Sunday, July 24, 2016

Main Line Powered LED Pilot Lamp

This is a post about AC main line powered LED lamp with minimum components.

There is not much to write about this circuit so I will try to go a bit deeper and explain how the whole thing works. This circuit can be used with any electrical outlet that does not have a pilot lamp or indicator.

So what do we need for this?

1. A small circuit board to assemble, or you can just solder parts to each other.
2. 0.1uF 400V non polar capacitor, it might read 104 in front of it.
3. 1kohm 1/4W Resistor.
4. 1N4004 diode.
5. LED

That's all!

Circuit Diagram:

How it works? 

Simply the capacitor is dropping the voltage and the resistor is limiting the inrush current. The diode 1N4004 is performing two crucial tasks here. First one is it is limiting the maximum reverse voltage across the LED and the second one is it is providing a path for the negative half cycle so that the capacitor can pass current in both direction. During positive half cycle it will pass through the LED and for the negative one like I mentioned above the diode will be used. If you want to work with lower input voltage just increase the value of the capacitor and that's pretty much it!


This circuit is not isolated from the AC main line so do not touch any part of the circuit without testing even when the power is off.


1. Diode 4004 can be replaced with another LED. Same orientation as the diode.
2. A resistor can be used across the capacitor to discharge it when not in use. 

Hope it will help! Happy Experimenting!

You can read my other posts here.
Learn about Inrush Current.

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