My masterpiece: A PWM controller with rpm feedback, all from simple 3-wire fans!

[pcbheaven.com]

It was a long long ago when i start searching a solution for this problem. I Had 6 3-wire 120mm fans that i wanted to use for cooling purposes.
The requirements i had set was simple: I wanted to have full rpm control over the fan and have also rpm feedback. Well... not so simple as you will find out if you try it.

My first idea was a capacitor across the mosfet. I really did work, but the PWM pulses turned to be a switching power supply instead. That i did not like it. That is the first project:
**broken link removed**

And then! ALAS! Just take a look at my circuit. I really worth it:
**broken link removed**

Sorry for posting such an irrelevant subject but it took me many months to solve this problem and i just cannot hold myself!

 

[audioguru]

It is a nice project but the BC328 transistor is connected upside-down.

 

[fernando_g]

Nice job!!

But....

I also agree with Audioguru...Q2 is drawn and/or wired incorrectly. An PNP transistor must have its emitter more positive than its base and collector. Therefore it can't be connected to Vss.

 

[pcbheaven.com]

It's the 3rd time i copy a circuit wrong for crying out loud. Sorry. I used a NPN on the first place.