I would like to know if anybody has experience with controlling the speed of a PC power supply fan.
I know that effectively there is a controller in the fan to let the brushless moter rotate.
I can reduce the turning speed of the fan by lowering the power supply, I do this normally with a lab power supply.
I want to use an AVR to control the turning speed depending on a measured temperature.
Now I can do this in 2 ways. either I use a big fat NFET that I set to better or worst conducting, or I use a lighter FEt that I set to switching mode and as such I use a PWM signal to adjust the motor speed.
In both cases I use PWM, but in one condition I use the FET as a resistor and thus lower the voltage over the motor and in the other case I switch ON and OFF the FET and reduce the average voltage over the motor.
The big difference is the amount of power dissipated both in the FET and the system.
does anybody have experience on this?