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From: "Helmut Sennewald"
Subject: Re: Constant current source with low voltage drop
Date: Sun, 29 Sep 2002 07:06:20 +0200
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"markp" schrieb im Newsbeitrag
> Hi All,
> I need a constant current circuit adjustable from 0 to 150mA powered from
> 5V supply. This is to drive LEDs of an LCD backlight. The spec says a max
> 4.4V drop @ 150mA (2 LEDs in series?) so I've got to do this with a
> of 0.6V voltage drop. Any suggestions?
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:
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.
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