Over & Under Voltage & Short Circuit Protection of Electrical Appliance

Abstract-The aim of this project sudden fluctuation in supply is a very big problem in industries and domestic applications. It causes a major loss for industries, offices and homes. This project gives a low cost and powerful solution for this problem. This Circuit protects refrigerators ACs, Microwave ovens as well as other appliances from over and under voltage fluctuations. Operational amplifier IC LM324 is used here as a comparator. The preset is adjusted such that for the normal supply of 180V to 240V, the voltage at non-inverting terminal of op-amp is less than 6.8V. The same unregulated supply is given to the second comparator through a 5.6V zener diode. 12V SPDT relay is used to control the Load. An NPN transistor is used to drive the relay. This project uses regulated 12V, 500mA power supply. 7812 three terminal voltage regulator is used for supply voltages and reference voltages for LM324 comparator circuit. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/12V step down transformer. Index Terms- short circuit protection, saving energy, home appliance protection.