This main power interruption alarm circuit constructed with few simple components and this circuit gives long buzzer beep sound when the main power supply interrupted.
Circuit diagram for main power interruption alarm
Construction and Working
Main power supply 230 volt step downed by the transformer to 9 volt AC and rectified by the half wave rectifier and then rectified DC voltage is applied to the Q1 and Q2 transistors, here these two transistors acts as a switch in order to disconnect the buzzer from the power supply while the main power supply presence.
If the main power supply interrupted means buzzer and Q2 transistor switch gets enough supply through the capacitor C2 and C3 hence the buzzer gives beep sound throughout the presence of c2 & c3 capacitor charge.
If the main power supply came in means the Q2 transistor base connected to the ground through Q1 that is Q2 open hence no buzzer sound.