Patent ID: 7151349

Claim:
A method of synchronizing a pulsed drive signal applied to a DC fan motor to the TACH output of the motor, the motor including a rotor that rotates in a path defined by a plurality of magnetic poles, the method comprising: a) defining an ideal TACH output for a specific rotation speed of the rotor of the DC fan, said ideal TACH output being related to the ideal rate passing of a magnetic pole of the fan by the rotor, b) monitoring the actual TACH output of the DC fan, the TACH output indicating the passing of the magnetic poles of the fan by the rotor, c) comparing the monitored TACH output to the ideal TACH output, and d) changing the period of the drive signal if the monitored TACH output does not match the ideal TACH output such that the period of the drive signal matches the time taken for the fan to rotate through one magnetic pole of the fan.