Overvoltage automatic power-off device

This article introduces an overvoltage protection circuit made by the switching integrated circuit TWH8778, which can avoid the danger caused by excessive mains voltage. The circuit principle is shown in the attached figure. The 220V mains power provides a stable 12V working voltage for the switch integrated circuit through C1, VD1, and DW1. VD3, R2, and RP1 form a voltage dividing sampling circuit. When the mains voltage is normal, DW2 cannot conduct, the working voltage of pin 5 of TWH8778 is lower than 1.6V, relay J does not pull in, and the mains supplies normal power to the CZ socket through the J-1 normally closed contact; when the mains voltage is high When out of the normal setting, DW2 breaks down and conducts, the potential of pin ⑤ of TWH8778 rises to 1.6V, causing the IC to flip, pin ③ outputs high level, the relay is closed, and the power supply of the electrical appliance is cut off immediately, thus avoiding overvoltage. Hazards caused by using electrical appliances. After the device is welded correctly, connect the mains power to the input end of the voltage regulator, and carefully adjust RP1 with the voltage regulator so that relay J closes when the voltage is 240V. Then connect the circuit to the mains power grid and it can work normally. .