JPH11178194A - Protective circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit for protecting an object, e.g. a high voltage outer unit, against overcorrect or leakage in which restoration after protection is easy and protection against various kinds of abnormality can be obtained using an ibentiral circuit. SOLUTION: An FET Qq is inserted into a feeder line for an object, e.g. a high voltage output circuit X1. Input current is detected by a comparator Qa1 and when an overcurrent flows, a thyristor Qf is turned on by the output from a comparator Qa2 and the FET Qq is turned off. In case of other abnormality, the thyristor Qf is turned on and the FET Qq is turned off to stop power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a protection circuit device particularly suitable for protecting a high-voltage output circuit from overcurrent or the like.

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing a conventional circuit configuration for protecting a high voltage output circuit X1 from overcurrent. In the figure, A1 is a control circuit for switching the FET Q1 to generate a high-voltage AC on the secondary side of the transformer T1, and the generated high-voltage AC is rectified and smoothed by the diode D1 and the capacitor C3 and output. R1 and R2 are resistors, C
1, C2 is a capacitor, and the resistor R2 is a fuse resistor inserted and connected to a power supply line (input line) of the high voltage output circuit X1. Vcc indicates a 24 V input voltage, and GND indicates a ground.

In the above-mentioned circuit, a resistor R2 is interposed as a fuse in the power supply line of the high-voltage output circuit X1 in order to prevent an inrush current at the time of turning on the power and to protect it from an overcurrent.

In this circuit, when the input voltage Vcc is input, it is possible to prevent an excessive rush current from flowing due to the time constant of the resistor R2 and the capacitor C2. Further, even in the case where the FET Q1 is damaged or short-circuited for some other reason, if an excessive current exceeding a certain level flows, the fuse of the resistor R2 is blown and power cannot be supplied, and the output is stopped. You.

As described above, in the related art, a rush current is suppressed by inserting a resistor and suppressing its time constant. For an excessive current, the inserted resistor is cut off and the power supply line is disconnected to protect the rush current. The configuration was taken.

[0006]

However, in the above-mentioned conventional example, the protection is provided by blowing the fuse resistor. Therefore, if the protection has been applied once, the fuse resistor must be replaced. However, there is a problem that it takes time to return.

The present invention has been made to solve such a problem, and provides a protection circuit device which does not require a long time for recovery and which can simultaneously perform other leak protection and the like with the same circuit. It is intended to be.

[0008]

The protection circuit device according to the present invention is constructed as follows.

(1) A switch element interposed in a power supply line to a device to be protected, an overcurrent detection circuit for detecting an overcurrent flowing through the power supply line, and an output from the overcurrent detection circuit It has a control element for controlling the switch element.

(2) In the configuration of the above (1), there is provided an abnormality detection circuit for detecting an abnormality of the device to be protected, and the control element controls the switch element according to the overcurrent detection circuit and the output of the abnormality detection circuit. I made it.

(3) In the configuration of (2), the control element is a thyristor, and the output sides of the overcurrent detection circuit and the abnormality detection circuit are connected to the gates of the thyristors via diodes.

(4) In the configuration of (3), the switch element is an element that is turned on and off by turning on and off the thyristor.

(5) In the configuration of (4), when the overcurrent is detected by the overcurrent detection circuit, the switch element is turned on and off at a high frequency until a certain time, and the overcurrent is continuously generated for a certain time or more. When detected, the switch element is turned off.

[0014]

(Embodiment 1) FIG. 1 is a circuit diagram showing a configuration of a protection circuit device according to Embodiment 1 of the present invention. FIG. 2 is a circuit diagram showing a configuration of a high-voltage output circuit which is a device to be protected. Hereinafter, the configuration and operation of the circuit will be described with reference to the drawings.

In FIG. 1, Qa1 and Qa2 are comparators. Comparator Qa1 constitutes an input current detection circuit for detecting an input current from the voltage across resistor Ra. Comparator Qa2 detects an overcurrent when the input current becomes excessive. It constitutes an overcurrent detection circuit for detection. Qb, Qc, Q
d and Qe are digital transistors, and Qf is a high-voltage output circuit X which is a device to be protected according to the output of the overcurrent detection circuit.
A thyristor (control element) that controls an FET (switch element) Qg interposed in the power supply line to the power supply line 1 has a gate connected to the output side of the comparator Qa2.

In FIG. 1, Rb, Rc, Rd, Re, R
f, Rg, Rh, Ri, Rj, Rk, Rl, Rm are resistors, Ca, Cb, Cc, Cd are capacitors, Da is a diode, ZDa and ZDb are Zener diodes,
Vp indicates a power supply voltage of the high-voltage output circuit X1, Vcc indicates a control input voltage, and GND indicates a ground.

The configuration of the high-voltage output circuit X1 of FIG. 2 is the same as that of the circuit of FIG. 6, and the control circuit A1 turns on (ON) and off (OFF) the FET Q1 to drive the primary side of the transformer T1. Is rectified and smoothed by a diode D1 and a capacitor C3 and output. In the figure, R1 is a resistor, C1, C
2 is a capacitor.

In the circuit configured as described above, to supply power to the high-voltage output circuit X1 (to raise the power supply voltage Vp), a REM signal is input first. As a result, the transistors Qb, Qc, and Qe are turned on, and the FETs are turned on.
Qg is also turned on, and current starts to flow in the power supply line. At this time, a large input current tends to flow until the capacitor C2 in the high-voltage output circuit X1 is charged.

The above input currents are represented by resistors Ra, Rb, Rc,
It is detected by Rd, Re and the comparator Qa1. That is, when the current flowing through the resistor Ra exceeds a predetermined value, the comparator Qa1 becomes “active”. The amount of current flowing through the resistor Ra to make the comparator Qa1 “active” depends on the resistances Ra, Rb,
It can be determined by the values of Rc, Rd, and Re.

