JPH10282169A - Circuit for diagnosing capacitance of capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diagnose open circuit state of a charge/discharge circuit by comparing the capacitance of a backup capacitor with a predetermined value. SOLUTION: In the case of an open circuit failure of a third diode 25 for blocking reverse flow, an ignition switch 24 is turned on to begin charging of a backup capacitor 26 through a second diode 23 for blocking reverse flow but the backup capacitor 26 is not charged by a DC/DC converter 21. Consequently, the voltage at point A exceeds a reference voltage V2 but it is saturated with a voltage divided by resistors R1 , R3 , R4 and a reference voltage V1 is not exceeded. Subsequently, a switching transistor Tr1 is turned on to start discharge and the voltage is dropped slightly but a constant voltage is kept at the point A because the charging operation is sustained from a battery 20 through the second diode 23 for blocking reverse flow. Since the voltage does not drop below the reference voltage V1 , a timer is not actuated and the open circuit failure of the third diode 25 for blocking reverse flow is notified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacity diagnostic circuit for a capacitor such as a backup capacitor used in an occupant protection device such as an airbag for protecting an occupant of a vehicle from a collision accident.

[0002]

2. Description of the Related Art An example of a circuit for diagnosing the capacity of a capacitor of this type will be described with reference to Japanese Utility Model Publication No. 6-8935 shown in FIG. In the figure, reference numeral 20 denotes a vehicle-mounted battery, 21 denotes a DC / DC converter for boosting and outputting the output voltage of the battery 20, and its input terminals are a first backflow prevention diode 22 and an ignition switch 24.
Are connected to the battery 20 in series. 23 is a second backflow prevention diode, the anode of which is connected to the battery 20 via the ignition switch 24;
The cathode is connected to the output terminal of the DC / DC converter 21 via a third backflow prevention diode 25. Reference numeral 26 denotes a backup capacitor which is connected to a connection point X between the second and third backflow prevention diodes 23 and 25 via an inrush current prevention resistor R1.

[0003] A discharge diode 27 has its cathode connected to the output terminal of the DC / DC converter 21 via the third backflow prevention diode 25. Thereby, the backup capacitor 26 is charged by the output voltage V0 of the DC / DC converter 21. or,
This output voltage V0 is supplied to a processing circuit (including a signal processing circuit such as a diagnostic circuit) 28 as a power supply monitor input. One end of the backup capacitor 26 is connected to the collector of the switching transistor Tr1 via a resistor R2.
More control signals are supplied.

The terminal voltage of the backup capacitor 26 is divided by resistors R3 and R4, and the voltage divided at point A in FIG. 4 is applied to one input terminal of each of comparators 29 and 30. The output voltage V0 is equal to the resistances R5, R6, R7.
One voltage V1 obtained by the voltage division is applied to the other input terminal of the comparator 29 as a reference voltage, and the other voltage V2 (V2 <V1) is applied to the other input terminal of the comparator 30 as a reference voltage. Have been. Comparator 3
The output B of 0 and the output C of the comparator 29 are supplied to the processing circuit 28 and used for checking the capacitance C1 of the backup capacitor 26.

Here, the signal processing of the processing circuit 28 is described with reference to FIG.
This will be briefly described based on the flowchart shown in FIG. That is, when power is supplied, the processing circuit 28 turns on the switching transistor Tr1 for a certain period of time, and discharges the charge stored in the backup capacitor 26 via the resistor R2 (step 100). At a timing when the voltage at the point A falls below the reference voltage V1, the timer is activated to start the timekeeping operation (step 110). Next, A
The timing operation of the timer is stopped at a timing when the voltage at the point further decreases and falls below the reference voltage V2 (step 120), and it is necessary for the charging voltage of the backup capacitor 26 to decrease by a constant voltage (V1-V2). The time is measured, and the backup capacitor 2 is measured based on the measured time.
6 is measured (step 130), and if the measured value is smaller than the specified value, a warning signal is output indicating that the capacity is insufficient.

