Fully automatic refrigerator protector

Fully Automatic Refrigerator Protector This fully automatic refrigerator protector has a simple circuit, complete functions, reliable and sensitive action, and is a useful accessory for refrigerator use. working principle    　　

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 turn on, and then VD6 turns on, and then IC1 turns on, making VD7 cut off, and the thyristor VS turns off. Adjust RP2 to set the overvoltage protection value. 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. The component selection and production component list is shown in the table below. No. Name Model Quantity R1, R2, R3 Resistor 10K 1/8W 3 R4, R5 Resistor 270Ω 1/8W 2 R6 Resistor 100Ω 1/8W 1 R7 Resistor 4M 1/8W 1 C1, C2 Electrolytic capacitor 470u/25V 2 C3 Polyester capacitor 0.1u/600V 1 RP1, RP2 trimming resistor 1K 2 VD1－VD7 rectifier diode IN4001 7 VT transistor switch type such as 3DK2C, etc. 1 VS triac 8－10A ≥600V 1 IC high power switch IC TWH8751 1 T power transformer Level voltage 15V, power 5W 1 The production and debugging of this protector are very simple, so no details are given. When adjusting RP1 and RP2, an AC voltage regulator can be used to simulate the changes in the mains voltage.