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From: "Spehro Pefhany"
Subject: Re: Constant current source with low voltage drop
User-Agent: tin/pre-1.4-19990216 ("Styrofoam") (UNIX) (Linux/2.2.14 (i586))
Date: Mon, 30 Sep 2002 18:12:46 GMT
NNTP-Posting-Date: Mon, 30 Sep 2002 14:12:46 EDT
The renowned markp wrote:
> I need a constant current circuit adjustable from 0 to 150mA powered from a
> 5V supply. This is to drive LEDs of an LCD backlight. The spec says a max of
> 4.4V drop @ 150mA (2 LEDs in series?) so I've got to do this with a maximum
> of 0.6V voltage drop. Any suggestions?
A resistor in series with a BJT driven by a PWM from the micro would be
minimal cost and would work well enough for many applications. If you
judge you want better control over the maximum current, make a 150mA
current sink and PWM *that*.
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