Spike Guard. Simple Design 25


This Tiny circuit can protect your LCD TV from Voltage surge at power on. It takes 2 minutes delay before connecting power to the TV. Within that time, mains power will become stable. Heavy inrush current at power on or when power resumes after a power failure can damage the TV permanently. If few minutes delay is provided, the AC will become stable. This is the delay technique used in Stabilizers.

Circuit working is simple. 9 Volt power supply is needed for the circuit so use a 9 volt adapter for it. When power is switched on, Capacitor C1 charges slowly through R1 and VR1. When the voltage in the capacitor C1 rises above 3.1 volts, Zener conducts and triggers the Relay driver transistor T1. When T1 conducts, relay energize and provides power to TV. Charging of capacitor and Zener conduction takes around 2 minutes, so relay turns on only after that.
Connect the Phase line to the Common contact of the relay. Phase to the TV should be from the NO (Normally Open) contact of relay. Neutral should go directly to TV. Use a 2 pin socket for connection.