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Re: Calculating LED voltage drop

Discussion in 'Electronic Basics' started by John G, Aug 9, 2003.

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  1. John G

    John G Guest

    I don't think you can calculate the voltage drop of a LED.
    It depends on the construction and comes from the LED manufacturer's data
    sheet and is determined by the construction theniques. Super bright LEDS
    have a higher forward voltage than others.
    You only need to calculate a resisance to go with a particular LED and
    supply voltage.

    Try here
  2. bob cannetti

    bob cannetti Guest

    Does the "Voltage Drop" of an LED vary directly with the amount of
    current going thru it? If not, what are the common voltage drops for
    different LED's?
    thanks, bob.
  3. Well, yes, thats what the above equation means.

    Vd = vt.N.ln(Id/Is)

    If not, what are the common voltage drops for
    However, because of the log variation, it doesn't vary very much. If the
    current changes by a factor of 10:1, the voltage only changes by 60mv.
    Typical led voltages are 2-3 volts at their specified operating current.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  4. cpemma

    cpemma Guest

    You'll find Vf : If curves in the Kingbright datasheets,
    or at any other led maker's.

    A typical blue will drop about 3.4v @ 2.5mA, 3.7v @ 10mA and 4.2v @ 30mA.

    White and some pure green are in the same ballpark, red, orange, yellow,
    amber and other greens are around 1.8v @ 5mA up to 2.2v @30mA.

    It does vary with the exact chemistry, so check the datasheet for accuracy.
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