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Article #270Re: Best way to power array of LEDs?
From: Wouter van Ooijen (www.voti.nl)
Date: Fri, 04 Oct 2002 07:41
Date: Fri, 04 Oct 2002 07:41
30 lines
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2424 bytes
>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). > >What is the best method to power these from an intermittent (whenever I press >the brake pedal) power source? The crucial point is that when you put a resistor and N LEDs in series, the LEDs will take roughly a constant voltage so all voltage variation from your battery will be over the resistor, thus causing current variation. easy: separate resistor for each LED or maybe each 2 or 3 LEDs. constant current: Determine voltage drop over a LED, take N LEDs in series for a voltage drop of =< 9 V. Put in series with an LM317 in constant-current mode. for the brave: Put all LEDs in series, use a single switched power supply in constant-energy step-up mode to power the chain of LEDs. Wouter van Ooijen -- ------------------------------------ http://www.voti.nl PICmicro chips, programmers, consulting
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 112d1e,4ef4c9d4aea85e1f X-Google-Attributes: gid112d1e,public X-Google-Thread: 10d137,4ef4c9d4aea85e1f X-Google-Attributes: gid10d137,public X-Google-Thread: 1131b0,4ef4c9d4aea85e1f X-Google-Attributes: gid1131b0,public X-Google-Thread: 1118be,4ef4c9d4aea85e1f X-Google-Attributes: gid1118be,public X-Google-Thread: 103407,4ef4c9d4aea85e1f X-Google-Attributes: gid103407,public X-Google-ArrivalTime: 2002-10-04 00:41:16 PST Path: arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news.tele.dk!small.news.tele.dk!195.86.7.162!newsfeed.wirehub.nl!transit.news.xs4all.nl!not-for-mail From: wouter@voti.nl (Wouter van Ooijen (www.voti.nl)) Newsgroups: sci.electronics.components,sci.electronics.design,alt.engineering.electrical,aus.electronics,sci.electronics.repair Subject: Re: Best way to power array of LEDs? Date: Fri, 04 Oct 2002 07:41:30 GMT Organization: Van Ooijen Technische Informatica (www.voti.nl) Lines: 30 Message-ID: <3d9d452f.4128065@news.xs4all.nl> References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> NNTP-Posting-Host: a213-84-20-53.adsl.xs4all.nl X-Trace: news1.xs4all.nl 1033717274 29489 213.84.20.53 (4 Oct 2002 07:41:14 GMT) X-Complaints-To: abuse@xs4all.nl NNTP-Posting-Date: 4 Oct 2002 07:41:14 GMT X-Newsreader: Forte Free Agent 1.21/32.243