Patent ID: 7646162

Claim:
A control circuit for fan operating comprising: a drive operating circuit at least having a voltage source, a drive IC, a Hall IC and a motor coil winding, wherein the drive IC is connected with the voltage source, the Hall IC and the motor coil winding are connected with the drive IC; a potential modulating circuit connected with the drive IC of the drive operating circuit having a modulating signal source, the modulating signal source providing a PWM signal with a duty cycle; a comparator having an input end and an output end, wherein the input end is connected with the potential modulating circuit, potential state of the output end is determined in accordance with the duty cycle of the PWM signal; and a switch circuit connected with the drive IC of the drive operating circuit and the output end of the comparator, wherein operating state of the drive IC of the drive operating circuit is determined in accordance with potential state of the output end; wherein the potential modulating circuit further has a first transistor, a voltage-dividing unit and a reference unit, the first transistor is connected with the modulating signal source and the voltage-dividing unit, the voltage-dividing unit and the reference unit are connected with the input end of the comparator; and wherein the drive IC has a level control pin connected with the voltage-dividing unit of the potential modulating circuit and a capacitance switch pin connected with the switch circuit.