Recently I switched some case fans in my pc to find the horror that the new ones were even louder than the old ones. After some quick checks just by eyeing and monitoring on my pc I can confirm the new fans like to spin with the pc reporting about 1000 RPM whilst the old fans at best ran at around 600 RPM. These fans only have three pins so I though I could make some PWM controllers as a fun project, calculating the power drawn from the new fans would be in the range of about 2-2.5 watts per fan. So I'm thinking of using 5 watt components to drive it. However I came across no clear way to actually do this, for the tachometers to work I need straight DC into the fan.
I came across this circuit:
So would something like this work given I invert the signal just before sending it to the a power stage like the one shown in the upper quarter image? I think I remember PC fan PWM signals saying the fans should be off when the duty-cycle approaches 0 (until the built in shmitt trigger activates).
Would this work?