3pin (GND, 12V, tach) 12v FAN control using PWM I know there are fans out there that have a dedicated PWM input, but I like to know if I can PWM control a fan that does not have such a dedicated PWM input. So...
If I have a 3 pin 12v fan like the Noctua NF-A20 with connections:

GND
12 V
tach out (RPM measurement)

Can I control its speed by PWM on the 12V supply voltage (using a MOSFET most probably)?
Would the tach out still work?
Yes, and yes.
You have to modulate the +12V rather than GND because the output is referenced to ground. That means you need to use the classic N+P channel FET arrangement:



simulate this circuit &ndash; Schematic created using CircuitLab