Next, a more detailed description will be given with reference to FIG. When the ignition switch 24 is turned on, DC
An output voltage V0 is obtained from the / DC converter 21, and with this output voltage V0, the backup capacitor 26 is charged with a predetermined time constant through the resistor R1. As a result, the voltage waveform at the point A proportional to the terminal voltage of the backup capacitor 26 becomes a waveform as shown in FIG. Reference voltages V1 and V2 are applied to the other input terminals of the comparators 29 and 30, respectively. As a result, first, when the output waveform at the point A reaches V2, the output waveform point B of the comparator 30 goes high at the point a.
Next, when the output waveform at point A reaches V1 at point b, the output waveform point C of the comparator 29 goes high.

As a result, a control signal is sent from the processing circuit 28 to the base of the transistor Tr1, and the transistor Tr1 is turned on. Therefore, the electric charge of the backup capacitor 26 is discharged through the resistor R2 and the transistor Tr1, and the output waveform at the point A drops. And FIG.
When the voltage at point C reaches V1, the output waveform at point C is inverted to low level, and when the voltage reaches V2 at point d, the output waveform at point B also inverts to low level. The processing circuit 28 measures the discharge time t from the point C to the point d, performs an operation based on the t, and calculates the capacitance C1 of the backup capacitor 26.

[0008] Further, V2 is selected to be larger than the voltage required for deploying the airbag. If the capacitance C1 obtained by this calculation falls within the predetermined allowable range, the processing circuit 28 turns off the transistor Tr1 and ends the check. Thereafter, the backup capacitor 26 is charged again and prepares for the deployment of the airbag. If the capacity C1 does not fall within the predetermined range due to the deterioration of the backup capacitor 26, an alarm is issued.

[0009]

However, in the capacity diagnosis of such a capacitor, only a failure diagnosis is performed on the point that the capacitance becomes smaller than a specified value due to deterioration of the backup capacitor due to aging. I have.

The present invention has been made in view of such a problem, and an object of the present invention is to diagnose a disconnection state of a charge / discharge circuit of a backup capacitor by using the capacity diagnosis of the backup capacitor.

[0011]

The capacity diagnosis of a capacitor according to the present invention includes a backup capacitor, a battery, a charging circuit for charging the backup capacitor in parallel with a boosted voltage of the battery, and charging the backup capacitor. Discharge circuit for forcibly discharging the
The operation of the discharge circuit is controlled, and the magnitude of the capacitance of the backup capacitor is calculated based on the time constant of the charge / discharge waveform of the backup capacitor generated with the operation of the discharge circuit. A processing circuit for determining a failure of the backup capacitor based on whether it is a predetermined value, wherein the processing circuit includes a booster circuit of the charging circuit when a charging voltage of the backup capacitor is defined by the battery voltage. It is characterized in that it is determined that the portion supplying the voltage is an open fault, and when the discharge voltage of the backup capacitor is defined by a boosted voltage of the battery voltage, the discharge circuit is determined to be an open fault. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. An embodiment according to the present invention will be described with reference to FIG. 1. The configuration is the same as that described in the conventional example, but differs only in the flowchart for performing signal processing of the processing circuit 28. Explaining this, it is added that a judgment on the case where it is judged that the capacitance C1 of the backup capacitor 26 is larger than the specified value is added. That is, when it is determined that the capacitance C1 of the backup capacitor 26 is larger than the reference value, it is determined that the charging circuit or the discharging circuit is in a disconnection state (for example, an open fault of the backflow prevention diode 25 and the switching transistor Tr1). The point is to output a warning signal upon making a judgment.

This will be described with reference to the flowchart of FIG. In FIG. 1, portions performing the same operations as those described in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. That is, when the process proceeds from step 100 to step 200, it is determined whether or not the voltage at the point A has fallen below the reference voltage V1, and if it is determined that the voltage does not drop below the reference voltage V1, the process proceeds to step 210 and the switching transistor It is determined that Tr1 has an open failure, and an alarm signal for notifying the failure is output.
In step 200, the voltage at the point A is changed to the reference voltage V1.
If it is determined that the time is less than the predetermined time, the process proceeds to step 220, in which a timer operation is started to start a time counting operation, and a step 230 is started.
Proceed to.

