Thanks everyone for your help, it apears adding a base-emitter resistor did the trick. Thanks again everyone for your help. Thanks, Tim Thompson At 11:03 PM 6/12/2007 -0700, you wrote: >Tim, > >I wopuld put a 10K ohm resistor from base to Emitter, and change the 4.7K >base resistor to 1K. The 10K will pull the base high unless it's driven >low. >This will tend to hold the transistor off. When the PIC pin is taken low, >the >1K resistor will allow 5 mA of base current (Approx) which should be more >than enough to drive the transistor on. As an aside, what is the HFE of the >transistor you are using. Is it greater than 100? My guess is around 150 >to 200. If this is so, then the resistor values I suggest should work fine. >Let us know if this helps you out. > > Regards, > > Jim >----- Original Message ----- >From: Tim Thompson >To: >Sent: Tuesday, June 12, 2001 7:59 PM >Subject: [PIC]: Problems using PIC to controll small fan > > >> 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. >> >> By setting this I/O pin (PORTE,2) low, the fan comes on as expected. >> However i cannot turn the fan off by setting the port high! If i jumper +5 >> directly to the i/o pin manualy the fan goes off..but it dosnt apear the >> pic can source enough to turn it off...what am I doing wrong? Probly >> something stupid..anyway >> >> Thanks in advance, >> Tim Thompson >> >> >> >> - >> Remember, 'kill' doesn't kill processes, users kill processes. >> >> -- >> http://www.piclist.com hint: The list server can filter out subtopics >> (like ads or off topics) for you. See http://www.piclist.com/#topics >> >> >> > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. > > > > - Remember, 'kill' doesn't kill processes, users kill processes. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.