(****, 3rd time writing the reply x.x first one didnt appear after 3 days, and the 2nd time firefox froze)
summarising 'cause it was a long post and now i'm lazy to write it up again.....
non-pwm = 2wires, 12v and ground, and maybe the sensor, aka without the fourth wire (PWM signal)
the standar fans are uselles to me, because i have my machine overclocked(X6 @3.5GHz, 4HHDs, HD 6950 that barely fit inside the case, etc) so it gets hot.
the fans that i have now are some sunon maglev 3100RPM 0.45A, without pwm, nor sensor.... and i wanted to use some of those high current transistors to control them because runing always at maximum speed they get a little too much anoying ^^
but there's also this fan that is a beast, 6400RPM, 3A. and i wanted to be able to use those too, so thats way i need it to be able to deliver that much current.
https://db.sanyodenki.co.jp/product_db_e/coolingfan/dcfan/dc_fan_detail.php?master_id=1637
I'm also thinking about making the step up go up to 30V cause i saw some fans taking 30V without burning....maybe not 30V for 24/7 but 20 could go without problem...
making a cheap 7 bucks 1200 rpm at 12V go 2000 rpm at 20 looks like a good idea. and the 3100 go 5150 (+66%) even better.
EDIT:
thanks Ron, circuit helped me (who would have guesed that the load had to be in the drain side for it to work....) but the output signal is inverted...."NOT" function there