Patent ID: 9593689
Date: 2017-03-14
CPC Classifications: F04D,H02P,Y02B

Claim:
1. A fan control circuit ( 2 ), applicable to a circuit board of an electronic device, wherein the electronic device includes a processing unit ( 3 ) and a fan ( 4 ) electrically connected to the processing unit ( 3 ) through the circuit board, the fan control circuit comprising: a filter circuit having an input end electrically connected to the processing unit for receiving a pulse-width modulation (PWM) voltage signal transmitted from the processing unit and converting the PWM voltage signal into a direct-current (DC) voltage signal, wherein magnitude of the DC voltage signal corresponds to duty cycle of the PWM voltage signal; an amplifier circuit having a positive input end separately connected to a first power supply unit and an output end of the filter circuit for receiving a static voltage signal transmitted from the first power supply unit, and the DC voltage signal transmitted from the filter circuit, respectively, wherein the amplifier circuit is to perform addition on the DC voltage signal and the static voltage signal, and then amplifies the combined signal to generate an amplified voltage signal at an output end of the amplifier circuit; a current expansion circuit having an input end connected to the output end of the amplifier circuit and an output end connected to the fan, wherein the current expansion circuit is configured to receive the amplified voltage signal transmitted from the amplifier circuit, perform a current expansion process on the amplified voltage signal, and thereby generate a driving voltage signal and a driving current signal at an output end of the current expansion circuit; and a feedback circuit having two ends respectively connected to a negative input end of the amplifier circuit and the output end of the current expansion circuit for delivering the driving voltage signal back to the negative input end of the amplifier circuit through the feedback circuit, enabling the magnitude of the driving voltage signal derived from the DC voltage signal by way of the amplifier circuit, the current expansion circuit, and the feedback circuit to be in proportion to the duty cycle of the PWM voltage signal and, in the meantime, enabling the driving voltage signal to be greater than or equal to a lowest driving voltage value of the fan even when the duty cycle of the PWM voltage signal is approaching to zero; wherein the first power supply unit keeps on providing the static voltage signal to the amplifier circuit even when the duty cycle of the PWM voltage signal is approaching to zero, the driving voltage signal output from the current expansion circuit is thus maintained to be greater than or equal to the lowest driving voltage value high enough for driving the fan into operation.