I found this simple circuit using a Darlington pair: http://www.overclockers.com/forums/picture.php?albumid=395&pictureid=2336 As well as this one that uses a single mosfet and a cap (see page 2): http://pdfserv.maximintegrated.com/en/an/AN3530.pdf Which one would be a preferable circuit to take a 4pin signal from the motherboard to control 200mm fans (which are all 3-pin)? What would be the value of R1 in the darlington pair design? Also, to protect the fans, someone suggested using a Schottky diode. Would this be placed in parallel with the fan or in series? Finally, does anyone know the connector names for 3-pin and 4-pin (PWM) connectors used on the motherboards/fans? Thanks!