Electronic Guard to Protect Electronic Devices

This circuit can protect your Electronic devices like TV from inrush current. Very high spikes can develop at power on due to sparking in the switch and more serious effects occur when power resumes after a power failure due to high magnetic field in the distribution transformer. When we keep the TV in standby mode through remote, this high inrush current when power resumes can cause its permanent damage.

Protect Electronic Devices

This circuit gives a time delay of 1 minute before giving power to the TV. After this delay, a Green LED turns on and we can manually trigger the relay through the press switch S1. Relay activates and connects power to the TV. When power fails and resumes, Relay remains de-energized till S1 is pressed manually.

The circuit uses a voltage comparator built around IC1 (CA3140). Its Inverting input is connected to a potential divider R2, R3 that provides half supply voltage (4.5 volts) to the inverting input. The non inverting input is connected at the junction of R1 and C1. When power is switched on, output of IC1 will be low and capacitor C1charges through R1. When it charges fully, the voltage at pin 3 increases above that ofpin2 and the comparator gives a high output and Green LED turns on. Time delay depends on the value of C1 and with the given value; it will be around 1 minute. When S1 is pressed and released, SCR triggers and relay energizes to power the TV through the Common and NO contacts. SCR remains latched even after its gate current is removed by releasing S1. Red LED indicates the Load On status.