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

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New Member
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:
555 PWM fan controller with rpm feedback

And then! ALAS! Just take a look at my circuit. I really worth it:
3-wire fan rpm controller with PWM pulses and rpm feedback

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


Well-Known Member
Most Helpful Member
It is a nice project but the BC328 transistor is connected upside-down.


New Member
Nice job!!


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.
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