Re: Best way to power array of LEDs?

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#149

From: ehsjr
Date: Thu, 07 Nov 2002 05:03

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"Nucharin W. Jansen" wrote:
> 
> 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.
> 

Put simply, for most LED indicator circuits, all you have 
to do is limit the current.  You use the voltage spec
to figure how many LEDS can be series driven from the
source, and the LED string voltage drop, and the current 
spec to establish the limit.  You do not need to control
the voltage across a LED, only the current through it.

Unless you have some special requirements, you do
not need precision in either the voltage across, or
the current through an LED.  Just build a circuit
to limit for *maximum* current, using nominal LED 
voltage specs. 

If for some reason your circuit requires either precise 
voltage or precise current, than a simple resistor will not 
work for you, because the voltage drop across each LED is 
not identical to the spec.  And you can't precision
regulate the voltage across each LED in a series string,
nor can you precision regulate the current through each
LED in a parallel string.

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