# Electronics Quick LED Question

Discussion in 'Modding' started by cool_dude, 8 Apr 2007.

1. ### cool_dudeMinimodder

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26 Aug 2004
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Going to be supplying some leds with 5v....the led's require 3.2v - however i don t know what resistor i need to go for tech specs of led: Trying to do the working out...

V = I x R :
5 = 0.03 x R

So...

R = 5 / 0.03

=166.66

So does that mean for that LED to function at 3.2v using a 5v line i will need a 166 ohm resistor??
btw i want to wire them up parallel!

Help appriciated.

thanks,
c_d

Last edited: 8 Apr 2007
2. ### ConKbot of DoomMinimodder

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2 Jul 2003
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I wouldnt run it at 30 mA, as thats the maxium and you risk burning LEDs out quickly, especially if you get one with a lower Vf then normal. And the V that you want to use is the difference between the LEDs voltage and the power supply, not just the power supply.

so 5-3.0 = 2V

R = 2V / .020A = 100 ohms

For paralleling you would just give each LED its own resitor and hook it up the the 5v line.

However... what I would do is put 3 in series, giving you 9v for the LED string, and power them off the the 12v line.
so that would be:
(12v-9v)/.02 A = 150 ohms

Dont know what you're going to be using this in and if a series or parallel operation would work better for you. Either would work fine. Just dont be tempted to put 4 in series and put it across the 12v line with no resistors... you could get a few LEDs with a Vf of 2.8v. So the Vf of the string would be 11.2v then. Feeding that 12v would draw a lot more current then the LEDs are meant to handle , and it would end up frying.

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