10-10-2012, 01:28 PM
UNDER-VOLTAGE PROTECTION OF ELECTRICAL APPLIANCES
UNDER-VOLTAGE.pptx (Size: 629.36 KB / Downloads: 85)
INTRODUCTION
During peak time line voltage available is less.
This cause wastage of electricity.
This project gives a low cost and powerful solution for this problem.
OBJECTIVES
The circuit protects refrigerators,ACs,microwave ovens as well as other appliances from under voltage.
The project aims to automatically off the electrical appliances when the available voltage is less than 180 V.
COMPARATOR
Operational amplifier IC LM324 is used here as a comparator.
IC LM324 consists of four operational amplifiers,of which only one is used in the circuit.
They operate from a single power supply over a wide range of voltages.
In the under-voltage condition,when the line voltage is below 180V,the voltage at the inverting terminal of op-amp is less than the voltage at the non-inverting terminal.
Thus the output of op-amp goes high and it energises relay through transistor.
ZENER DIODE
Zener diode is an electronic component which can be used to make a voltage regulator circuit.
The unregulated power supply is connected to a 6V zener diode through resistor R3.
VOLTAGE REGULATOR
Voltage regulator IC 7812 is used in the circuit.
This IC is used to give regulated 12V to the relay.
RELAYS
12V SPDT relay is used to control the load.
An NPN transistor is used to drive the relay.The relay is energised through transistor when the output of op-amp goes high.
The AC supply is disconnected and electrical appliances turn off.
PIC AND LCD DISPLAY
The microcontroller used in the circuit is PIC16F877A.
PIC16F877A is interfaced with LCD display to display the value of line voltage available at the mains.