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From: John Fields
Organization: Austin Instruments,Inc.
X-Mailer: Mozilla 4.01 [en] (Win95; U)
Subject: Re: LCD backlight Dimmer circuit
NNTP-Posting-Date: Sun, 29 Sep 2002 13:21:40 CDT
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Date: Sun, 29 Sep 2002 18:21:40 GMT
Richard Soennichsen wrote:
> I need to dim an LCD backlight when an external 12V is applied as a signal.
> I have come up with many circuits that brighten the backlight but cannot
> find that "elegant" solution for dimming. The backlight can be considered
> an LED with a fixed resitor. The circuit has to effectively lower the
> voltage to the resistor or perhaps bypass the resistor and supply a lower
> voltage. Both low and high sides are available. Anyone? Thanks
Assuming your LED supply voltage is 12V and your 12V signal goes to 0V
(or at least a couple of volts below 12V) for full brightness,
12OFF>---[R]---B PNP |
Professional circuit designer
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