What is your goal?  From your circuit you are not showing the 620 ohm to +V 
where it should go even if it is a control voltage. Why did you not use just 
the PNP with a resistor and LED in the collector and the control voltage to 
a resistor in series with the base; as the voltage decreases the to the base 
resistor the PNP will forward bias and conduct harder and the LED will light 
brighter?

----- Original Message ----- 
From: "Spehro Pefhany" <speff@interlog.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Monday, August 10, 2009 12:15 AM
Subject: Re: [EE]Powering an LCD backlight


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