Patent ID: 7132809

Claim:
A fan controlling system applicable in an electronic system having a plurality of fans, the fan controlling system comprising: a signal generating module comprising a first signal generating module and a second signal generating module, both of which are used for generating pulse width modulation (PWM) signals and outputting the PWM signals to the fans of the electronic system according to control instructions output by the electronic system, so as to control the fans with the pulse width modulation signals; a phase-inverting module for inverting a second pulse width modulation signal outputted from the second signal generating module into a phase-inverted signal, which has a phase inverted to that of the second width modulation signal, and providing the phase-inverted signal to a second fan of the electronic system, so as to control the second fan with the phase-inverted signal; and at least a delay module for delaying a first pulse width modulation signal outputted from the first signal generating module and the phase-inverted signal generated by the phase-inverting module to generate a first delay signal and a second delay signal respectively, and outputting the first delay signal and the second delay signal respectively to a third fan and a fourth fan of the electronic system, so as to control the third fan and the fourth fan with the first delay signal and the second delay signal respectively.