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Subject: Re: Constant current source with low voltage drop
Date: Sun, 29 Sep 2002 13:02:16 +0100
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"Helmut Sennewald" wrote in message
> "markp" schrieb im Newsbeitrag
> > Hi All,
> > 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?
> Hello Mark,
> sometimes ago I designed this circuit.
> It uses a LDR(light dependant resistor) to control the backlght
> depending on the ambient light. If it is darker, the backlight
> intensity(current) is reduced.
> The description of the circuit is in the middle of this page:
> Chapter: 04.06.2002
> R1(P2) set the max. current. You wouldn't need P2, because you
> already know your maximum current.
> P3 has to be trimmed for minimum brightness.
> P1 shifts the control curve.
> P2 is for contrast and has nothing to do with the current source.
> Best Regards
Thanks! This is useful information.
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