help!!!!!

Discussion in 'General Electronics Chat' started by Dandiaz, Apr 10, 2014.

  1. Dandiaz

    Thread Starter New Member

    Apr 8, 2014
    1
    0
    new to the site thank you; I constructed a led sign COCKTAILS having a
    major problem burning up leds. using a pc power supply 3.8 vdc 18Amp
    uln2003a each letter uses 50-80 leds can someone help.
     
  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,793
    829
    Schematic, schematic, schematic! Go to advanced mode and attach your images. Note that LNG is preferred; jpg files are blurry.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,420
    3,355
    help!!!!!

    Your title is of no use to readers.

    Use a title that provides more information about your request.

    If you are experiencing a bug related to having long subject titles, simply let us know the title you would prefer.
     
  4. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,136
    200
    My crystal ball doesn't see a resistor between each LED. A LED is a current driven device,

    So, the series resistor is R= (Vsupply-Vf)/Iled

    The last term is I led. Vf is the NOMINAL operating current and is generally different for each color.

    The wattage of the series resistor is > I^2*R

    The larger LED lamps use a currrent regulator which makes the light output less sensitive to temperature.

    Oh, you can string the LED's in series. You just have to total up all of the nominal forward voltages.
     
    Zerotolerance likes this.
  5. Little Ghostman

    Member

    Jan 1, 2014
    294
    97
    We must have the same crystal ball! 18Amps no resistor Hmmm tough one this, but I am also going to guess each Led is getting a tad too much current.
     
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