JPS607372A - Capacitance diagnosing circuit for capacitor - Google Patents

Abstract

PURPOSE:To enable an easy detection of capacitance without separating a capacitor from a power source circuit by detecting a circuit voltage in a charging resistance of a backup power source circuit after the closing of a power source switch to be compared with the reference voltage waveform. CONSTITUTION:A voltage withdrawing circuit 8 is connected to the connection point 9 on the negative pole side of a backup capacitor 3 to extract changes in the terminal voltage of a charging resistance 4. On the other hand, a reference voltage generation circuit 15 is connected to the output terminal O point the same with a voltage detection circuit 14 and the voltage equal to the circuit 14 is applied to be charged into the capacitor 3. A CR constant is set on the circuit 15 in conformity to a charge curve of the capacitor 3 and a diminishing waveform is outputted. Therefore, when output value of the circuit 14 is smaller than the output value of the circuit 15, namely, the capacitance of the capacitor 3 is smaller, a comparator 25 produces an output at the output terminal R and outputs a signal U to an alarm through a buffer circuit 28. Thus, the detetion of catapcitance can be done easily with the capacitor left on the power source circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an air bank device for protecting occupants of high-speed moving objects, particularly automobiles, in the event of a collision.

BACKGROUND ART In this type of air bank device, when a sudden impact is detected, the detonator is energized to ignite the explosive that causes the air bag to deploy, activating the gas generator, and storing the gas pressure. Ij4 configurations for restraining occupants are generally known. By the way, such airbag devices are equipped with a bank amplifier power supply consisting of a capacitor installed in parallel near the device so that the airbag device can operate even if the battery system of the power source fails in the event of a collision. We try to allocate funds when needed. The capacitor used as a backup source must have enough capacity to instantaneously flow enough current to detonate the detonator in the airbag circuit in the event of a car collision, and usually a large-capacity solution is used. capacitor is used.

However, capacitors can be damaged during use, or their capacity can decrease over time, so they must be constantly diagnosed. To diagnose the capacitance of this backup power supply capacitor, it is possible to disconnect the capacitor from the power supply circuit and measure it using a bridge circuit, but this not only makes the work complicated, but also reduces the reliability of the device by disconnecting the circuit. It has disadvantages such as a marked decrease in performance.

DISCLOSURE OF THE INVENTION Accordingly, the present invention was devised in view of the above-mentioned problems, and it is an object of the present invention to provide a capacitance diagnostic circuit for a backup capacitor that can easily detect the capacitance while attached to a device without separating the capacitor from the power supply circuit. It is an object.

The present invention focuses on the fact that the charging and discharging curve of a waste capacitor follows a curve corresponding to the capacitance of the capacitor, and applies this to the fault diagnosis circuit for the capacitor of the bank amplifier power supply circuit. The circuit is configured to detect changes in circuit and pressure in the charging resistor of the backup power supply circuit after the power switch is turned on, and to compare this with a predetermined reference voltage waveform.

That is, the capacitor capacity diagnostic circuit for the backup power supply circuit according to the present invention includes a voltage detection circuit that detects a change in the first position after the power switch is turned on at the connection between the capacitor and the charging resistor, and a voltage detection circuit that detects whether the capacitor of the backup power supply circuit is normal. A CR having a discharge characteristic curve that is a standard for determining whether
A time constant fault circuit is provided, and after a voltage of the same magnitude as the detection point of the voltage detection circuit is applied as a pulse to the time constant circuit for a predetermined sampling period after the power switch is turned on, the voltage of the reference discharge characteristic curve is determined. A reference voltage generating circuit is connected and the magnitudes of the output voltages of both circuits are compared after a predetermined detection time).

Further, in this device, a circuit for preventing erroneous diagnosis is disclosed in case a sufficient detection voltage cannot be obtained, such as when a charge is accumulated in the capacitor to be measured when the power source switch is turned on. According to the capacitance diagnosis circuit for bank amplifier power supply capacitors according to the present invention, failures can be diagnosed simply by turning on the key switch of the power supply without removing the capacitor from the power supply circuit. be.

Best mode for carrying out the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of a capacity diagnostic circuit for a backup capacitor according to the present invention. In the figure, 1 is a direct current battery of an automobile, and 2 is an ignition switch that opens and closes in conjunction with an automobile key switch. 3 is a bank amplifier power supply capacitor consisting of a large capacity aluminum electrolytic capacitor, 4
is a charging resistor for capacitor 3, 5 is a diode for one-way conduction, and backup capacitor 3 is connected to switch 2.
When closed, resistance 4 and diode 5 are connected to Zobanoteri 1.
is charged to the voltage of Although not shown, between the terminals 6 and 6', there is a detonator for igniting an explosive to deploy an airbag installed near the driver's or passenger's seat of a car, and a energizing path for the detonator to detect a collision with a car. A series connection body of collision detection sensors forming the detonation circuit, a monitoring resistor for monitoring the normal operation of these detonation circuits, etc. are connected. Further, 7 is a discharge diode for the capacitor 3, and when the detonator circuit connected between the terminals 6 and 6' is closed in the event of a car collision, the discharge diode 7 is completely passed through and the backup capacitor 3 is charged. The electric charge flows and causes the airbag to deploy. 8 is a voltage extraction circuit connected to the I>RkM point 9 between the negative electrode side of the backup capacitor 3 and the charging/Hi resistor 4, voltage dividing resistor], 0, 11, Zener diode and capacitor for noise removal 12, 13 It consists of etc. 14 and 15 are connected to this voltage extraction circuit 8, and are a voltage detection circuit at the connection point 9 on the negative electrode side of the backup capacitor 3, and a power generation circuit that serves as a reference for this voltage and production circuit. The voltage detection circuit I4 includes an analog switch 17, a reverse blocking diode 18, and a voltage detection resistor 19, which are turned on by the detection pulse of the measurement pulse generation circuit 16 for setting the detection time. 2 has been done. Further, the reference spiral pressure generation circuit 15 includes an analog switch 21 that passes Ni according to the sampling pulse of the sampling pulse generation circuit 20, a reverse blocking diode 22,
It has a predetermined CB time constant and is composed of a capacitor 23 that generates a basic waveform and a compensator 24. 25 is a comparator that compares the output of both circuits 14 and 15; 26 is the voltage number output 1@8 output voltage and set voltage VCC
This is a comparator that compares the set position of the , and is an error prevention circuit for the device during sampling, as will be described later. 27 is 3
In the logical sum circuit of the terminal, when all the outputs of the comparators 25 and 26 and the sampling pulse generation circuit 16 are present, the gate thereof is opened and outputted. Reference numeral 28 denotes a buffer circuit which receives the output pulse of the OR circuit 27 and outputs it to an output terminal 29 to drive a not-shown information system.

