From: John Woodgate
Subject: Re: Best way to power array of LEDs?
Date: Fri, 4 Oct 2002 13:56:01 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Fri, 4 Oct 2002 14:08:38 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Ban wrote
(in <2Qan9.3129$cS4.firstname.lastname@example.org>) about 'Best way to power array
of LEDs?', on Fri, 4 Oct 2002:
>Now if you put 6 red leds in series with 20mA current rating, you get
>6*1.7V=10.2V; 14V-10.2V= 3.8V; 3.8V/20mA=190 ohms; take 180 or 200 ohms. The
>resistor can be a normal 1/4W 0207 type.
But the current drops to around 10 mA when the battery voltage is 12 V,
which may or may not matter in terms of reduced brightness. With a
string of 3 LEDs in series, and 470 ohms, the current at 14 V is 19 mA
and at 12 V it is around 15 mA. A good guide is that the string should
not take up more than half the lowest supply voltage.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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