This circuit can protect your electronic devices like TV against surge current . Very high spikes can occur when power is turned on due to sparks in the switch and more serious effects occur when power is resumed after a power failure due to the high magnetic field in the distribution transformer. When we keep the TV in standby mode using the remote control, this high inrush current when the power is resumed can cause permanent damage.
Figure 1: Circumference Image for Electronic Device Cables
This circuit gives a delay of 1 minute before turning on the TV. After this delay, a Green LED lights up and we can manually activate the relay using pressure switch S1. The relay activates and connects power to the TV. When power fails and restarts, the relay remains de-energized until S1 is manually pressed.
Fig. 2: Circuit diagram for electronic protection for protecting electronic devices
The circuit uses a voltage comparator built around IC1 (CA3140). Its inverting input is connected to a potential divider R2, R3 that provides half the supply voltage (4.5 volts) to the inverting input. The non-inverting input is connected at the junction of R1 and C1. When the power is turned on, the output of IC1 will be low and the capacitor C1 will be charged through R1. When it is fully charged, the voltage at pin 3 rises above that of pin 2 and the comparator gives a high output and the green LED lights up. The time delay depends on the value of C1 and the given value; it will be around 1 minute. When S1 is pressed and released, the SCR is activated and the relay is energized to power the TV through the Common and NO contacts. The SCR remains locked even after its gate chain is removed by releasing S1. Red LED indicates charge activated status.