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Subject: Re: Constant current source with low voltage drop
Date: Mon, 30 Sep 2002 22:10:54 +0100
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"Spehro Pefhany" wrote in message
> The renowned markp wrote:
> > I need a constant current circuit adjustable from 0 to 150mA powered
> > 5V supply. This is to drive LEDs of an LCD backlight. The spec says a
> > 4.4V drop @ 150mA (2 LEDs in series?) so I've got to do this with a
> > 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*.
Indeed. I have decided now that this is the way to do it, except I'm using a
MOSFET instead of a BJT and a pot to set max current. This also leads itself
to CPU control by passing the PWM signal through a PLD.
Thanks for all wo responded!
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