JPS5827871B2 - Capacitor life detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitor life detection device, and particularly to a capacitor life detection device that detects the life of a capacitor based on changes in leakage current.

Electronic devices and the like are generally equipped with various capacitors, but when these capacitors reach the end of their lifespan and leakage current increases, malfunctions and accidents often occur.

In particular, a xenon lamp is flash-discharged using a power supply circuit equipped with a large-capacity electrolytic capacitor or the energy charged in the capacitor, and the luminous energy permanently creates a visible image formed with powder toner on a recording medium. In the charging circuits of facsimile machines, printers, copying machines, etc. that fix images with flash, gas is generated inside the capacitor as the leakage current increases as the capacitor reaches the end of its life, and a capacitor is installed to release this gas to the outside. The problem is that when the safety valve is activated, it makes a loud explosion noise, causing anxiety to the surrounding area, and the scattering of gas has a negative impact on the surrounding circuitry.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a capacitor life detection device that can prevent a decrease in the life of a capacitor, particularly an adverse effect on electronic equipment or the surroundings due to an increase in leakage current.

In order to achieve this purpose, the life detection device according to the present invention stops charging when the charging voltage of the capacitor reaches a predetermined value, and recharges the capacitor when it falls below the predetermined value, thereby keeping the charging voltage almost constant. a capacitor charging circuit that holds the capacitor at a value, and compares a time interval from the stop of charging of the capacitor to the start of recharging with a predetermined time interval, such that the time interval from the stop of charging to the start of recharging of the capacitor is a predetermined time; The charging/discharging time interval monitoring circuit outputs an alarm signal indicating deterioration of capacitor life due to an increase in leakage current when the charging/discharging time interval is shorter than the interval.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a capacitor life detection device according to the present invention, which is roughly divided into a capacitor charging circuit 1 and a charge/discharge time interval monitoring circuit (hereinafter referred to as a monitoring circuit) 2. .

In the capacitor charging circuit 1, a charging capacitor 1c (a capacitor whose life is to be detected) is connected in parallel to a DC power supply 1a via a control switch 1b.

Further, this capacitor 1c is connected to variable resistors 1d and 1, which divide the charging voltage V and obtain a divided voltage vD at the connection point.
The series bodies of e are connected in parallel.

(1) A resistor 1 is connected between the power supply and the ground of the DC power supply 1a.
A Zener diode 1g that generates a predetermined reference voltage Vz is connected through f, and a reference voltage Vz obtained across the Zener diode 1g is input to a comparator 1h.

A divided voltage VD obtained by dividing the charging voltage V of the capacitor 1c by variable resistors 1d and 1e is input to one input of the comparator 1h, and in this comparator 1h, the reference voltage VZ and the divided voltage VD are input. be compared.

Comparator 1h indicates charging stop when Vl)≧Vz.
When the level comparison signal is between VD and Vz, it indicates the start of charging.
(2) Outputs the level comparison signal to the control switch 1b.

The control switch 1b is turned off when the comparison signal cp output from the comparator 1h is at the "L" level, and the capacitor 1C is turned off.
The supply of charging current to is stopped, and the comparison signal cp becomes 1
■When the level is ``, it turns on and starts supplying charging current to the capacitor 1c.

Therefore, this capacitor charging circuit 1 can be considered as a type of constant voltage circuit.

In the monitoring circuit 2, 2a is a monostable multi-by-break that is triggered by the fall of the comparison signal cp output from the comparator 1h and outputs a one-shot pulse M with a pulse width τ, and the pulse width τ is the object of life detection. The leakage current of the capacitor 1c is set to a time width corresponding to the period from the stop of charging to the start of recharging when the leakage current of the capacitor 1c is within a normal range.

2b, the monostable multi-bi break 2a is the comparison signal C0
This is an AND gate that outputs a coincidence signal as an alarm signal A indicating the deterioration of the life of the capacitor 1c when the comparison signal Cp reaches the "Hl+ level" during the output period of the one-shot pulse M after being triggered by the fall of the capacitor 1c. .

The operation of this embodiment will be explained below using the waveform diagram in FIG. 2 and the time chart in FIG. 3.

