28-07-2011, 11:06 AM
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ABSTRACT:
This circuit protects refrigerators as well as other electrical appliances from over and under voltage. By the name itself we can say that if the input voltage is more or less than the required voltage then the electrical appliance is turned off nothing but it gets disconnected from its respective power supply.
This circuit uses an operational amplifier IC LM324 which is used as a comparator. Generally, the IC LM324 consists of four operational amplifiers, of which only two operational amplifiers are used. In this IC, we have an inverting terminal and a non-inverting terminal. The voltages at the inverting terminal and the non-inverting terminal are 6.0v and 6.8v respectively.
When the input AC voltage exceeds 240v, the voltage at the non-inverting
terminal increases. So now if the voltage at the non-inverting terminal increases more
than 6.8v then the output of the operational amplifier is pulled high. So the electrical
appliance is turned off by means of a relay connected to the output pin of the op-amp.
Thus the electrical appliance is now protected against over voltage. Now let us consider
under voltage condition. When the line voltage is below 180v, the voltage at the inverting
terminal is less than the voltage at the non-inverting terminal. Thus the output of the
operational amplifier now goes high and the AC supply gets disconnected and the
electrical appliance also turns off. Thus, the appliance is now protected against under
voltage.
