Electronics Led calculation question

Discussion in 'Modding' started by Monkey, 19 Jul 2004.

  1. Monkey

    Monkey What's a Dremel?

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    I was looking at the bit-tech calculator for the resistors needed for a led , now I know how to work out what resistor you need myself ,but how do you work out the power dissipated in the led and resistor. I know power is IxV ,but which figures are you suppose to use.

    I know I can just use the calculator to work it out , but I would like to know for myself.


    Thanks.
     
    Monkey, 19 Jul 2004
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  2. cpemma

    cpemma Ecky thump

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    For V, use the supply voltage less the led voltage.

    So a 2.1V red, running on 5V, about 15mA forward current wanted,

    R= (5-2.1)/.015 = 193.33, pick 200 ohms as nearest.

    Actual current will be (5-2.1)/200 = 14.5mA.

    Power = (5-2.1) x 14.5/1000 = 0.042W
     
    cpemma, 19 Jul 2004
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  3. Monkey

    Monkey What's a Dremel?

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    Thanks :).
     
    Monkey, 19 Jul 2004
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