LED Dimming with Triac Dimmer

Discussion in 'The Projects Forum' started by oldschoolcivic, Apr 21, 2010.

  1. oldschoolcivic

    Thread Starter New Member

    Mar 23, 2010
    I have several rolls or LED tape lighting. The lights need to be dimmed with a RF controlled dimmer, which is a leading edge (triac) type dimmer.The specifics for the lights is limited but here is what I have:

    -The lights are intended for a constant voltage (12v) power supply
    -When hooked up to a 12v power supply it draws about 2A
    -Each led has a resistor associated with it but the tape is covered in a
    plastic coating for protection and I can't see the circuit layout.
    -The roll is pretty long and has a bunch of LED's on it. I haven't counted all
    of them yet

    So long story short, I got this to work quit well but there is a problem.

    To get this to work I connected the the dimmer to a 10:1 transformer from there I connected the secondary to a rectifier and on to the LED. At first this would not work, by this I mean that the lights would pulse in a dimming fashion. I then hooked up the O-scope and checked a few points. I found that the signal was severely messed up. Basically there was no stable output from the dimmer circuit.

    So I had an idea, maybe the dimmer circuit is looking for a load (lightbulb). I got the idea to wire up a standard incandescent in parallel with the primary side of the transformer. TADA it works. The output from the dimmer circuit became steady and I could monitor the leading edge shift with the adjustment of the dimmer. The LEDs dimmed perfect with no flicker and seem to have a pretty large range of diming.

    Who wants to run a lightbulb when the goal is LEDs. So this is where I am stuck. What can I do to take that lightbulb out of the mix. Oh I even tried replacing the lightbulb with a resistor and that also worked but same I^2R problem as the lightbulb.

    Any suggsted circuits or reading or ideas would be a great help

    Thanks very much
  2. SgtWookie


    Jul 17, 2007
    Forget using the dimmer on the mains side.

    Use a PWM circuit on the DC side.
  3. oldschoolcivic

    Thread Starter New Member

    Mar 23, 2010
    Needs to be the RF controlled triac dimmer
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    What is the manufacturer of the LED tape? and the model? I have seen the LED rope lighting that required triac dimmers. The frequency to current circuit was IN the rope.

    This was direct replacement lighting for old incandescent rope lighting that we were using for sculptured lighting. This way, the led rope would work as a direct replacement with the animation controls that already existed.