connecting LEDs in series

[adel2014]

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

 

[Colin Mitchell]

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

 

[(*steve*)]

Please check out this, it will answer all of your questions and then some. Anything you don't understand, just ask

 

[ramussons]

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

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.

 

[PRIYADHARSHINI]

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

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

 

[adel2014]

thanks all , i appreciate your efforts