At 07:59 PM 6/12/01 -0700, Tim Thompson wrote:
>Hello,
>I'm attempting to have a PIC 16F877 in my project controll a small cooling
>fan. The fan is a 5V 0.09A dc brushless type, and is connected to a
>transistor which actualy drives the fan, it is connected like so:
>
>Transistor is a typical PNP 2N3906..
>Base through a 4.7K resistor to a PIC I/O pin,
>Emitter to +5,
>Collector to + side of fan, with a 4.7K resistor pulling to ground.
>(-) side of fan to ground, small diode between the +/- side to block any
>return voltages.

I would keep everything as you have it, except add a 2.2K resistor from
base to emitter.  That raises the turn on voltage of the transistor from
about 0.7V to about 2V.  Its easy to do and should fix your problem.

dwayne



Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 17 years of Engineering Innovation (1984 - 2001)

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