Working principle circuit diagram of refrigerator protector composed of TWH8751

This fully automatic refrigerator protector has a simple circuit, complete functions, reliable and sensitive action, and is a useful accessory for refrigerator use. The circuit diagram is shown below. When the voltage of the 220V mains power grid is too low, which may damage the refrigerator motor, the voltage division values ​​of R1 and RP1 decrease, causing VD5 to conduct, causing the integrated circuit IC to conduct, and then VD7 to cut off, and then the triac VS Shut down to cut off the power of the refrigerator. Adjust RP1 to set the undervoltage protection value. When the grid voltage is too high, the refrigerator motor may overheat and burn out. This is because the divided voltage value of R2 and RP2 increases, causing the transistor VT to conduct, and then VD6 conducts, and then IC1 conducts, causing VD7 to cut off, and the thyristor VS to turn off. Overvoltage protection can be set by adjusting RP2, and R7 and C2 form a power-off delay start circuit. When the power is turned on immediately after a power outage, the voltage at both ends of C2 cannot change suddenly, causing IC1② pin to protect the low level and conduct, thus cutting off VD7 and VS, thus protecting the refrigerator compressor. The delay time is determined by the values ​​of R7 and C2. According to the value in the figure, the delay time is about 6 minutes.

See the table below for the component list.