Article View: sci.electronics.components
Article #236Re: Best way to power array of LEDs?
From: John Woodgate
Date: Mon, 07 Oct 2002 16:52
Date: Mon, 07 Oct 2002 16:52
31 lines
3006 bytes
3006 bytes
I read in sci.electronics.design that Lizard Blizzard <NOSPAM@rsccd.org> wrote (in <ans94t$moab$2@hades.csu.net>) about 'Best way to power array of LEDs?', on Mon, 7 Oct 2002: >John Woodgate wrote: >[snip] > >> A good guide is that the string should >> not take up more than half the lowest supply voltage. > >That will guarantee that the dissipation in the resistors exceeds the >LED dissipation. In other words, the circuit is not power efficient. In the automotive application, with 12 strings of 3 LEDs, we are talking about a TOTAL power of 12 V x 240 mA = 2.9 watt, using the extremely simple and cheap series resistor solution. Nine strings of 4 LEDs gives 2.2 W, which, considering the OP thought of a 9 x 4 arrangement, could be preferable. You could save 2 or 3 watts by going 0.1 mph slower. I doubt whether any of the other electronic solutions save as much. When doing engineering, do NOT suspend common sense. You do that only when doing quantum mechanics.(;-) The 'good guide' is about whether the crude 'voltage source and resistor' is an acceptable 'current source' or not. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL!
Technical Details
Message-ID:
<95qKYRBfvbo9EwZu@jmwa.demon.co.uk>Path:
arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!news.demon.co.uk!demon!jmwa.demon.co.uk!jmwReferences:
<0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <Rsan9.14070$qh1.1622310@news.ca.inter.net> <2Qan9.3129$cS4.107732@news2.tin.it> <6aa7QNAh$Yn9EwS7@jmwa.demon.co.uk> <ans94t$moab$2@hades.csu.net>Show Full Headers
Complete Article Headers
X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 112d1e,4ef4c9d4aea85e1f X-Google-Attributes: gid112d1e,public X-Google-Thread: 10d137,4ef4c9d4aea85e1f X-Google-Attributes: gid10d137,public X-Google-Thread: 1131b0,4ef4c9d4aea85e1f X-Google-Attributes: gid1131b0,public X-Google-Thread: 1118be,4ef4c9d4aea85e1f X-Google-Attributes: gid1118be,public X-Google-Thread: 103407,4ef4c9d4aea85e1f X-Google-Attributes: gid103407,public X-Google-ArrivalTime: 2002-10-07 11:23:58 PST Path: arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!news.demon.co.uk!demon!jmwa.demon.co.uk!jmw From: John Woodgate <jmw@jmwa.demon.contraspam.yuk> Newsgroups: sci.electronics.components,sci.electronics.design,alt.engineering.electrical,aus.electronics,sci.electronics.repair Subject: Re: Best way to power array of LEDs? Date: Mon, 7 Oct 2002 17:52:47 +0100 Organization: JMWA Electronics Consultancy Lines: 31 Message-ID: <95qKYRBfvbo9EwZu@jmwa.demon.co.uk> References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <Rsan9.14070$qh1.1622310@news.ca.inter.net> <2Qan9.3129$cS4.107732@news2.tin.it> <6aa7QNAh$Yn9EwS7@jmwa.demon.co.uk> <ans94t$moab$2@hades.csu.net> Reply-To: John Woodgate <jmw@jmwa.demon.co.uk> NNTP-Posting-Host: jmwa.demon.co.uk Mime-Version: 1.0 X-Trace: news.demon.co.uk 1034015037 19558 158.152.135.100 (7 Oct 2002 18:23:57 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Mon, 7 Oct 2002 18:23:57 +0000 (UTC) X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>