Multipurpose power outage alarm circuit

How the circuit works: This is an AC fuse blown alarm. When BX is not
fused , the 220 V AC voltage is rectified by VD1-VD4 bridge, R1 current-limiting and step-down,
DW stabilized, and C1 filtered to form a 6V DC voltage, which is added to the power switch through R2 and VD5 (for isolation
) Pin 4 of the integrated circuit TWH8778 makes pin 4 high
level, TWH8778 is cut off and does not work, and the speaker does not make sound.