Basic LED question.

Discussion in 'General Electronics Chat' started by tadm123, Apr 12, 2014.

  1. tadm123

    Thread Starter Member

    Nov 20, 2013
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    0
    When I connect the LED's in parallel, and with a resistor in series with the voltage source, I noticed that not all of them light up, just the first ones.
    Wouldn't theoretically all of them light up because they all are in parallel and have the same voltage?

    Thanks in advance.
     
  2. gerty

    AAC Fanatic!

    Aug 30, 2007
    1,153
    304
    All leds are not created equal. Some require higher voltages than others. What voltage are you using, and what color leds are you using?
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Even with a common batch off the same die there will be variations. Manufacters test large batches and group similar LEDs in lots, which is not practical for home use.

    LEDs, 555s, Flashers, and Light Chasers
     
  4. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    We tell people every week that Light Emitting Diodes are not light bulbs, they are not resistors, they are diodes. Diodes have a break over voltage and they are not exactly the same from one diode to the next. The diode with the lowest break over voltage will hog the current. Sometimes it can't hog all the current before the next lowest voltage diode starts to break over into conduction, so a few will light up, but it never ends well unless you can make matched sets like Bill talked about.
     
  5. tadm123

    Thread Starter Member

    Nov 20, 2013
    43
    0
    they are all Red LED's and I'm using a 9V battery in series with a 470 ohm resistor.
     
  6. tadm123

    Thread Starter Member

    Nov 20, 2013
    43
    0
    That was very helpful, thanks.
     
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