Simple power outage self-locking switch circuit

When the power supply from the power grid is normal, it is used like an ordinary switch. Press K1, and the 220V AC power will be divided by R1 and R2 to provide a trigger voltage to the triac, causing the triac to conduct. After the thyristor is turned on, during the positive half cycle of the power supply voltage, a small amount of current charges C through R4 and D, and at the same time the thyristor is triggered by the voltage division of R3 and R2; during the negative half cycle, C discharges to R3 and R2 and triggers the bidirectional SCR, so that the bidirectional thyristor continues to conduct, ensuring the normal operation of the load. Once the power grid suddenly loses power, the charge on C is discharged through R3 and R2. After the power grid is restored, since K1 is normally open and there is no voltage on C, the triac cannot be triggered to conduct, and the circuit is in a disconnected and self-locking state, so no current flows through the load. Only by pressing K1 again can the load work normally, thus effectively preventing waste and accidents caused by restoring power after a power outage. Normally closed button K2 is used to turn off the circuit under normal power supply conditions.