Re: 12 LED resistance circuit help

Brilla wrote:

> Hi, I want to make a simple LED circuit with 12 LEDs running off a
> nine volt battery. I've managed to dig up enough information about
> most things, so I know I'll have to wire them in parallel. But the
> resistance I should be using still confuses me.
> Should I have one (or more) resistors at the beginning of the circuit?
> Or one before each LED in the circuit?
>
> The LEDs I'm using have a 3.6v voltage drop, and they are supposed to
> get 20mA I beleive.
> So that's 12 LEDs off a 9v battery.

http://johnbokma.com/pet/scorpion/detection-using-uv-leds.html

9V, 3.6V drop ->

9V - ( 2 x 3.6 V ) = 1.8 V

so you want to have 1.8V over your resistor.

the 2 LEDs in series use 20mA ->

1.8V
----
20 mA = 90 Ohm


With 12 LEDs, you need 6 resistors. And the total current should be
around 6 x 20 mA = 120 mA.

Note that I did this calculation, later checked it with a voltage meter,
and yet already 2 exotic LEDs died on me. I think it's a bad badge.
(Unless someone can point out my errors).

--
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