PWM 3 pin controller circuit?

[zryder]

Hello everyone.

I was doing some reading, and I noticed an excellent thread about controlling 4-pin PWM fans from a potentiometer, but I was wondering if anyone has a good circuit to do somewhat of the opposite. Take a 4-pin PWM input from the motherboard, and control via voltage a set of 3-pin fans, and let the rpm feedback return to the mobo.

Ideally this controller should be able to handle 6 gentile typhoon's.

Thanks for the help.

 

[Psycogeec]

it is more simple than it sounds.
the PWM signal would normally be the trigger for a mosfet gate in the fan itself.
get a fat mosfet , preferably one with good closed resistance properties at lower voltages, and trigger its gate instead, using the same signal

make sure that the mosfet is on the ground not the hot lead, that way the rpm feedback is still functional
make sure you get the right polarity of mosfet, because they are diodes also, so the direction and polarity is important
http://www.techpowerup.com/forums/showthread.php?t=115752

if the rpm feedback does not work still, then put a big fat capacitor or choke and capacitor curcuit setup on the other side of the mosfets power output, this will turn the chopped up power, into acting more like voltage controlling, and the feed from the rpm will not be effected by the pulsing so much.

a good low triggering mosfet , of the big fat size, or a good hexfet , would be able to drive many amps. the ammount of amps it could drive will be relative to the speed of the switching.
with really fast no fail switching, and a low resistance close on the mosfet, it can handle 30 amps easy.
if the switching is slow, or not FULLY switched, or only half switched a full sized mosfet item can still handle about 3-6amps.
so in the worst scenario, the big fat mosfet will still stay alive, making testing rather simple.
if you use tiny smd parts, they can also switch many amps, untill something goes wrong

In the curcuit shown, it is limited by the power plug on the board, the plugs on the board are limited in output , so you will want to power more direct.

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