From: Lizard Blizzard
Subject: Re: Best way to power array of LEDs?
Date: Fri, 04 Oct 2002 17:19:23 -0700
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <firstname.lastname@example.org> <email@example.com>
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> In the auto situation, the simplest mitigation is to feed the
> resistor/LED chain thru an LM317 configured as a constant current
> source. Just the IC and one resistor added, and no voltage variation
The LM317 has a minimum current which may be greater than a single LED
can handle. It will work good for a hundred mA or more. But probably
the biggest objection to using the LM317 is that they cost a buck or two
each, so if you use one for each series string of LEDs, you can end up
with more cost for the regulator than the LEDs.
If you're going to spend the money on an LM317, change it to an LM334,
which is a true current regulator. Even cheaper might be a JFET with
the gate connected to the source. Problem with that is that the JFETs
have such a wide range of Idss that you might pick a dozen of them and
they might all have a wide variation in current.
Here's a URL for a LED current regulator using the grain of wheat 1.5V
25 mA bulbs from Rat Shack. I don't particularly like using lamps for
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