From: John Woodgate
Subject: Re: Best way to power array of LEDs?
Date: Mon, 7 Oct 2002 17:52:47 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 7 Oct 2002 18:23:57 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Lizard Blizzard
wrote (in ) about 'Best way to power array
of LEDs?', on Mon, 7 Oct 2002:
>John Woodgate wrote:
>> 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.
In the automotive application, with 12 strings of 3 LEDs, we are talking
about a TOTAL power of 12 V x 240 mA = 2.9 watt, using the extremely
simple and cheap series resistor solution. Nine strings of 4 LEDs gives
2.2 W, which, considering the OP thought of a 9 x 4 arrangement, could
You could save 2 or 3 watts by going 0.1 mph slower. I doubt whether any
of the other electronic solutions save as much.
When doing engineering, do NOT suspend common sense. You do that only
when doing quantum mechanics.(;-)
The 'good guide' is about whether the crude 'voltage source and
resistor' is an acceptable 'current source' or not.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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