Circuit principle of acousto-optic power failure alarm

The circuit principle of acousto-optic power failure alarm is as follows:

The acousto-optic power-off alarm turns on the power switch. After the AC voltage of 220V is reduced, rectified and filtered by the transformer, the DC voltage of 12V is output and supplied to the circuits of IC 1 and IC2. When the input power is normal, LED 1 lights up, driving IC 1 controlling IC2 does not act, and the alarm does not emit any sound and light.

Cut off the input power supply, the voltage of 12V disappears, and IC 1 loses its working voltage and stops working. At this time, the oscillator composed of IC2 began to oscillate, driving IC3 and IC4 to work, and gave an audible and visual alarm.