First, when the power supply switch (not shown) of the DC power supply 1a is turned on, the charging voltage of the capacitor 1c is zero in the initial state, so VD<Vz and the comparator 1h
A comparison signal CP of the H1 level indicating the start of charging is output from the control switch 1b, and a charging current starts to be supplied to the capacitor 1c via the control switch 1b, and the charging voltage V of the capacitor IC reaches the As shown in the waveform diagram in Figure 2, it gradually increases with the passage of time.

Then, at t=t1, when the divided voltage vD by the charging voltage V becomes vD-vz, the comparator 1h connects the capacitor 1
It is determined that the charging voltage v of d has reached a predetermined value, and a comparison signal cp of the "L" level indicating the stop of charging is outputted to the control switch 1b.

Therefore, the control switch 1b is turned off, and the supply of charging current to the capacitor 1c is stopped.

Thereafter, the charging voltage V of the capacitor 1c gradually decreases due to the leakage current of the capacitor 1C and the discharge of the charged charges via the variable resistors id and le.

Then, at t-t2, the divided voltage VD by the charging voltage V becomes V
When D<V2, comparator 1h outputs 'H' indicating the start of charging.
``The level comparison signal Cp is output, and the charging current is again supplied to the capacitor 1c.

Note that the level at which the charging voltage V drops to which the comparator 1h outputs the comparison signal Cp of the "I(" level indicating the start of charging) is determined by the threshold level of the comparison judgment of the comparator 1h, as shown in FIG. In the waveform diagram, this threshold level is shown as Vs.

After that, at the second t3, the divided voltage V due to the charging voltage ■
When D becomes vD=vZ, charging of the capacitor 1c is stopped.

Therefore, the capacitor 1c is connected to the reference voltage Vz and the comparator 1h.
A substantially constant charging voltage V controlled by the above is maintained as the predetermined value Vc.

If the resistance values of the variable resistors 1d and 1e are set in advance in accordance with the normal characteristics of the capacitor 1c whose life is to be detected, the charging/discharging cycle for the capacitor 1c will depend on changes in the leakage current of the capacitor 1c. It will change accordingly.

That is, when the capacitor 1c reaches the end of its life and the leakage current increases, the charging/discharging cycle becomes shorter.

Therefore, by comparing the charging/discharging cycle of the capacitor 1C with that during normal operation, deterioration in the life of the capacitor 1c can be detected.

In this case, the signal indicating the charging/discharging cycle of the capacitor 1c is
Corresponding to the comparison signal cp output from the comparator 1h, the time from when the comparison signal Cp becomes "L++ level" (after charging is stopped) until it becomes "H" level (before recharging starts) Life deterioration can be detected by monitoring the interval T.

FIG. 3a is a waveform diagram of the comparison signal cp output from the comparator 1h, and the "L" level period T1 of this comparison signal Cp
．． T2. T3 becomes shorter as the leakage current of capacitor 1C increases.

This comparison signal Cp is input to the monitoring circuit 2, and the monostable multi-by break 2a is triggered at the falling edge of the comparison signal Cp, and a one-shot pulse M having a predetermined pulse width τ is outputted from the monostable multi-by break 2a. Figure b).

If the "L" level period T1 of the comparison signal cp is longer than the pulse width τ, one input of the AND gate 2b is at the "LIT level" and the other is at the "Hu level, so the AND is not established and the alarm signal is A is not output.

Next, when the "LIT level period T2 of the comparison signal cp becomes shorter than the pulse width τ, as shown in FIG. Output as a signal.

This alarm signal A is used as a 7 drive signal for an alarm display of an electronic device or the like or as a power-off signal for the DC power supply 1a that was charging the capacitor 1c.

As described above, according to this embodiment, with a simple configuration, it is possible to detect the deterioration of the life of a capacitor due to an increase in leakage current, and it is possible to prevent various adverse effects such as explosion of a capacitor or malfunction of electronic equipment due to an increase in leakage current. .

In particular, in this embodiment, since the discharging time of the capacitor 1c is monitored rather than the charging time, even a slight increase in leakage current can be detected.

The reason for this is that the charging current for the capacitor 1c is usually much larger than the leakage current, and therefore the changes that appear in the charging time are extremely small, making it impossible to accurately detect such minute changes.

