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Discussion in 'General Electronics Discussion' started by davez, Aug 3, 2015.

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  1. davez

    davez

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    0
    Oct 11, 2014
    I tried hooking up an led directly to a 9v battery(hahaha)
    but what happened is it kinda switch color from red to dark orange then dies can someone give a good explanation why this happens
     
  2. Tha fios agaibh

    Tha fios agaibh

    2,096
    703
    Aug 11, 2014
    Too much power blew it up.
    A red led runs on about 2 volts and draws about 20ma.(depending on led)
    If you want to run it on a 9v battery, the current needs to be limited. If you add a resistor that drops the voltage difference you would get (form ohms law); 7volts divided by .02amps that equals 350ohms. So a 350ohm resistor would limit the current and cause 7volts to drop across it, leaving 2v for the led.
     
  3. Gryd3

    Gryd3

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    Jun 25, 2014
    I think the op was asking why it changed color as it died?

    I've noticed too, and if this is indeed the questions, I'm unsure myself and a little curious.
     
  4. davenn

    davenn Moderator

    13,589
    1,871
    Sep 5, 2009
    for the same reason my meat under the grill goes from red to brown to a charred black
    if subjected to too much "power" ;)
     
    Martaine2005 likes this.
  5. Martaine2005

    Martaine2005

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    May 12, 2015
    I like the above posts. But the OP was why?
    I know it burnt out and too much current was applied.
    As Dave said, red meat to charred meat.
    But in the electronics world, the led needs a certain forward voltage to EMIT. (light up).
    And current too. If that current exceeds the operating parameters of the led, it will die.

    Think of an incanescent light bulb. A 240v light bulb will work great.
    Plug that same light bulb into 500v. It will work for a second but die out rather quickly. It will also change colour before dieing. The led also is a diode and only works ONE way. The 'bulb' works both ways.
    Over current and over voltage kills a semiconductor.

    Martin
     
    davenn likes this.
  6. Robert Hill

    Robert Hill

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    12
    Mar 5, 2015
    My suggestion as to why it changed colour is that perhaps the plastic or resin or whatever encases the metal parts of the LED got burnt/melted as the inards of the diode got too hot and blew up. If you melt clear plastic it takes on a browny colour sometimes so maybe this is what is happening. Just a thought.
     
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