KR960003419Y1 - Overvoltage protecting circuit - Google Patents

Abstract

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Description

Overvoltage Protection Circuit

1 is a conventional power supply circuit diagram.

2 is a power supply circuit diagram configured with an overvoltage protection circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

1: micom 2: protector

3: power supply IC 4: SMPS transformer

5: flyback transformer 6: relay

7: first bridge rectifier 8: second bridge rectifier

9: fuse 10: first power supply stabilizer

11: second power supply stabilizer 12: third power supply stabilizer

13: fourth power supply stabilizer

The present invention relates to an overvoltage protection circuit, and more particularly, to an overvoltage protection circuit that detects when an output voltage of a power supply circuit is higher than a reference voltage, cuts an output voltage, and automatically returns to normal when a normal voltage is obtained.

A general conventional power supply circuit is shown in FIG. 1 and the operation thereof will be described. An AC power input to the AC plug is voltage-dropped at the transformer T1 and rectified by the second bridge rectifier 8, and then transistor Q2. The first power stabilizer 10 including the resistor R4, the diode D4, and the capacitor C11 is stabilized to generate Vcc4 through the resistor R5. In addition, when the power supply control signal of the microcomputer 1 is supplied to the transistor Q1 through the resistor R1 and the diode D1, the transistor Q1 is turned on to turn on the diode D5 and the relay 6. A current path to the transistor Q1 and ground is formed. Accordingly, since the contact interlocked with the relay 6 is turned on, the AC voltage input to the AC plug terminal is rectified by the first bridge rectifier 7 via the protector 2 which is an overvoltage protection element. The voltage rectified by the first bridge rectifier 7 is converted into a constant voltage by the power supply IC 3 and supplied to the SMPS transformer 4.

The first output voltage output from the SMPS transformer 4 is stabilized in the third power supply stabilizer 12 including the coil L2, the diode D2 'capacitor C5, and the C7 to generate Vcc1 power. The second output voltage output from the SMPS transformer 4 is the second power source including the coils L1 and L3, the diode D2, and the capacitors C3, C4, and C8. It is stabilized at the government 11 to generate Vcc2 power.

On the other hand, the voltage generated by the flyback transformer (FBT) 5 is stabilized in the fourth power supply stabilizer 13 including the resistor R2, the diode D3, the capacitor C10, and the C9, and thus the Vcc3 power supply. Will generate

Here, the diode D6 connected in parallel with the relay 6 is for relay protection, and the capacitor C2 is for noise attenuation. In addition, the capacitor C1 is used for the AC component bypass, and the resistor R3 is for voltage drop.

In the conventional power supply circuit operated as described above, the Vcc2 voltage suddenly rises due to an abnormal phenomenon, whereby the capacitors C4, C8, and C9 explode and damage the peripheral circuit.

Therefore, the present invention detects the above-described Vcc2 voltage and when the voltage is higher than the set voltage, turns off the contact of the relay 6 to discharge the voltage charged in the capacitors C4, C8, and C9. It is an object of the present invention to provide an overvoltage protection circuit that can solve the above disadvantages by turning on the contact of the relay 6 again.

