From: Lizard Blizzard
Subject: Re: Best way to power array of LEDs?
Date: Thu, 07 Nov 2002 12:45:49 -0800
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <2Qan9.3129$cS4.firstname.lastname@example.org> <3DC843FE.4A25FFF3@fanwap.com> <3DC99AD4.2AB0FE52@fanwap.com>
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John Woodgate wrote:
> [snip] Furthermore, 1.09 V is not really enough voltage to
> operate a simple electronic constant-current circuit.
Not true. Here's one that's not that complicated and runs a 3.5V white
or blue LED off 4 AA Ni-Cds of from 3.8 to 5.6V depending on their state
of charge. As he says, it requires only 0.2V more than the LEDs. I
modified the circuit to use a single LED, and changed the power FET to a
2N4401, plus some other circuit resistance changes. I get substantially
the same results. Regulation is within about 6 percent; not great but
What I'm trying to do right now is boost the current enough to drive
four or more output transistors in parallel for four or more LEDs. I
may go back to the really inexpensive MOSFET 2N7000 for the output
device, since they draw zero gate current, so I can drive dozens of them
as in the original circuit at this URL. The only disadvantage is that
neither lead of the LED is grounded.
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