is there a simple explanation with 4 pin pwm pc fans, vs using 2 pin pc fans on pwm? do the 4 pin pwm have a built in motor controller?
All PC fans have a built-in brushless DC motor controller. The 4-wire ones are designed to be speed-controlled and will generally go down to 30% of full speed or lower. 2- and 3-wire fans may not be controllable over as large a range.
There are a couple of further advantages of 4-wire fans:
If you don't need to turn them off completely, then you don't need to use a transistor to drive them;
The tacho output still works properly even when you apply PWM.
thank you this is what i needed as i am looking to run a fan at a fairly low speed. i did do this with a 3 pin (not using the sensor wire) but it was buzzing quite a bit. hope i get less of that with the 4 pin.