Next, the operation of the backup capacitor capacitance (acid receiving detection circuit) with the above configuration will be explained using the waveform diagram shown in Fig. 2.First, the key switch of the car is turned on, and the ignition switch 2 When the power is turned on at time 1-10 as shown in A, power is applied to the measurement pulse generation circuit 16 for setting the detection time and the sampling pulse generation circuit 20, which operate simultaneously, and as shown in FIGS. 2B and C, respectively. The gates of the analog switches 17 and 21 are opened by generating a quantity detection pulse and a sampling pulse having a predetermined detection time tg1 and sampling time tg2 shown in FIG.
Voltage detection circuit 14 and reference voltage generation circuit 1 of the negative electrode side portion of backup capacitor 3 in human power P1 and Q
5, the actual detection potential surface 1WCox located above the reference curve 0ref indicates that the capacitor 3 is good for customer use, and the detection potential curve CNo shown by the lower dotted line shows
indicates a capacitance reduction failure of capacitor 3. That is, the voltage extraction circuit 8 is connected to the jl: connection point 9 on the negative electrode side of the backup capacitor 9, and in this case, the original resistor 40
The voltage change in the voltage of the battery 11 is extracted, and when the ignition switch 2 is turned on, the backup capacitor 9 rapidly decreases in contrast to the voltage of the battery 1 that rises toward the voltage of the battery 1 according to its charging frequency mJ. It's something to do. That is, '40 output points of the voltage extraction circuit 8, therefore '-
The potential curve at the output end P point of the pressure detection circuit 14 has a waveform that gradually decreases with respect to the capacitance of the backup capacitor 9, such as COK and CNG.

On the other hand, the reference water pressure generation circuit 15 is connected to the same output terminal point 0 as the detection circuit 14, and the sampling link time tgz
During this period, the same voltage as that of the detection circuit 14 is applied and the capacitor 23 is charged. The capacitor 23 and the resistor 24 of the circuit 15 have their OR constants set in accordance with the charging curve of the backup capacitor 9, and the output terminal Q gradually decreases as shown by Cref in response to the voltage applied to the output terminal Q point. The waveform is output. Therefore, the comparator 25 outputs an output to its output terminal R when the output value of the detection circuit 14 is smaller than the output value of the reference 1E pressure generation circuit 15, that is, when the capacitance value of the backup capacitor 9 is small. Furthermore, if the backup capacitor 3 is already charged and has a high potential when the ignition switch 2 is turned on, the error prevention circuit 26 prevents the capacitor 3 from being charged by, for example, turning off the engine key and then turning it on again soon. In this case, the voltage extraction circuit 8 cannot obtain a sufficient level for detection. Therefore, when the ignition switch 20 is turned on, the comparator 26 outputs an output to its output terminal S only when a voltage higher than the predetermined set potential VCC is obtained at the output terminal 0 point of the paper pressure extraction circuit 8. The three-terminal OR circuit 27 is
In response to the outputs of these circuits 25 and 26 and the detection output of the pulse generating circuit 16, a signal T is output to the buffer circuit 28 when an insufficient capacity of the backup capacitor 3 is detected in a normal test state. The buffer circuit 28 receives this signal T and outputs a control ti1't1 signal U to an alarm device such as a display device or a buzzer (not shown).

As described above, according to this book, it is possible to detect insufficient capacitor capacity by turning on the key switch without disconnecting the backup capacitor from the power supply circuit, thereby increasing the reliability of airbag systems in automobile collisions. will improve.

[Brief explanation of drawings]

Figure 1 shows a failure diagnosis circuit for detecting a decrease in the capacity of the backup capacitor of the airbag device of the present invention, and Figure 2 shows the
This is a raw diagram of the operating characteristics of the figure. ■...DC'FJL source, 2 switch, 3-capacitor, 4...charging/torque resistor, 8 voltage extraction circuit, 14
tun)j. Detection circuit, 15・Reference voltage generation circuit, 16- +li'
l constant pulse generator, 17-analog switch, 20-sampling pulse generator, 21 analog switch, 2
5... Comparator.

Claims (1)

[Claims] In a backup power supply circuit in which a capacitor and a resistor are connected to a battery power source via a switch, a part of the one-source circuit includes a voltage detection circuit that detects a change in the potential of the resistor after the switch is turned on, and a capacitance of the capacitor. It is equipped with an OR circuit set to a predetermined OR time constant for determining normality, and after a voltage of the same magnitude as the pressure detection circuit is applied for a predetermined sampling period after the switch is turned on, the OR circuit is 1. A capacitor capacity diagnostic circuit, characterized in that it is connected to a reference voltage generation circuit that generates a discharge voltage according to a time constant, and the outputs of these two circuits are compared after a predetermined detection time.