220V AC overvoltage protection circuit

As shown in the figure, the protection circuit is controlled by the on/off of the photocoupler. When the voltage is normal, the photocoupler has almost no output, and the VT tube is reverse biased and cut off. When the circuit voltage rises for some reason (neutral line is broken or the neutral line is wrongly connected to the phase line, etc.), the secondary voltage of the sampling circuit rises accordingly, and the photocoupler meets the working conditions. The output current of the photocoupler increases, causing the bias voltage of the VT tube to increase and saturate and conduct, and the actuator relay is activated and attracted, cutting off the power supply to achieve the purpose of protecting the electrical appliance. If the fault is eliminated and the voltage becomes normal, the circuit will immediately stop working and restore the circuit power supply.

Component selection: Optocoupler uses 4N25 or similar. Transistor uses medium power tube 3BG12 or 3BG13. Relay contact uses 5A or above. Coil working voltage can be set by yourself (5V or above to more than 10V). Use light-emitting diode LED as freewheeling tube, which can also be used as indicator. What needs to be modified is the power supply. The primary of the transformer is calculated according to the maximum value of 380V (here it is calculated according to the effective value of the primary 380V). This ensures that once the phase voltage is equal to the line voltage, the device can work normally without damage. The secondary voltage is determined according to the relay coil working voltage. For specific requirements, please refer to the technical requirements of the rectifier circuit.