From: Kevin McMurtrie
Subject: Re: Best way to power array of LEDs?
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <2Qan9.3129$cS4.email@example.com> <3DC843FE.4A25FFF3@fanwap.com> <3DC99AD4.2AB0FE52@fanwap.com> <3DC9A173.812F4764@fanwap.com> <3DC9B37F.453F9C41@fanwap.com>
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Date: Thu, 07 Nov 2002 09:59:21 GMT
NNTP-Posting-Date: Thu, 07 Nov 2002 01:59:21 PST
In article <3DC9B37F.453F9C41@fanwap.com>,
"Nucharin W. Jansen" wrote:
>He parallels all LEDs together without any resistor to
>constant voltage regulator.
>At last week, I thought the same as him but I plan to do with
>MAX757 ( DIP300 ) stepup IC from batt only 1 or 2 cells.
>But after read several articles here, I get confuse so much.
Some LEDs have a high internal resistance (~100 Ohms) so they can be
operated uniformly in parallel for high currents. It's not a good idea
to do this unless the internal resistance is a specified feature of the
For white light, I've rigged up panels that were strings of:
(-) ---- White --- White ---- Amber --- 47 Ohms --- (+12V)
They were fairly uniform in brightness for high currents but the string
was so picky about voltage that it was easier to put them all in series
and hack together a step-up switching power supply.