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Another LED question

Discussion in 'LEDs and Optoelectronics' started by Bounty, Apr 3, 2014.

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  1. Bounty


    Nov 25, 2013
    First of all I want to thank you for helping me with my previous LED problem. It works like a charm :)

    I have 3x 27ohm resistors left unused from last thing i 'built'. The questions is can I use these 3x resistors for another project?
    I would like to use only two blue LED diodes on any source.
    Can I somehow make a circuit that includes 2x blue LED diodes and up to 3x 27ohm resistors? Or maybe 3x diodes or anything similar..

    I tried calculating the values on the LED circuit calculators but I couldn't find anything to do with these three resistors.

    Thanks again.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The idea of finding a circuit just for using up available components sounds a bit unconventional.
    This won't work. Your choices of source are limited by the components at hand.

    Here's one example how you can use your components:
    [​IMG](Note: NSPW500S is only a placeholder for your LEDs)
    Each LED drops approx. 4V. Let's assume a current of 10mA throught each LED.
    10mA will drop 0.27V on each of R1 and R2. Current through R3 will be 2*10mA, therefore voltage drop across R3 is 0.54V.
    The total voltage across R3-R1-D1 (or R3-R2-D2, which is the same) will be
    4V (D1)+0.27V (R1)+0.54V (R3) = 4.81V.
    Therefore you could operate this circuit comfortably from 5V (e.g. USB power) or from 4.5V-6V with some variation in current.

    Attached Files:

    • bla.png
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      3.7 KB
  3. Bounty


    Nov 25, 2013
    Thanks,I will try this out as soon as I find time. :)
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