low voltage control of AC lighting

Thread Starter

Christopher Gilles

Joined Jan 9, 2016
Hello I'm looking for a simple circuit that I can build to control AC lighting with a DC source. I'm hoping to be able to dim 120 volt lights with a variable 0-12 volts. Basically what I have is a LED controller that can switch/dim LED lights by varying the voltage from 0-12 (DC)volts. I'm hoping to use this device to control a 120volt light. and be able to dim the light using this controller. I've been looking at circuits that use triacs/diacs and photo resistors, opto-isolators, etc. I've not really found a circuit that is really doing what I want to do. Though perhaps someone out there might have a point in the right direction for me. Maybe there is a device that already exists?

I'm thinking it would perhaps be possible to use a standard dimmer and replace the potentiometer with a photo-resistor perhaps?

Anyway, not my area of expertise so I thought I would ask those who may know how to point me in the right direction.

Thanks much :)


Joined May 19, 2014
Here you go. I designed this a few years ago. As the schematic is written, it is set up for 0 to 10 volts in controls 0 to 100% conduction.

If you are interested in building it, I'll go into more detail.



Joined May 19, 2014
It is more power supply than triac controller. Also There was a extra op-amp so I configured it as a differential amplifier. It is a pretty simple circuit other wise.

You will find a far number of single dimmer chips. The problem is that they are not designed to accept a DC control voltage and they are designed to run directly off of the mains. This means the circuit is hot, making it dangerous to deal with.

Anyway here is how the circuit works.
- Q1 is a zero crossing detector that resets the ramp generator U4. This makes a good 0 to 10V linear ramp that is sunk to the line frequency.
- U5 takes your control voltage and inverts it and adds a 10 volt offset to it.
- U4 compares the ramp to the control voltage and triggers the triac when they cross.

Everything is isolated and opto-coupled. It will drive almost any triac.