Re: Best way to power array of LEDs?

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#237

From: Kevin McMurtrie
Date: Mon, 07 Oct 2002 19:09

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In article <ans94t$moab$2@hades.csu.net>,
 Lizard Blizzard <NOSPAM@rsccd.org> wrote:

>John Woodgate wrote:
>[snip]
>
>> A good guide is that the string should
>> not take up more than half the lowest supply voltage.
>
>That will guarantee that the dissipation in the resistors exceeds the 
>LED dissipation.  In other words, the circuit is not power efficient.

But this is for automotive power.

Let's say you use 10V of LEDs.  Now the voltage drop will be between 
1.5V and 6V with a normal of 4.5V.  You can't maintain good current 
regulation with a simple resistor.  For 225 Ohms: 6mA min, 20mA normal, 
27mA max.

If you use 6V of LEDs, the voltage drop will be between 5.5V and 10V 
with a normal of 8.5V.  A resistor is good enough here.  For 425 Ohms: 
13mA min, 20mA normal, 24mA max.

I imagine there's at least 4 amps to spare on the brake light line.

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From: Kevin McMurtrie <mcmurtri@sonic.net>
Newsgroups: sci.electronics.components,sci.electronics.design,alt.engineering.electrical,aus.electronics
Subject: Re: Best way to power array of LEDs?
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