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Article #286Re: Best way to power array of LEDs?
From: Keith Wootten
Date: Fri, 04 Oct 2002 14:22
Date: Fri, 04 Oct 2002 14:22
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2897 bytes
In message <FbtkgUA9GZn9EwkP@jmwa.demon.co.uk>, John Woodgate <jmw@jmwa.demon.contraspam.yuk> writes >I read in sci.electronics.design that Keith Wootten ><keith.w@ntlworld.com> wrote (in <P0HAA5Jd3Un9EwWS@ntlworld.com>) about >'Best way to power array of LEDs?', on Fri, 4 Oct 2002: > >>You can mitigate this to a useful extent by using a small filament bulb >>instead of a resistor. The positive temperature coefficient of the bulb >>will help to keep the current variation reasonable as the supply voltage >>changes. The bulb should be selected to run at more or less normal >>brightness at maximum supply voltage while passing maximum LED current. > >A good idea IF you can find a suitable lamp. The lowest current lamps >readily available in UK (excluding 28 V ones) are 6 V 40 mA. You *could* >use one in series with two parallel strings of three LEDs. In fact the 50 LED array I use has only two connections, so must be ten parallel strings of 5 series LEDs. It's potted, but appears to be 50 individual 5mm LEDs. I suppose the Vf for each LED is reasonably similar. Mine draws about 100mA at 10V to about 200mA at 14V using the (two paralleled) bulbs. Cheers -- Keith Wootten
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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: 103407,4ef4c9d4aea85e1f X-Google-Attributes: gid103407,public X-Google-Thread: 1118be,4ef4c9d4aea85e1f X-Google-Attributes: gid1118be,public X-Google-Thread: 1131b0,4ef4c9d4aea85e1f X-Google-Attributes: gid1131b0,public X-Google-ArrivalTime: 2002-10-04 07:24:22 PST Path: arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!newsfeed.stanford.edu!cyclone.bc.net!newsfeed.media.kyoto-u.ac.jp!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!demon!newsfeed00.sul.t-online.de!newsfeed01.sul.t-online.de!t-online.de!newspeer1-gui.server.ntli.net!ntli.net!newsfep2-gui.POSTED!53ab2750!not-for-mail Message-ID: <QhSsxdkRQan9EwUs@ntlworld.com> From: Keith Wootten <keith.w@ntlworld.com> Newsgroups: sci.electronics.components,sci.electronics.design,alt.engineering.electrical,aus.electronics,sci.electronics.repair Subject: Re: Best way to power array of LEDs? References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <3d9d452f.4128065@news.xs4all.nl> <P0HAA5Jd3Un9EwWS@ntlworld.com> <FbtkgUA9GZn9EwkP@jmwa.demon.co.uk> Lines: 25 MIME-Version: 1.0 Content-Type: text/plain;charset=us-ascii;format=flowed User-Agent: Turnpike/6.02-U (<7r9OMDU2ooRJCQmjnYJxyjtHfm>) Date: Fri, 4 Oct 2002 15:22:09 +0100 NNTP-Posting-Host: 80.5.144.169 X-Complaints-To: abuse@ntlworld.com X-Trace: newsfep2-gui 1033741455 80.5.144.169 (Fri, 04 Oct 2002 15:24:15 BST) NNTP-Posting-Date: Fri, 04 Oct 2002 15:24:15 BST Organization: ntl Cablemodem News Service