When a current larger than the predetermined current flows, the comparator Qa1 becomes "active",
When the transistor Qd turns on and the transistor Qe turns off, the FET Qg turns off. At the same time, the charging of the capacitor Ca starts with the time constant of the resistors Rf and Rg and the capacitor Ca. However, when the current value decreases due to the turning off of the FET Qg, the comparator Qa1 again sets “a
active ”, the FET Qg is turned on, and the input current starts to flow.
The capacitor Ca finishes charging while it is not "live", and discharges at the time constant of the resistance Rh.

By repeating the above operation, the power supply voltage Vp can be raised without flowing an excessive rush current.

Next, protection in the case where an overcurrent flows due to a short circuit due to breakage of a circuit component or other factors will be described.

The short circuit of the high-voltage output circuit X1 includes, for example, a short circuit due to breakage of the FET Q1 in FIG.

Even when the overcurrent flows, the power supply voltage Vp
As in the rise, the overcurrent is suppressed while turning on and off the FET Qg. However, in the case of a short circuit, the overcurrent continuously flows forever. Then, the capacitor Ca charges faster than discharge, the voltage Vca applied to the capacitor Ca eventually becomes higher than the reference voltage Vzda, and the comparator Qa2 becomes “active”. Thereby, the thyristor Qf
Is turned on and the transistor Qe is turned off,
ETQg is turned off, and power supply is cut off. At this time,
Once turned on, thyristor Qf maintains that state.

As described above, protection against overcurrent can be achieved. If an overcurrent happens to occur due to a reason other than component damage, the normal operation can be performed again by turning off / on the REM signal.

As described above, in the present embodiment, it is not necessary to replace the fuse or the like as in the related art, and it takes no time to recover after the overcurrent protection.

(Embodiment 2) FIG. 3 is a circuit diagram showing the configuration of Embodiment 2 of the present invention. The same reference numerals as in FIG. 1 denote the same components.

In this embodiment, the charger E1 in the copying machine is used.
Is connected to a high voltage output circuit X1. Also in this case, the operation at the time of rising of the power supply voltage Vp and the operation related to the short-circuit protection are the same as those described in the first embodiment. However, here, the protection circuit used in the first embodiment is used as it is, so that the protection in the case where the charger E1 leaks can be performed.

In this embodiment, a leak detection circuit B1 is provided in the present embodiment, and when it is determined that a leak has occurred in the charger E1, the output becomes "active".

The output side of the comparator Qa2 and the output side of the leak detection circuit B1 are connected to the gate of the thyristor Qf of FIG. 3 through diodes D11 and D12, respectively. By adopting such a configuration, protection can be applied when either one of the input overcurrent and the leakage of the charger E1 occurs.

(Embodiment 3) In Embodiments 1 and 2, only one high-voltage output circuit X1 is connected. However, as shown in FIG. 4, a plurality of high-voltage output circuits are connected by the same protection circuit. At the same time, and even in the case of other abnormal situations, abnormality detecting circuits (1) F1 to (n) Fn which are configured to be "active" in the event of an abnormality are provided and provided via diodes D21 to D2n, respectively. If this circuit is connected to the gate of the thyristor Qf, various protections can be achieved with this single circuit.

(Embodiment 4) As shown in FIG. 5, if the gate voltage of the thyristor Qf is taken out as an error signal ER, it can be notified that protection has been applied.

While the embodiments of the present invention have been described above, when the FET Qg is inserted into the power supply line as described above and the overcurrent is detected for a short period of time by the input current detection circuit, the FET Qg is momentarily output. Is turned off, and when an overcurrent is detected for a predetermined time or more, or when an abnormality such as leakage of a high voltage output is detected, the FET Qg is kept in the off state to cut off the power supply and turn off / on the REM signal. This makes it possible to return.

That is, at the time of input, overcurrent can be suppressed by the FET Qg inserted into the power supply line, and at the time of abnormality, the FET Qg can be completely turned off to cut off the power supply line, thereby providing protection.

[0035]

As described above, according to the present invention,
It takes no time to recover after overcurrent protection, and
There is an effect that protection in various cases can be performed by the same circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a high-voltage output circuit.

FIG. 3 is a circuit diagram showing a configuration of a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a conventional example.

[Explanation of symbols]

 Qa1 comparator (input current detection circuit) Qa2 comparator (overcurrent detection circuit) Qf thyristor (control element) Qg FET (switch element) X1 high voltage output circuit (protected device) B1 leak detection circuit (abnormality detection circuit) F1 abnormality detection circuit Fn abnormality detection circuit D11 Diode D12 Diode D21 Diode D2n Diode

Claims (5)

[Claims] A switch element interposed in a power supply line to the device to be protected, an overcurrent detection circuit for detecting an overcurrent flowing through the power supply line, and an output terminal of the overcurrent detection circuit. A protection circuit device having a control element for controlling a switch element. 2. An apparatus according to claim 1, further comprising an abnormality detection circuit for detecting an abnormality of the device to be protected, wherein the control element controls the switch element according to an output of the overcurrent detection circuit and the abnormality detection circuit. Protection circuit device. 3. The protection circuit device according to claim 2, wherein the control element is a thyristor, and the output sides of the overcurrent detection circuit and the abnormality detection circuit are respectively connected to the gate of the thyristor via diodes. . 4. The protection circuit device according to claim 3, wherein the switch element is an element that is turned on and off by turning on and off the thyristor. 5. A switch element is turned on and off at a high frequency until a certain time when an overcurrent is detected by an overcurrent detection circuit, and the switch element is turned off when an overcurrent is detected continuously for a certain time or more. 5. The method according to claim 4, wherein
The protection circuit device according to the above.