JPH06331668A - Calculating circuit for capacity of capacitor having built-in dc/dc converter - Google Patents

Abstract

PURPOSE:To achieve cost reduction by providing the output means of a DC/DC converter with a capacitor, and detecting an upward change in voltage in a predetermined time. CONSTITUTION:When an ignition switch 2 is turned on, operation of an oscillating circuit 5 is initiated to start charging a backup capacitor 11, and an AND gate 15 is opened so that a counter 16 starts counting pulses output from the oscillating circuit 5. A predetermined period of time after counting of the pulses has been started, a signal for reading the voltage V1 of the capacitor 11 is supplied to an arithmetic processing circuit 13' from the counter 16, and a signal for reading voltage V3 is supplied after a predetermined period of time has further elapsed. These two voltage values V1, V3 are read by the arithmetic processing circuit 13' and the normality or abnormality of the capacitor 11 is determined from the voltage difference. Since the capacitor 11 is incorporated into the DC/DC converter 7, the overall constitution of the capacitor is simplified and the cost is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter for calculating the capacity of a capacitor incorporated in a DC / DC converter in an airbag system or the like provided in an automobile or the like.
The present invention relates to a capacitance calculation circuit for a capacitor with a built-in / DC converter.

[0002]

2. Description of the Related Art FIG. 3 shows a circuit configuration block diagram of a backup capacitor capacity calculation circuit in a conventional air bag system, and a conventional capacitor capacity calculation circuit will be described. In the figure, the voltage of a battery 1 as a DC power source is passed through an ignition switch 2, a backflow prevention diode 8, two acceleration switches 41 and 43 which are closed by a shock such as acceleration, and ignition powder for activating an airbag. The detonator 42 is connected in series. On the other hand, the current flowing through the backflow prevention diode 8 is supplied to the backup capacitor 11 via the resistor 10.

DC / DC is output from the battery 1
The voltage boosted by the converter 7 is applied to the connection point between the backflow prevention diode 8 and the resistor 10 via the backflow prevention diode 9, and is supplied to the backup capacitor 11 via the resistor 10 to initialize the backup capacitor 11. Charge from zero charge. Further, the output of the DC / DC converter 7 via the backflow prevention diode 9 is also supplied to the series circuit of the two acceleration switches 41 and 43 and the detonator 42.

The DC / DC converter 7 is composed of a coil 4, a switching transistor 6 and an oscillating circuit 5, and the coil is turned on and off according to the on / off control of the pulse output from the oscillating circuit 5. The current flowing in 4 changes and the input voltage is boosted.

In this state, when the vehicle body collides, the two acceleration switches 4 connected in series to the detonator 42 are connected.
The currents from the battery 1 are switched to the ignition switch 2 and the backflow prevention diode 8 by closing the switches 1 and 43.
Flows to the detonator 42 through the series. As a result, gunpowder is ignited, and the explosive force inflates the airbag to protect the driver.

However, if the voltage of the battery 1 is lowered or the DC / DC converter 7 is out of order, a collision causes the two acceleration switches 41 and 43.
When is closed, the electric charge charged in the backup capacitor 11 is discharged, and the discharge current flows through the diode 12 to the detonator 42 to ignite the explosive charge.

Thus, the backup capacitor 11
Is used as a backup power source, and it is extremely important to check whether or not the capacity of the backup capacitor 11 is equal to or larger than a specified value. As a conventional method of calculating the capacity of the backup capacitor 11 as this checking method, for example, as shown in FIG. 4, the voltage on the non-grounded side of the backup capacitor 11 after the ignition switch 2 is turned ON, that is, the charging voltage is calculated. Measure with circuit 13. In other words, the arithmetic processing circuit 13 measures the time t1 from when the charged electric charge becomes zero to the reference voltage V1 and calculates the capacitance value of the backup capacitor 11 by the following equation (1).

[0008]

[Equation 1]

As a result, if the calculated capacitance value is within the predetermined range, the backup capacitor 11 is judged to be normal, and if it is out of the range, it is judged to be abnormal and the alarm signal A is output.

[0010]

However, the above-described conventional capacitor capacity calculation circuit is configured to measure the charging voltage from the state where the charging voltage of the backup capacitor is zero immediately after the ignition switch is turned on. However, there has been a problem that the scale of the program for the arithmetic processing circuit, that is, the program for performing the calculation of Formula 1 becomes large, and the cost becomes high.

