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LEDs Playing Nice Together

Discussion in 'LEDs and Optoelectronics' started by Raven Luni, Jan 13, 2012.

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  1. Raven Luni

    Raven Luni

    Oct 15, 2011
    Bit of a noob question but I was testing some LEDs the lazy way just by touching them parallel to LEDs in an existing circuit. Some didnt work this way and would only light on their own (specifically superbright green 3mm). Is this something to do with different voltage drops?

    (they explode really well too :D - decided to risk touching one to the 9v supply just for an instant but forgot about the 4700uF capacitor connected there - hehe)
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    If two LEDs have a significantly different Vf, only the one with the lower Vf will light up.

    If the Vf (at some nominal current) is only slightly different, the one with the lower Vf will get more current since Vf is slightly dependant on current (obviously the actual Vf will be identical if in parallel).

    Vf is typically Vf @ some current and temperature.
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