How do pwm controllers work?

[bob4933]

Are they adaptive or do they use potentiometers to control voltage?

 

[NiHaoMike]

They just output a square wave of varying duty cycle. It's actually a circuit inside the fan (low pass filter or DSP) that interprets the PWM and uses it to generate the correct drive signals for the motor. It's up to how the fan is designed as to how it interprets a given duty cycle, as in the RPM vs. duty cycle curve could be linear or nonlinear.

 

[m0r7if3r]

Are they adaptive or do they use potentiometers to control voltage?

It's not really as simple as that. You can have sensor-based (adaptive, as you put it) and manual adjustment on a PWM controller just as easily as a non-PWM controller. PWM is a way of controlling a fan without having to have a pot capable of handling the full wattage of the fan. It's also more efficient and results in less power loss through heat.