Help with simple LED circuit

Discussion in 'General Electronics Chat' started by noingwhat, Jul 23, 2010.

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  1. noingwhat

    Thread Starter Member

    Jul 23, 2010
    Hi! I am pretty new to circuitry (working on my first few projects). One of my projects was an LED flashlight hat. I had wired it up and everything, and it worked great. I used two 9v batteries in series with 5 LEDs in series, meaning each LED was recieving approx. 3.6v each. I have used the LEDs with 6v ea. using two 3v batteries wired in series, and it just made the LEDs really bright so I figured if I added another 9v battery meaning a total of 27v, that would be 5.4v per LED and it would just make it really bright. So I added it in and... It blew the LEDs. All five of them. Can anyone explain why, I do not understand why 5.4 blew the LEDs when 6v didn't.
  2. tom66

    Senior Member

    May 9, 2009
    5.4 volts is well above the rating of the LEDs (usually no more than 4 volts is acceptable for blue/white LEDs, and no more than 3 volts for others), what colour were your LEDs?

    For higher brightness I suggest the calculator:

    Use 25mA for the forward current, this will make your LEDs glow really bright.
  3. Wendy


    Mar 24, 2008
  4. bertus


    Apr 5, 2008

    Bill_Marsden is right, one thread is enough.
    Lets continue in the other thread.

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