High Voltage powering RGB LEDs

Discussion in 'The Projects Forum' started by tonytuba, Mar 8, 2010.

  1. tonytuba

    Thread Starter New Member

    Mar 8, 2010
    Hi all,

    First post on this forum and I'm a bit of an electronics newb. I started writing long post, but will just give details and if you'd like the full version, let me know.

    I'm modding a DMX LED color changing light so that it uses RGB LEDs.

    There's a 4 pin connector that bridges the power/DMX circuit and the LED board.

    Max voltage for RG&B - 14.5 Volts

    MY RGB LEDs:
    Forward Voltages - Red-2.0, Blue-3.5, Green-3.5
    Forward Current - 30ma
    Common - Cathode

    I have calculated for the correct resistors and I am aware that the current draw multiplies per how many LEDS I connect together. I know I muse run these in parallel and that the original circuit was designed to power LEDs in series.

    Any ideas on this one?
    Should I have gotten Common Anode?
    Should I dig further back on the DMX board and pull signal from there?
    Do I need to boost the current coming from the DMX board?
    What is the average air speed of a laden African Swallow?

    Again, I will be more than happy to answer any questions if it will shed light on a solution.

    Tony :cool:
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    What IS the average airspeed of a Laden African Swallow?

    If the 4th pin is providing the 14.5v, That would be where the anodes would connect, in your case, you have a common cathode, so thats not to good. You would be reverse bias your LEDs. They don't work that way. Your VDD is the supply voltage, for common cathode RGB LEDs, you will need three VDD's. and a common ground.
  3. Wendy


    Mar 24, 2008
  4. tonytuba

    Thread Starter New Member

    Mar 8, 2010
    @retched - I'm fearing that the anobe/cathode issue is the source of my problem. I've tried a multitude of circuit designs, all with the same result, no light. Also, thank you for shedding light on how the vdd works. I was thinking the opposite, that the RGB carry the voltage and the VDD was the ground. Again, noob :) I'll reorder new LEDs, try again, and post my results. Should be a couple days. If this works, I have lots of lights to mod out.

    Also, I'm looking at building my own moving head lights using some decent stepper motors and a couple high powered LEDs. Again, it will be a similar board design, multiple RGB LEDs that will all be the same color at once. However, I'd like to get these working first.

    @Bill - Thank for the link to that post, it looks like there's a lot of good info in there, especially the idea about putting an LM317 on the circuit to regulate the current. I'll be reading the rest of it shortly.

    As far as your question, DMX is the industry standard for lighting communication, in live and theatrical venues. The lights I have are small cans about 4-5" in diameter, about 4" deep. They have a DMX in/out, chainable power and are relatively cheap. Since they are so cheap, the LEDs in there are all individual Reds, Blues and Greens. And, since they are individual colors, they are all wired in series, which explains the high voiltage. The DMX allows me to communicate with the lights, telling them intensity, color, and on more advanced lights, x/y coordinates, focus, gobos, etc...

    I've done theatre lighting for over 10 years now and only as of the last few years with the advent of LED lighting, can Joe Everyguy afford these lights. I've been throwing living room and basement parties, with at least 11 lights that all fit in a rollable bin and people are loving it. Being able to light your house for a party, only needing one outlet and not raising the room temp to 200 degrees is fantastic. Anyhow, I'll stop ranting ....
  5. Wendy


    Mar 24, 2008
    The new high power LEDs are as bright as incandescents. They take .7A up to 3A (depends on what you buy). They get a little warn, but nothing compared to incandescents. In terms of efficiency they rate against fluorescents about the same as fluorescents rate against incandescents.

    They tend to be a little expensive though, but you can light a room with them.

    If you have any special projects I'll try to help out. I'm spread pretty thin, but I like this kind of stuff.