In step 230, it is determined whether or not the voltage at the point A has further dropped below the reference voltage V2. If it is determined that the voltage has not fallen below the reference voltage V2, the process proceeds to step 240, (3) It is determined that the backflow prevention diode 25 has an open fault and is maintained at a voltage slightly lower than the output voltage of the battery 20, and an alarm signal indicating this is output. On the other hand, when it is determined that the voltage at the point A has fallen below the reference voltage V2, the timer operation is stopped at that timing, the timer operation is stopped, the process proceeds to the next step 130, and the time is measured. If the measured value is smaller than the specified value during the measurement time, an alarm signal is output.

The above description will be described based on the waveforms shown in FIGS. (1) Open Failure of Switching Transistor Tr1 (See FIG. 2) When the ignition switch 24 is turned on and the charging of the backup capacitor 26 is started, the voltage waveform at the point A exceeds the reference voltage V2 at the point a, and further exceeds the reference voltage V2. At this point, the switching transistor Tr1 is turned on in response to the supply of a control signal from the processing circuit 28 and starts discharging.
If there is an open failure, the discharge will not start,
The voltage at the point A does not decrease as indicated by the alternate long and short dash line and maintains the peak voltage. As a result, since the voltage does not fall below the reference voltage V1, the timer does not operate and the switching transistor Tr1 is notified that an open failure has occurred.

(2) Open Failure of Third Backflow Prevention Diode 25 (See FIG. 3) The ignition switch 24 is turned on, and the backup capacitor 26 starts charging through the second backflow prevention diode 23. / DC converter 21 does not charge. As a result, the voltage waveform at the point A exceeds the reference voltage V2 at the point a, but saturates with the voltage divided by the resistors R1, R3 and R4 and cannot exceed the reference voltage V1. Thereafter, the switching transistor Tr1 is turned on to start discharging, and the voltage slightly drops. However, since the charging is continued from the battery 20 via the second backflow prevention diode 23, the voltage at the point A maintains a constant voltage as shown by the solid line. I do. As a result, since the voltage does not fall below the reference voltage V1, the timer does not operate, and it is notified that the third backflow prevention diode 25 has an open failure.

[0017]

As described above, according to the present invention, it is possible to simultaneously diagnose a failure in the capacitance of a backup capacitor and diagnose an open failure in a charge / discharge circuit of the backup capacitor. Is done.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a flowchart of a processing circuit showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a waveform when an open failure occurs in a switching transistor Tr1.

FIG. 3 is an explanatory diagram of waveforms when a third backflow prevention diode 25 has an open failure.

FIG. 4 is a circuit block diagram showing a diagnostic circuit for a backup capacitor 25 used in the occupant protection device and peripheral circuits thereof.

FIG. 5 is an explanatory diagram of a flowchart of a processing circuit for diagnosing a failure of the backup capacitor in FIG. 4;

FIG. 6 is an explanatory diagram of waveforms when the capacity diagnosis of the backup capacitor is performed normally.

[Explanation of symbols]

 Reference Signs List 21 DC / DC converter 22, 23, 25 Backflow prevention diode 26 Backup capacitor 27 Discharge diode 28 Processing circuit Tr1 Switching transistor

Claims (1)

[Claims] 1. A discharge circuit comprising: a backup capacitor; a charging circuit for charging the backup capacitor in parallel with a battery and a boosted voltage of the battery; and a discharge circuit for forcibly discharging the charge stored in the backup capacitor. And calculates the magnitude of the capacitance of the backup capacitor based on the time constant of the charge / discharge waveform of the backup capacitor generated with the operation of the discharge circuit. A processing circuit for performing a failure determination of the backup capacitor based on whether or not there is the backup capacitor, wherein the processing circuit supplies a boosted voltage of the charging circuit when the charging voltage of the backup capacitor is defined by the battery voltage. Is determined to be an open fault, and the discharge voltage of the backup capacitor is A capacity diagnostic circuit for a capacitor, characterized in that when specified by a boosted voltage of the battery voltage, the discharge circuit is determined to have an open failure.