If the line voltage drops between 6 pm and 9 pm, when most people use electricity, appliances like refrigerators and air conditioners use a lot of power. If these appliances don't have a low-voltage cut-off, it will waste electricity and cause the appliances to heat up. In turn, this could make the compressors in these appliances work less well. This circuit is helpful because it turns off an appliance automatically during the busiest times. The appliance will turn back on after three hours. An LDR-based switch is used to turn off the power to a circuit automatically. During the day, LDR1 has a low resistance, so transistor T1 pulls its collector voltage to ground by forward biasing. This keeps T2 from also forward biasing. In this state, the

rest of the circuit is turned off, and the appliance gets power from the normally-closed (N/C) contacts of relay RL1. When the sun goes down around 6 p.m., LDR1's resistance goes up, and transistor T1 stops working. Then, the circuit gets power from the transistor T2. Using preset VR1, you can change how sensitive LDR1 is to the level of light you want. The 14-stage ripple counter CD4060 (IC1) is used to make the timer circuit. Taking pin 1 (Q11) as the output gives a timing of 3 hours. When transistor T2 gives power to IC1, it resets through C1 and R3 and begins to oscillate. The voltage to IC1 is kept stable by the reservoir capacitor C2. This means that small changes in the power supply don't affect the oscillation. The oscillation of IC1 is kept going by resistor R4 and capacitor C3. This is shown by the blinking of LED1 connected to its output pin 7. (Q3). The timer's timeout period can be calculated as follows: T = 2n/fosc in seconds, where n is the number of outputs chosen and fosc = 1/2.3 (R4.C3) Pin 10 of IC1 is connected to the resistor R4, and pin 9 is connected to the capacitor C3. When Q11's output goes high, diode D1 stops IC1 from continuing to oscillate. Q11's output stays high until morning, when IC1 is reset. The timer NE555 is used to make IC2 a bistable latch. Its trigger input pin 2 and threshold input pin 6 are connected so that when the power is turned on, the output of IC2 goes high and latches because its trigger and threshold inputs are both floating. When relay driver transistor T3 conducts, relay RL1 is turned on, which disconnects the appliance, like a refrigerator, from the mains. During the busiest times, this problem lasts for three hours. After IC1's timeout period, its Q11 pin goes high to send a positive pulse through resistor R7 to the threshold input of IC2. This pulse that goes high resets IC2 and makes its output go low. Through the N/C contacts of relay RL1, the appliance is turned on when transistor T3 is turned off and relay RL1 is de-energized. Capacitor C4 keeps the base current of transistor T3 steady so that switching is clean and the relay doesn't chatter. The back emf of the relay is taken away by the freewheeling diode D2. Put the circuit together on any type of PCB and put it in a suitable cabinet. The current

rating of relay contacts should be enough to handle the load. Connect the relay contacts to the AC mains wire using the right-sized wires. Earth the unit correctly and use a three-pin plug to get AC from it. Put the unit where the LDR will get enough light from the sun.