resistanse of LED

Discussion in 'General Electronics Chat' started by alimech, Dec 29, 2013.

  1. alimech

    Thread Starter New Member

    Dec 29, 2013
    3
    0
    has LED resistor? if yes how much?
    i connect the 3v battery in led red 5mm and measure current.it would be 60mA.result is 3/60mA=47ohm.is that true?
     
  2. Ramussons

    Active Member

    May 3, 2013
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    92
    As far as I know, there is no "resistance" in LED's. Just like a diode, they have a voltage drop which varies with the current, upto a limit.

    In your experiment, the current is limited by the internal resistance of the cattery.

    Ramesh
     
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  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Here is a plot of the forward voltage V(f) [Red trace] of a typical Red LED as a function of current between 100uA and 30mA. Because LTSpice can do it, I also plotted V(f)/I(D1) [Green trace, units of Ohms]. What would you say the "resistance" of the LED is?
     
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  4. Austin Clark

    Member

    Dec 28, 2011
    409
    44
    I believe LED and diode resistance is roughly inversely proportional to voltage.
    Diodes has dynamic resistance. It's not constant.
    Try looking up incremental resistance.
     
  5. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    1,328
    LED's have little to no resistance. You forgot to take the forward voltage drop into account. Look at your LED's datasheet, find the forward voltage, subtract it from the actual (measured) battery voltage, and you get (roughly) the internal resistance of the LED. It should be very low.
     
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