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Article #146Re: Best way to power array of LEDs?
From: Nucharin W. Jansen
Date: Wed, 06 Nov 2002 23:10
Date: Wed, 06 Nov 2002 23:10
30 lines
2731 bytes
2731 bytes
Typical Graph between V(f) and I(f) of each Ultra LEDs are not the same too. that made me very hard to calculate R drop and I think It can't calculate R on paper. I have to try adjust the POT in real world one by one with every strings. And don't swap LEDs between strings any more. > > Yes, I mean in series. > But two strings can not use the same R values. > So sad it very hards to calculate the current and R. > the forward voltage drop does not identical in each LED. > and it changes when current change too. > > ex: > > strings 1 : ( 12 volt - ( 3.453 + 3.6324 + 3.833 ) ) / 40 ohm = 27 mA > > Now I want 20 mA , How to calculate the resistor ? > Since forward voltage change when the current change too. > No, If you answer R = 40 * 0.027 / 0.020 = 54 ohm It is totally wrong. You can't get 20mA from R = 54 ohm. Because now at R = 54 ohm, the V(f) of 3 LEDs are change. headache.. We can't calculate R drop at the exact 20mA in the paper.
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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: 2002-11-06 15:15:03 PST Path: arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!snoopy.risq.qc.ca!newsfeed.news2me.com!newsfeed2.easynews.com!newsfeed1.easynews.com!easynews.com!easynews!uunet!dfw.uu.net!sac.uu.net!news.cscoms.com!not-for-mail From: "Nucharin W. Jansen" <tong@fanwap.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? Date: Thu, 07 Nov 2002 06:10:43 +0700 Organization: C.S. Communications Co. Ltd. Lines: 30 Message-ID: <3DC9A173.812F4764@fanwap.com> References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <Rsan9.14070$qh1.1622310@news.ca.inter.net> <2Qan9.3129$cS4.107732@news2.tin.it> <3DC843FE.4A25FFF3@fanwap.com> <aqblsd$10119$1@hades.csu.net> <3DC99AD4.2AB0FE52@fanwap.com> NNTP-Posting-Host: dial-12.ras-31.bkk.c.cscoms.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: news.cscoms.com 1036624249 52378 202.183.254.107 (6 Nov 2002 23:10:49 GMT) X-Complaints-To: abuse@cscoms.com NNTP-Posting-Date: Wed, 6 Nov 2002 23:10:49 +0000 (UTC) X-Mailer: Mozilla 4.8 [en] (Windows NT 5.0; U) X-Accept-Language: en