Wiring Schematic Diagram

The following project is a PWM fan control, It is very easy to be built and it can efficiently control all DC fans to rpm as low as 450 rpm (the lowest limit has to do with the fan type and manufacturer). It uses ONLY one 555 timer and a few other components, and it can be powered also directly from the PC power supply, from the 12 Volts line.

The 555 will create a series of PWM pulses and will be driven directly to the gate of the MOSFET. The MOSFET is chosen to be big enough to carry enough loads, up to 9.2 amperes. You can choose a MOSFET according to your needs.

The MOSFET will generate enough power so that the motor will start revolving. The capacitor across the MOSFET is the solution to the'kicking sound'. The MOSFET will send to the motor pulses according to the pulses generated from the 555. If you remove the capacitor, you will definitely hear this annoying sound. The capacitor will smooth the voltage across the motor and therefore the power driven to it will be smooth, avoiding the torque kick