Take a look at this: http://www.nanoxia-europe.com/index.php ... 15&lang=en
Many users are looking for a way to benefit from the possibilities of the 4-Pin-PWM-Controller even with conventional 3-Pin fans, e.g. using a 3-pin CPU fan on PWM-enabled mainboards. The Developers at Nanoxia tackled this dilemma and came up with a solution: With the brand new PWMX Controller it is now possible to control all 3-pin fans via PWM.
The Nanoxia controller chip detects the connected fan and generates fitting PWM characteristics. This way, every fan can be accessed perfectly by a PWM-enabled mainboard. Contrary to pure PWM solutions, the PWMX Controller allows to regulate the supply voltage of the fan, thereby offering a higher level of adjustment, e.g. reducing the maximum rotation speed of the fan while still react to current CPU load.
Dimensions: 3,2 x 1,2 x 1,3 cm
Control Range (Voltage): 5V-12V
Connector Input: 4 PIN PWM Connector (to mainboard)
Connector Output: 3 PIN Fan Connector
I think it's very interesting! It seems like you can control 3-pin fans from 4-pin PWM connectors, translating the PWM signal to different voltages.