From: Kevin McMurtrie
Subject: Re: Best way to power array of LEDs?
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <2Qan9.3129$cS4.email@example.com> <3DC843FE.4A25FFF3@fanwap.com> <3DC99AD4.2AB0FE52@fanwap.com>
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Date: Wed, 06 Nov 2002 23:05:44 GMT
NNTP-Posting-Date: Wed, 06 Nov 2002 15:05:44 PST
In article <3DC99AD4.2AB0FE52@fanwap.com>,
"Nucharin W. Jansen" wrote:
>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.
>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.
Use a current mirror or current regulator.
Pick up a copy of "The Art of Electronics." It's what you need.
>Lizard Blizzard wrote:
>> Nucharin W. Jansen wrote:
>> > What's happen when voltage drop across LEDs are not same ?
>> > I have problem with white LEDs in series.
>> > I can't control the current.
>> > I have to adjust in real work one by one in each branch.
>> You say the LEDs are in series, so the current is identical in each one.
>> All you have to do is put a current limiting resistor in series with
>> those, and use a value that will give you the right current thru all.
>> If you made a mistake and meant parallel, then yes, you should not
>> connect LEDs in parallel without a resistor in series with each LED to
>> limit and equalize the current.
>> ----------------(from OED Mini-Dictionary)-----------------
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>> but ~the dog wagged its tail~ (no apostrophe).
>> ----------------(For the Apostrophe challenged)----------------
>> From a fully deputized officer of the Apostrophe Police!