Hence the op-amp output is zero under this range and thus the relay coil is de-energized and the load is not interrupted during this stable operation.The Potentiometer’s preset VR1 is adjusted such that the voltage at non-inverting is less than 6.8V for stable maintenance of load for the normal supply range of 180V-240V and the voltage of inverting terminal is 6.8V constant due to Zener diode.Overvoltage Protection Circuit using Comparators Similarly, the inverting terminal is also powered through Zener diode and resistance arrangements, as shown in the given under or overvoltage protection circuit. In this circuit, an unregulated power supply is connected to both op-amps terminals, wherein each non-inverting terminal is connected through the two series resistors and a potentiometer arrangement.This operation delivers an error in the output if the input voltage to the comparator crosses the limit beyond the voltage window. Two comparators used as a window comparator formed out of one quad comparator IC.As shown in the above block diagram, the mains AC power supplies the power to the whole circuit and for operating loads by using relays, and also for tripping the load (lamps) in the presence of the input voltage which falls above or below a set value.LM358 op-amp used as comparator, it circuit works with 12V DC supply and consumes 50mA current when Relay is in ON state.Overvoltage and Under Voltage Protection Block Diagram Circuit Operation One pot used to set the high voltage level and another one to set the low level voltage adjust. For this design, the reference voltages are generated with help of two Trimmer potentiometer.

If the signal level is outside of the window, the output is high and Relay is in ON condition. Relay provides normally ON and normally OFF switch. If the signal is within the window, the output is low thus RELAY is in off condition and also LED is off. This circuit utilizes two comparators in parallel to determine if a signal is between two reference voltages.

It employs two comparators to detect over-voltage or under-voltage condition. A window detector circuit, also called window comparator circuit or dual edge limit detector circuit is used to determine whether an unknown input is between two precise reference threshold voltages.

Comparator relay circuit