what resistor value for 2 indicator LEDS

mojoh · Post by **mojoh** » 15 Sep 2009, 04:42

i use a 2k2 resistor for a single 3mm indicator LED...if i wanted to have 2 indicator leds wired in series...what resistor value do i use???

cortezthekiller · Post by **cortezthekiller** » 19 Sep 2009, 05:47

I think anywhere from 1-2k should be reasonable for limiting the current to the leds

lolbou · Post by **lolbou** » 19 Sep 2009, 07:40

You need to know the nominal curent for your LEDs and the Forward voltage.

Example: I=20mA. Uf=2.2V.

You need the resistor to limit the current to 20mA (LEDs in series) and to drop the voltage by 9V-(2.2+2.2)=4.6V

This way, your LEDs voltages added to the resistor voltage would bring you up to 9V, and the nominal current is flowing in both LEDs...

Ohm's law says: R=U/I... 4.6/0.02=230 ohms.220 ohms would be brighter, 270 would be more reasonable?

Now you compute your own values...

edit: just remembered you mentionned you actual resistor value... Yes, i would go fo something like 1k3