Patent ID: 7826722

Claim:
A driving apparatus for a fan motor, electrically connected between a pulse width modulation (PWM) signal generator and a controller, comprising: a converter electrically connected to the PWM signal generator and outputting a first reference voltage according to a duty cycle of a PWM signal generated by the PWM signal generator, wherein the converter is a charging and discharging circuit comprising a first and second switching device, a third resistor and a capacitor, each of the first and second switching devices being a metal-oxide-semiconductor (MOS) device, and wherein the first switching device has a gate electrically connected to the PWM signal generator, a drain directly electrically connected to a gate of the second switching device, and a source electrically connected to a ground terminal; a reference voltage generator electrically connected to an external power source, and generating a second reference voltage according to the external power source; and a comparator having a first and second input terminal and an output terminal; wherein the first input terminal is electrically connected to the converter and receives the first reference voltage, the second input terminal is electrically connected to the reference voltage generator and receives the second reference voltage, and the output terminal is electrically connected to the controller; when the first reference voltage is greater than the second reference voltage, a driving signal is output from the output terminal to the controller so as to control a rotation speed of the fan motor, and when the first reference voltage is not greater than the second reference voltage, the controller drives the fan motor at a fixed low speed according to a predetermined low speed setting.