OVERVOLTAGE And UNDERVOLTAGE PROTECTION For Electrical Appliances

In some places, especially in developing countries like ours, sudden ups and downs in the mains voltage are quite common.

- SHAMAIL AHMAD

This sometimes causes a serious failure of electrical appliances like television sets, air-conditioners, and refrigerators, which are not designed to tolerate lower or higher voltages beyond a small limit.

This circuit incorporates a low-voltage and high-voltage tripping mechanism to protect the appliances from any damage due to voltage fluctuation. The author's prototype on the breadboard is shown in Fig. 1. The circuit diagram is shown in Fig. 2.

The circuit's dual power supply using transformer X1 and diodes D1 through D4 isolates the supply between relay RL1 and control circuitry with the help of optocoupler IC PC817. It helps to eliminate the voltage-dropping problem when the relay energises. The capacitors C1, C2, and C3 are used to smoothen the rectified pulsating DC from the diodes.