage ΔV1 corresponds to the voltage drop due to the internal resistance of the backup capacitor 6, it is determined whether the internal resistance is an appropriate value by checking the magnitude thereof. It will be possible. It should be noted that FIG. 3 shows a characteristic curve showing a voltage change due to a series of processes by the CPU 3 after the charging voltage of the backup capacitor 6 is confirmed to be Vo,
In the figure, time t1 shows the time when the resistor 8 is connected in the above-mentioned step 106, and it is shown that the voltage of the backup capacitor 6 drops from Vo to V1 at this time.

Therefore, when it is determined that ΔV1 is larger than the predetermined value A (NO in step 110), the alarm process is performed (step 1 in FIG. 4).
20). That is, a signal of a logical value "1" that makes the third npn transistor 14 conductive is output from the fourth output port of the CPU 3, and the alarm lamp 15 is turned on when the third npn transistor 14 is conductive. Becomes Therefore, the user can know that the backup capacitor 6 has deteriorated.

On the other hand, when it is judged in step 110 that ΔV1 is smaller than the predetermined value A (in the case of YES),
It is determined whether or not a predetermined time has elapsed since the resistor 8 was connected in the previous step 106 (see step 112 in FIG. 4), and if it is determined that the predetermined time has elapsed, the voltage reading of the backup capacitor 6 is performed again in the previous step. 104,
This is performed in the same manner as 108 (see step 114 in FIG. 4). Here, the time point when a predetermined time has elapsed since the resistor 8 was connected corresponds to time t2 in FIG.

Then, assuming that the voltage read at this time t2 is V2, it is judged whether or not the difference voltage ΔV2 with respect to the voltage V1 read in the previous step 108 is smaller than the predetermined value B ( See step 116 of FIG. 4). That is, the voltage change of the backup capacitor 6 after the connection of the resistor 8 decreases with the passage of time as shown in FIG. 3, but the voltage at the time when a predetermined time Δt2 has passed is the deterioration of the backup capacitor 6. The degree of the decrease becomes larger in accordance with the decrease in the capacity due to.

Therefore, when it is determined that ΔV2 is larger than the predetermined value B (NO in step 116), it is determined that the capacity of the backup capacitor 6 is not appropriate and an alarm process is performed (FIG. 4). Step 1
20). Note that this alarm processing has the same content as described above in the case where it is determined that the internal resistance of the backup capacitor 6 is not appropriate, and therefore description thereof will be omitted here.

On the other hand, when it is judged in step 116 that ΔV2 is smaller than the predetermined value B (in the case of YES), it is determined that the backup capacitor 6 is normal, and C
A control signal for turning off the first pnp transistor 7 is output from the third output port of PU3, and the resistor 8
Is disconnected from the backup capacitor 6, and a series of processing is completed.

After time t2 in FIG. 3, in the portion indicated by the dotted line, the resistor 8 is in the non-connection state, and the voltage of the backup capacitor 6 is instantaneously large as shown by the solid line in FIG. It shows the expected voltage change after the increase.

In the above-described embodiment, the voltage across the backup capacitor 6 is directly taken in by the CPU 3, but the value of the resistor 8 is made relatively large from the viewpoint of preventing over-discharge of the backup capacitor 6. In this case, in order to read the value of ΔV1 more accurately, the voltage of the backup capacitor 6 is set to the CPU via the amplifier circuit.
It is preferable to adopt a configuration in which the data is read into No. 3.

The operation of energizing the squib 12 of the air bag device is not related to the essence of the present device, so a detailed description thereof will be omitted here. Based on the acceleration detected by the sensor 10, the CPU 3 calculates a speed change for a predetermined time, and when the calculated value is determined to be a predetermined value or more, the second pnp transistor 11 and the FET transistor 13 are turned on by the CPU 3. By setting the state, the heater 12a of the squib 12 is energized and the airbag is inflated.

In the above-described embodiment, the CPU 3 and the step 1 shown in FIG. 4 executed by the CPU 3 are executed.
The power supply operation control means is realized by the processing of 02. Also, the first pnp transistor 7 and C
The resistance connecting means is realized by the processing of steps 106 and 118 shown in FIG. 4 executed by the PU 3 and the CPU 3.

Further, the CPU 3 and the steps 104, 108 and 11 shown in FIG.
The measurement means is realized by the processing of 4 above. Further, the internal resistance determining means is realized by the CPU 3 and the processing of step 110 shown in FIG. 4 executed by the CPU 3.

Furthermore, the capacity determining means is realized by the CPU 3 and the processing of step 116 shown in FIG. 4 which is executed by the CPU 3. The CPU 3, the third npn transistor 14, the alarm lamp 15, and the processing of step 120 shown in FIG. 4 executed by the CPU 3 realize an alarm means.

