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connecting LEDs in series

Discussion in 'LEDs and Optoelectronics' started by adel2014, May 16, 2015.

  1. adel2014

    adel2014

    22
    1
    Dec 1, 2013
    hello every body , Greetings from Egypt , i am going to do a LEDs signs for cars using a SMD leds as showing , and i was asking Why i can not connect LEDs in series with out resistor , the supply is 12V and the number of LEDs in series is 6 , so every LED will take 2V - in the safe zone - , why i must put a resistor
     

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  2. Colin Mitchell

    Colin Mitchell

    1,418
    314
    Aug 31, 2014
    Provide evidence of exactly what type of LED you are using.
    You can make a BIG mistake.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,223
    2,696
    Jan 21, 2010
    Please check out this, it will answer all of your questions and then some. Anything you don't understand, just ask :)
     
    PRIYADHARSHINI likes this.
  4. ramussons

    ramussons

    343
    61
    Jun 10, 2014
    For your simplistic understanding:
    LED's don't behave like resistors - they don't follow i=v/r.

    Once they light up, the variation of current is very large for a small variation of voltage making it practically impossible to control the current and limit it to avoid a burnout.

    So you use a suitable resistor to limit the current or use a current source instead of a voltage source.
     
  5. PRIYADHARSHINI

    PRIYADHARSHINI

    137
    8
    Feb 6, 2014
    First You just check out your LED colour.each colour has different forward voltage(Vf).and you decide your forward current (If)...it depends upon your brightness level.
    for example R (curent limiting resistor) = (Vs - (Total Vf of all 6 series LED)/If
     
  6. adel2014

    adel2014

    22
    1
    Dec 1, 2013
    thanks all , i appreciate your efforts
     
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