From: Jim Thompson
Subject: Re: Constant current source with low voltage drop
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Date: Tue, 01 Oct 2002 17:59:05 GMT
NNTP-Posting-Date: Tue, 01 Oct 2002 13:59:05 EDT
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On Mon, 30 Sep 2002 18:12:46 GMT,
"Spehro Pefhany" ,
In Newsgroup: sci.electronics.design,
Entitled: "Re: Constant current source with low voltage drop",
Wrote the following:
|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*.
I have posted a linear approach on A.B.S.E at
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
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