[0059]

As described above, according to the present invention,
When converting the battery voltage into the required voltage, a two-step conversion process is performed to reduce the electrical burden on each stabilized power supply means, while the quality of the internal resistance as well as the capacity of the backup capacitor is reduced. By making it possible to determine even the above, since the electrical characteristics such as withstand voltage and heat resistance of the components constituting each stabilized power supply means can be made lighter than before, As a result, it becomes possible to use a large number of physically small parts that can be mounted on a plane, and it is possible to reduce the size and cost of the device.

Further, since the final stabilizing voltage is obtained by the second stabilizing power source means, it is sufficient that the first stabilizing power source means has a relatively rough electric characteristic.
Circuit design becomes simple. Further, by the configuration using the two stabilized power supply means, a protection function against the dump surge entering from the power supply line connected to the battery is provided by the breakdown voltage of the transistor forming the stabilized power supply means. Therefore, unlike the conventional case, it is not necessary to separately provide a Zener diode for the dump surge countermeasure.

Further, since the backup capacitor is provided on the output side of the first stabilized power supply means, its withstand voltage can be lowered as compared with the conventional one, and therefore a large capacity can be used. Stable backup is possible. Furthermore, since there is no part that performs boosting, there is no risk of noise generation associated with boosting, and therefore it is not necessary to take measures against noise, so the number of parts can be reduced by that amount, and the device can be downsized. .

Furthermore, by adopting a configuration in which the output voltage of the first stabilized power supply means is used as the power supply voltage of the transistor for energizing the squib, compared to the case where the battery voltage is directly applied to the transistor. Therefore, since a transistor with a relatively small withstand voltage can be used,
It is also possible to realize downsizing and cost reduction of the airbag device.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration example in an embodiment of a power supply device for an airbag device according to the present invention.

FIG. 2 is a circuit diagram showing an example of a circuit configuration of a first stabilized power supply unit that constitutes the power supply device for an airbag device shown in FIG.

FIG. 3 is a characteristic diagram showing a voltage change of the backup capacitor due to the operation of measuring the capacity and the internal resistance of the backup capacitor by the power supply device for the airbag apparatus in the example.

FIG. 4 is a flow chart showing a procedure for measuring the capacity and internal resistance of a backup capacitor, which is performed by the power supply device for an airbag device according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st stabilized power supply part 2 ... 2nd stabilized power supply part 3 ... CPU 6 ... Backup capacitor 7 ... 1st pnp transistor 8 ... Resistor 15 ... Alarm lamp

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunihiro Takeuchi 1 Tashino, Tomioka, Gunma 1 Asco Stock Company In-house

Claims (5)

[Claims] 1. A first stabilized power supply means for stabilizing an input voltage from a battery to a first predetermined voltage, and an output voltage of the first stabilized power supply means for the first stabilized power supply means. A second step of stepping down to a second predetermined voltage required for a circuit component centered on an integrated circuit that constitutes an airbag control device by stabilizing the voltage with a higher accuracy than the voltage stabilization accuracy of the stabilized power supply means. A power supply device for an air bag device, comprising: stabilized power supply means; and a backup capacitor connected in parallel to an output terminal of the first stabilized power supply means, the first stabilized power supply means And a power supply operation control means for controlling the operation of the backup power supply operation control means, when the power supply operation control means deactivates the first stabilized power supply means, the charging voltage of the backup capacitor is measured and based on the measurement result. The above Airbag device for a power supply device characterized by comprising by comprising: a determining measuring judging means the quality of click-up capacitor, the. 2. The measurement determining means includes a resistance connecting means for connecting a resistance to the backup capacitor as necessary, a voltage of the backup capacitor before the resistance is connected to the backup capacitor by the resistance connecting means, and the resistance connecting means. The measuring means for measuring the voltage of the backup capacitor at the time when the resistance is connected to the backup capacitor by, respectively, the voltage of the backup capacitor before the resistance is connected to the backup capacitor measured by the measuring means, and the backup capacitor An internal resistance determination unit that determines that the internal resistance of the backup capacitor is defective when the difference from the voltage of the backup capacitor at the time when the resistor is connected is a predetermined value or more. For the airbag device according to claim 1. Power supply. 3. The power supply device for an air bag device according to claim 2, further comprising alarm means for displaying an alarm when the internal resistance determination means determines that the internal resistance is defective. 4. The measuring means measures the voltage of the backup capacitor after a lapse of a predetermined time from the time when the resistance is connected to the backup capacitor, while measuring the voltage at the time when the resistance is connected to the backup capacitor measured by the measuring means. A capacity determining unit that determines that the capacity of the backup capacitor is deteriorated when the difference between the voltage of the backup capacitor and the voltage of the backup capacitor after a predetermined time elapses from the time when the resistor is connected to the backup capacitor is a predetermined value or more. The power supply device for an air bag device according to claim 2 or 3, further comprising: 5. The power supply device for an air bag device according to claim 4, further comprising alarm means for displaying an alarm when the capacity determination means determines that the capacity has deteriorated.