Patent ID: 8248016

Claim:
A fan circuit for driving a fan, the fan circuit comprising: a control chip to output a discrete pulse width modulation (PWM) signal changing with temperature; an input circuit connected to the control chip, to convert the PWM signal into a continual voltage signal; an amplifier circuit connected between the input circuit and the fan, to amplify the voltage signal and output a control signal, wherein the amplifier circuit comprises an amplifier, an inverting input terminal of the amplifier is connected to the input circuit via a first resistor, and is also connected to an anode of the fan via a second resistor, a non-inverting input terminal of the amplifier is grounded via a third resistor, and is also connected to a control circuit via a fourth resistor, and the ratio of resistances of the second resistor to the third resistor is equal to the ratio of resistances of the fourth resistor to the first resistor; and said control circuit is connected to the amplifier circuit, wherein when the control signal is less than a threshold voltage, the control circuit is turned on and the fan receives current which is less than preset current, when the control signal is greater than the threshold voltage, the control circuit is turned off and the fan receives current which is greater than the preset current.