LED dimmer question

Discussion in 'The Projects Forum' started by tdietz20, Jun 24, 2014.

  1. tdietz20

    Thread Starter New Member

    Mar 7, 2011
    First off let me assure you that I've noted in the TOS the restriction on of discussing "LED to mains" but I hope this question has a potential solution that doesn't necessarily require that.

    I have a significant amount of experience doing house wiring (all inspected by my electrician brother and passed DBI inspection), and I've done a bit amount of electronic circuit building, a bunch of LED projects ranging from small to large and goofy (https://www.facebook.com/tiefighterartcar/photos_stream) . I am fully conscious and wary of being in the "know enough to be dangerous" position and hope that I approach ideas and projects like this with the appropriate respect. So if this idea is completely infeasible or just dangerous please just say so without calling me crazy, ignorant, or stupid. This is why I'm asking first.

    What I'd like to build is an ceiling light fixture using LED, ideally 12V LED strip for convenience. I'd like this fixture to be dimmable, but would prefer PWM dimming because the particular strip that I prefer using (same as I've used under my kitchen cabinets), gets color distorted using simple voltage dimmers.

    I could do this very simply by using a similar controller that I've used elsewhere, but I'd really like to be able to leverage the same dimmer switch I use with my home automation setup so I could control it from the same point, which is a standard incandescent dimmer.

    So in the end what I was hoping to find is a solution that can go straight into the ceiling fixture box, a device that will translate a change in AC main voltage transformed into a corresponding PWM signal to an LED.
    If PWM isn't possible I'd settle for a simple voltage dimming.

    I'd be thrilled if there was some sort of off the shelf solution, but if not I would love to hear if it's even possible to build such a thing and if were safe if done by a qualified person.

    Again, I sincerely apologize if this blatantly violates the site's policy of not offering advice on connecting LED to mains.
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    The "LED to mains" is only an issue if you don't want to use a transformer to step down the voltage and instead attempt with capacitors/resistors only.

    Since you want 12V LED strips you can simply use a 12V ac to dc converter and the TOS is not an issue.
    They make nice wall switch dimmers for those too like this that do pwm http://www.superbrightleds.com/more...and-dimmer-for-standard-wall-switch-box/1181/
    and a simply 12v power supply like this

    BUT... (this takes away the DIY aspect though)
    You could also just buy a Cree (or other but Cree is by far superior to many of the other s out there now) LED bulb from home depot and use it just like a regular light bulb and be done.
    Like this and it can be dimmed with a standard dimmer switch and screwed into a regular light bulb socket..
  3. tdietz20

    Thread Starter New Member

    Mar 7, 2011
    Yeah you're probably right. I've used the Cree bulbs before and I love the fact that they make the warmest color temp LED bulb out there that I've seen. But for this project i was really hoping to use LED strip as it suits the design I was going for, a wide low profile type of thing. Don't think I can place lights and diffuse them the way I wanted with big bulbs.

    Before I resort to that I am still holding out hope I can find some way to translate a change in AC voltage to a corresponding change in DC voltage in the range for dimming those lights. not sure if translating a change in AC to a PWM signal is a pipe dream.
  4. wayneh


    Sep 9, 2010
    You didn't say what sort of AC dimmer you are using. Are you sure it's dimming by delivering a reduced voltage? Someone will jump in and correct me, but I believe for a standard dimmer the voltage stays the same but the waveform gets truncated, reducing the delivered power.

    I think you could detect the wave shape on the DC side of a transformer, and convert it to the PWM signal you need. But success depends on knowing what you are starting with.
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Yep, that's how they work. You would have to design an AC to 12 VDC converter that maintains the 12V while the AC is reduced, and also reads the AC value to produce the PWM.

    Not completely impossible as long as you realize you can dim the AC to the point the LEDs have to turn off. But you still should get a minimum of 50% voltage control, perhaps up to 75%