Analysis and performance comparison of a tooth wound brushless CPU cooling fan motor

Cooling fans for PC microprocessors often use two phase brushless motors to reduce electrical noise and to extend fan life. They are made with the winding on the inside of the motor (stator), and the magnet on the outside (rotor). This paper compares the static and dynamic performance of a tooth wound motor to results presented last year for a bobbin wound motor. The magnetic flux paths are described and a circuit model is developed for the tooth wound motor. From this model, startup and running torque are derived using the change in magnetic energy with rotor angle. A mechanical and electrical dynamic simulation is then used to investigate the torque, current and voltage as a function of time.