According to the present invention, the first and second bridge rectifiers 7 and 8 for rectifying the input AC voltage, and the first power stabilizer 10 for stabilizing the voltage input from the second bridge rectifier 8. ), A transistor Q1 that is turned on or off in response to a signal input from the microcomputer 1, and the first power supply stabilizer 10 and the first bridge rectifier 7 are connected to each other. Relay 6 for controlling the output of the first bridge rectifier 7 in accordance with an ON and OFF operation, and a voltage via the power supply IC 3 and the SMPS transformer 4 from the first bridge rectifier 7. A power supply circuit comprising a second power stabilizer (11) for stabilizing a voltage, comprising: first voltage distribution means for detecting and distributing an output voltage of the second power stabilizer (7), and the first voltage distribution means The first switch means turned on or off in accordance with the output voltage from the A second voltage distribution means for redistributing a voltage, a second switch means turned on or off in accordance with the second voltage distribution means, and connected between the microcomputer 1 and the second switch means, A diode D7 which passes the power control signal of the microcomputer to ground according to the operation, and is connected between the second switch means and the first power stabilizer 10 to maintain it during the ON operation of the second switch means. An overvoltage protection circuit is provided, characterized in that it is configured as a holding means for the same.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a power supply circuit diagram in which an overvoltage protection circuit according to the present invention is constructed. For example, the Vcc2 voltage is raised above the reference voltage, and the voltage is divided by the resistors R6 and R7. When the voltage divided by the resistors R6 and R7 is higher than the breakdown voltage of the zener diode ZD1, the zener diode ZD1 is conducted and then again divided by the resistors R8 and R9. The divided voltage turns ON the transistor Q3. Therefore, the power supply control signal output from the microcomputer 1 is conducted to the diode D7 is passed to the ground. Therefore, since the low voltage is applied to the base terminal of the transistor Q1, the transistor Q1 is turned off, and the contact of the relay 6 is turned off. Therefore, the rectifying output of the first bridge rectifier 7 is cut off and the voltages charged in the capacitors C4, C8 and C9 are discharged.

When the voltages charged in the capacitors C4, C8, and C9 are discharged, the Zener diode ZD1 is turned OFF because the Vcc2 voltage becomes lower than the reference voltage. Therefore, transistors Q3 and Q4 and diode D7 are turned off. Therefore, the power supply control signal output from the microcomputer 1 causes the transistor Q1 to be turned on again so that the contact point of the relay 6 is turned on.

As described above, according to the present invention, the output voltage of the power supply circuit is detected and the output voltage is cut off when the abnormal voltage is detected, and when the normal voltage is returned to the original voltage, the circuit is protected from overvoltage.

Claims (6)

First and second bridge rectifiers 7 and 8 for rectifying the input AC voltage, a first power stabilizer 10 for stabilizing the voltage input from the second bridge rectifier 8, and a microcomputer 1 is connected between the transistor Q1 that is turned on and off in accordance with a signal input from 1), and the first power supply stabilizer 10 and the first bridge rectifier 7 are connected to the ON / OFF operation of the transistor Q1. Accordingly, a relay 6 controlling the output of the first bridge rectifier 7 and a second voltage stabilized from the first bridge rectifier 7 via the power supply IC 3 and the SMPS transformer 4. A power supply circuit composed of a power supply stabilizer (11), comprising: first voltage distribution means for detecting and distributing an output voltage of the first power supply stabilizer (7), and an output voltage from the first voltage distribution means; According to the first switch means and second voltage for redistributing the voltage via the first switch means. Power supply control of the microcomputer in accordance with the operation of the second switch means, connected between the distribution means, the second switch means turned ON / OFF in accordance with the second voltage distribution means, and the micom 1 and the second switch means. A diode D7 for passing a signal to ground, and a holding means connected between the second switch means and the first power stabilizer 10 to hold it when the second switch means is turned on. Overvoltage protection circuit. 2. A resistor according to claim 1, characterized in that the first voltage distribution means comprises a resistor (R6) connected from the first power stabilizer (7) and a resistor (R7) connected between the resistor (R6) and ground. Overvoltage protection circuit. 2. The overvoltage protection circuit according to claim 1, wherein the first switch means comprises a zener diode (ZD1). 2. The overvoltage of claim 1, wherein the second voltage distribution means comprises a resistor R8 connected from the first switch means and a resistor R9 connected between the resistor R8 and ground. Protection circuit. 2. The overvoltage protection circuit according to claim 1, wherein said second switch means comprises a transistor (Q3). The collector according to claim 1, wherein the holding means includes a resistor R12 connected from the second voltage distribution means R8 and R9, a resistor R11 connected from the second switch Q3 means, and a collector. A terminal is connected to the resistor R12, a base terminal is connected to the resistor R11, an emitter terminal is connected to the first power supply stabilizer 10, and is connected to the second switch means through a resistor R10. An overvoltage protection circuit comprising a transistor (Q4).