Mains undervoltage and voltage loss protection circuit

It can be used for refrigerator
protection. It uses 7815 three-terminal fixed integrated voltage regulator
Ai and 555 time base integrated circuit Az ( monostable circuit for
delay control).
    When the mains power is lower than 180V, the relay KA is released, cutting off the load power supply, and the light-emitting diode VL lights up at the same time. When
the power supply is restored after a power outage, the protection circuit will take 3-5 minutes (set by the potentiometer RP) to make KA close.