# connecting LEDs in series

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

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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

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Aug 31, 2014
Provide evidence of exactly what type of LED you are using.
You can make a BIG mistake.

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Jan 21, 2010

4. ### ramussons

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Jun 10, 2014
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.

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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