Patent ID: 8035326

Claim:
A controlling device of a fan, the controlling device is electrically connected with an alternating current power source and a motor of the fan for driving the motor to operate, the controlling device comprising: a magnetic detecting unit for detecting alternate magnetic poles states of the motor, wherein the magnetic detecting unit outputs a first voltage signal when the detected magnetic pole of the motor is N pole, and the magnetic detecting unit outputs a second voltage signal when the detected magnetic pole of the motor is S pole; a first switching unit electrically connected with the alternating current power source and the motor, respectively, the first switching unit being for receiving a positive phase voltage signal of the alternating current power source and outputting the positive phase voltage signal to the motor so as to drive the motor; a second switching unit electrically connected with the alternating current power source and the motor, respectively, the second switching unit being for receiving a negative phase voltage signal of the alternating current power source and outputting the negative phase voltage signal to the motor so as to drive the motor; and a controlling unit (IC 2 ) electrically connected with the magnetic detecting unit, the first switching unit and the second switching unit, respectively, the controlling unit being for receiving the first voltage signal and the second voltage signal and then controlling the first switching unit and the second switching unit according to the first voltage signal and the second voltage signal; wherein after the motor is started and when a frequency of a rotation rate of the motor is equivalent to a frequency of the alternating current power source, the controlling unit (IC 2 ) controls the motor to keep rotating at a constant rotation rate.