FIG. 4 is a circuit diagram showing still another embodiment of the present invention, which is applied to a capacitor charging circuit for obtaining flash energy of a xenon lamp or the like.

In this figure, the same parts as in FIG. 1 are designated by the same symbols.

4, the difference from FIG. 3 is that the xenon lamp lighting signal P is connected to the reset terminal (R) of the monostable multi-bi break 2a of the monitoring circuit 2.

Note that a xenon lamp (not shown) is connected in parallel to the capacitor 1c via a xenon lamp lighting switch (not shown), and the charging energy of the capacitor 1c is emitted by the xenon lamp as flash energy.

In the capacitor life detection device configured in this way, the life detection operation based on the increase in leakage current of the capacitor 1c is omitted because it is the same as the circuit diagram in Figure 1, and the operation only when the xenon lamp is lit is shown in Figure 5. This will be explained using a time chart.

First, when charging to the capacitor 1c is stopped at time t1, the monostable multivibrator 2a receives the comparison signal cp
Triggered on the falling edge of

Immediately after this, when the xenon lamp lighting switch is turned on at time t2, the charge in the capacitor 1c is instantly discharged by the xenon lamp.

Then, since the charging voltage of the capacitor 1c becomes zero, the divided voltage VD<the reference voltage Vz, and the comparator 1h again outputs the comparison signal Cp at the "H" level indicating the start of charging at the time 43, but at the time t2. Monostable multi-bi break 2a with
is reset by the xenon lamp lighting signal P.

Therefore, when the xenon lamp is lit, the capacitor 1c
The time interval from charging stop to recharging start is shorter than the normal time interval, but monostable multibibreak 2a
is reset, the AND condition of AND gate 2b is no longer satisfied.

Therefore, the AND gate 2b sends out an alarm signal only when the charging/discharging time interval due to an increase in the leakage current of the capacitor 1c becomes shorter than the predetermined time interval.

Note that the monitoring circuit 2 receives the comparison signal Cp as shown in FIG.
A differentiating circuit 2c that obtains a falling differential signal of , and a timer 2d that starts timing based on the differential signal dCp output from this differentiating circuit 2c and outputs a timer signal when a predetermined time is reached.
and a flip-flop 2f that is set by the differential signal dCp and reset by the OR signal from the OR circuit 2e of the timer signal and the xenon lamp lighting signal P.

As explained above, the capacitor life detection device according to the present invention detects the deterioration of the capacitor life due to an increase in leakage current by monitoring the time interval from the stop of capacitor charging to the restart of charging. .

Therefore, various adverse effects such as explosion of the capacitor or malfunction of electronic equipment due to increase in leakage current can be prevented.

In particular, it has extremely excellent effects such as being able to detect minute changes in leakage current.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the capacitor life detection device according to the present invention, FIG. 2 is a waveform diagram showing the charging voltage of the capacitor, FIG. 3 is a time chart for explaining the life detection operation, and FIG. 4 is a circuit diagram showing another embodiment of the present invention, FIG. 5 is a time chart for explaining the operation of the circuit shown in FIG. 4, and FIG. 6 is a circuit showing another example of the monitoring circuit 2. It is a diagram. 1... Capacitor charging circuit, 1a... DC power supply, 1b... Control switch, 1c...
・Capacitor, 1d. 1e...variable resistor, 1f...resistance,
1g...Zener diode, 1h...
・Comparator, 2... Charge/discharge time interval monitoring circuit (monitoring circuit), 2a... Monostable multivibrator, 2b... AND gate, 2c... -Differential circuit, 2d...timer, 2e...OR circuit, 2f...flip-flop.

Claims (1)

[Claims] 1. A capacitor charging circuit that maintains the charging voltage at a substantially constant value by stopping charging when the charging voltage of the capacitor reaches a predetermined value and recharging when the charging voltage drops below the predetermined value;
The time interval from the stop of charging to the start of recharging of the capacitor is compared with a predetermined time interval, and when the time interval from the stop of charge to the start of recharging is shorter than the predetermined time interval, the life of the capacitor is determined to be deteriorated. 1. A capacitor life detection device, comprising: a charge/discharge time interval monitoring circuit that outputs an alarm signal indicating.