This paper elaborates the working of a voltage protection unit for electrical appliances. This circuit provides the power to the appliance from the main power supply. Suppose if any voltage fluctuations occur in the main power supply then the circuit gets automatically switched off, by this the electrical appliance gets protected from voltage fluctuations. The entire circuit works on the signals driven from the op-amps. For obtaining we use relays. Depending upon the voltage fluctuations these relays work. In this project we are going to use an op-amp IC LM324 which serves as a comparator. The IC LM324consists of four operational amplifiers but in this design we will make use of only two op-amps.

Circuit designing and working:

Here the input from the main power supply is given to the regulated power supply. The output of the regulated power supply is fed to the op-amp of IC in which we use only op-amp 1 and op-amp2. The  output of this op-amps is given to the transistor circuit. The transistor driver circuit gives the respective pulse to the relay circuit. The electrical appliance is connected to the relay. If the voltage at the inverting terminal is greater then the non inverting terminal then the op-amps makes the relay off. This process  occurs vice versa for less voltages.


This type of equipment is very useful for protecting the appliances against short circuit. We may not get a constant voltage from the power supply and this device works efficiently for the control these disturbances.

Download Over Line and Under Line Voltage Protection for Electrical Appliances Project Abstract.