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From: "Nucharin W. Jansen"
Subject: Re: Best way to power array of LEDs?
Date: Wed, 06 Nov 2002 05:19:42 +0700
Organization: C.S. Communications Co. Ltd.
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NNTP-Posting-Date: Tue, 5 Nov 2002 22:19:47 +0000 (UTC)
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What's happen when voltage drop across LEDs are not same ?
I have problem with white LEDs in series.
I can't control the current.
I have to adjust in real work one by one in each branch.
> "Jerry G." schrieb im Newsbeitrag
> > Each LED must have its own series resistor. Most of these LED's work
> > at about 30 to 40 ma with about 1.6 VDC across them. You should be able
> > to use a 320 ohm 1/2 watt resistor in series with each LED if these are
> > in the spec range that I used as an example.
> > LED's cannot be wired in parallel to each other being fed from one
> > resistor. They can not also be wired in series with each other.
> Nope, of cause they can be wired in series if the available voltage allows
> Check the datasheet for the typical forward voltage. Red leds have around
> 1.7V, yellow/green ones are 1.9-2.3V, blue/white ones even higher 3.2-3.8V.
> If you use just a resistor in series with each chain, you should calculate
> it for the max. supply voltage which I would suggest is 14.0V.
> Now if you put 6 red leds in series with 20mA current rating, you get
> 6*1.7V=10.2V; 14V-10.2V= 3.8V; 3.8V/20mA=190 ohms; take 180 or 200 ohms. The
> resistor can be a normal 1/4W 0207 type.
> ciao Ban
> electronic hardware designer
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