The present invention has been made in view of the above problems, and an object thereof is to provide a low cost DC / DC converter built-in capacitor capacitance calculation circuit.

[0012]

DC / DC according to the present invention
The capacitance calculation circuit of the DC converter built-in capacitor includes a DC / DC converter that intermittently repeats on / off and boosts the voltage boosted by the coil to which the voltage is supplied by the capacitor to be measured and outputs the boosted voltage. And an arithmetic processing circuit for calculating the capacity of the capacitor according to the amount of electricity boosted by the capacitor during a predetermined time after the start of boosting of the DC / DC converter.

[0013]

According to the present invention, a capacitor is provided in the output stage of the DC / DC converter, the capacitor is charged with a constant current to boost the voltage, and a change in the boosted voltage of the capacitor within a predetermined time is detected. The cost was reduced by adopting the configuration.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below with reference to FIG. In FIG. 1, the same or equivalent components as those of the conventional example shown in FIG. 3 are designated by the same reference numerals, detailed description thereof will be omitted, and only different portions will be described.

In FIG. 1, reference numeral 15 denotes an AND gate, which receives a pulse of a predetermined frequency supplied from the oscillation circuit 5 and an output voltage of the ignition switch 2,
When the high level signal is supplied from the ignition switch 2, the pulse from the oscillation circuit 15 is passed.
Reference numeral 16 denotes a counter, which counts the pulses supplied from the AND gate 15, and when the count value of the pulses reaches a predetermined value, that is, when t0 time elapses, the backup capacitor 11 of the backup capacitor 11 is provided to the arithmetic processing circuit 13 '. A signal for reading the charging voltage V1 is output. Further, when a time t1 is reached after a lapse of a predetermined time, a signal for reading the charging voltage V3 of the backup capacitor 11 is supplied to the arithmetic processing circuit 13 '.

As a result, the arithmetic processing circuit 13 'takes the difference between the two read values V1 and V2, and when the value deviates from the set reference value, it is determined that the capacity is defective and the alarm signal A is output.
Is output.

Next, the operation of the above structure will be described with reference to FIG. That is, when the ignition switch 2 is turned on, the operation of the oscillation circuit 5 is started, the backup capacitor 11 is started to be charged, and the AND gate 15 is opened and the pulse output from the oscillation circuit 5 by the counter 16 is output. Counting is started. When a predetermined time has elapsed from the start of the counting of this pulse and time t0 is reached, a signal for reading the voltage V1 of the backup capacitor 11 is supplied from the counter 16 to the arithmetic processing circuit 13 ', and further time elapses. When the time t1 is reached, a signal for reading the voltage V3 is supplied, these two voltage values V1 and V3 are read by the arithmetic processing circuit 13 ', and the normality or abnormality of the backup capacitor 11 is determined from the voltage difference, and an abnormality is detected. If it is determined that the operation signal is output, the arithmetic processing circuit 13 'outputs an alarm signal A.

[0018]

As described above, according to the present invention,
Since the backup capacitor is incorporated in the DC / DC converter, the overall configuration is simplified and the cost is reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration block diagram for explaining an embodiment of a capacitance calculation circuit for a DC / DC converter built-in capacitor according to the present invention.

FIG. 2 is a backup capacitor 1 for explaining the operation of FIG.
It is a charging voltage waveform diagram of No. 1.

FIG. 3 is a circuit configuration block diagram of a capacitor capacitance calculation circuit showing a conventional example.

FIG. 4 is a backup capacitor 1 for explaining the operation of FIG.
It is a charging voltage waveform diagram of No. 1.

[Explanation of symbols]

 5 oscillator circuit 6 switching transistor 7 DC / DC converter 11 backup capacitor 13, 13 'arithmetic processing circuit 15 AND gate 16 counter

Claims (1)

[Claims] 1. A coil (4) to which an electric current is intermittently supplied.
The voltage boosted by the capacitor (11) is smoothed by the capacitor (11), and in the DC / DC converter (7) that outputs the smoothed boosted voltage, the capacitor (11) ) Is provided with an arithmetic processing circuit (13) for calculating the capacity of the capacitor with an electric quantity boosted by DC / DC.
Capacitance calculation circuit for the DC converter built-in capacitor.