Controlling DC FAN with PWM

[ronv]

You can remove R3 and add a 12 volt zener diode to ground to prevent the gate voltage from going over 12 volts. Or you could move the bottom end of R3 to ground and the drain of the FET to Vout.
The 2N7002 is not a logic level FET. The gate threshold may be as high as 3 volts so it may not turn on real good. But it may well work as 3 volts is the high end of the spec.

 

[drkidd22]

Hey thanks got it going. So I get the same results with and without the optoiso. I tried with a few different DC fans and got the same results. It seems you get better control of the fans at lower frequencies 50-60hz pwm. I guess each fan might be different, but for the ones I have 50hz is best to control over different duty cycles