need help figuring out bias resistors on a tip141

[fawnserelli]

I am building a pwm circuit for a 3 pin computer fan using a tip141 transistor to do the switching. i want control over fan speed using a program which alters the pwm frequency %. the fan is a 1 amp fan.

 

[MikeMl]

Welcome Fawn,

So if the TIP141 is used as a PWM switch, why do you need "bias"?

Are you asking how to drive the base of the TIP141 from a micro-controller port pin?

Are you going to use the speed monitor output in your application? If so, you will need a high side switch which requires a PNP version of the Darlinton, not the NPN version.

You might want to **broken link removed**