From: John Woodgate
Subject: Re: Best way to power array of LEDs?
Date: Fri, 4 Oct 2002 09:50:34 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Fri, 4 Oct 2002 10:50:54 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Tilmann Reh
wrote (in <3D9D32DE.firstname.lastname@example.org>)
about 'Best way to power array of LEDs?', on Fri, 4 Oct 2002:
>> Have assembled an array of LEDs for use as a 3rd brake light in my car,
>> configured as 4 rows of 9 jumbo LEDs, as of yet unwired. Of course the power
>> supply will be 12 volts nominal (13.8 volts, maximum).
>> My options, as I see them, are:
>> 1) Wire individual resistors to each LED based on its operating current
>> 2) Wire each row in parallel and connect one resistor based on operating
>> current for 9 LEDs
>> 3) Install voltage regulator to output voltage (ie, 1.3 volts?) to operate
>> all LEDs in parallel.
>> What is the best method to power these from an intermittent (whenever I press
>> the brake pedal) power source?
>Better use many LEDs in series to avoid unnecessary power loss.
>With 12V supply, you can use about 5 LEDs in series and a smaller
>resistor for each chain. These chains are then connected in parallel.
There was a VERY long thread on this a few weeks ago on s.e.d. There
were a lot of reasons dredged up showing that ALL forms of connection
are undesirable (;-).
In your case, the 'engineering solution' is to run groups of 3 LEDs in
series from one dropping resistor. If you want to run at 20 mA (lower if
possible), use 470 ohms. A half-watt resistor is OK, but you can use a
higher rating if you want to.
Don't even try to run them from a regulated voltage source. LEDs need a
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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