Does anyone know the output of the third pin (white wire) from a PC case fan? Is it a PWM or voltage or a square wave that is proportional to the RPM of the fan?
Do you mean that the motherboard outputs a square wave to control the fan? Or do you mean that the fan outputs a square wave to indicate speed of the fan?
I have designed a cpu fan driver IC,the output waveform is just a square wave ,it only indicate the speed of the fan,the cpu and motherboard don't control fan's speed by this pin.