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From: "Nucharin W. Jansen"
Subject: Re: Best way to power array of LEDs?
Date: Thu, 07 Nov 2002 20:32:04 +0700
Organization: C.S. Communications Co. Ltd.
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <2Qan9.3129$cS4.email@example.com> <3DC843FE.4A25FFF3@fanwap.com> <3DC99AD4.2AB0FE52@fanwap.com>
NNTP-Posting-Date: Thu, 7 Nov 2002 13:32:06 +0000 (UTC)
To: Jim Yanik
X-Mailer: Mozilla 4.8 [en] (Windows NT 5.0; U)
Yes, I saw these at Maxim-ic.com
The brightness hard to matching.
Eyes can't matching them at 20% different.
It's ok. So people want to control the current
more than brightness matching.
For new modern LED ex: white or blue LED,
a normal resister can't calculate in paper.
We need to experiment directly in real circuit.
Because of forward voltage vary with current and
doesn't equal for every LEDs.
There are several ways to control the current.
- Resistor ( * hard to calculate the exact value for ULTRA BRIGHT LED )
- switching current regulator
- linear current regulator
- a light bulb
Jim Yanik wrote:
> The current-regulating LED driver IC's I've seen use one string of LED's
> with a resistor in series to monitor the current,it does not matter what
> the Vf is for each diode.Then additional strings of LED's can be added in
> parallel to the original string,with the same value R in series. I doubt
> the Vf of each diode varies so widely that it would make a significant
> difference in LED brightness. The LED's are not going to have matching
> brightness at equal current levels anyways.
> Jim Yanik,NRA member
> remove X to contact me
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