Patent ID: 8334665

Claim:
A fan control system for controlling a fan to dissipate heat from an electronic device, comprising: a current detection circuit comprising a shunt resistor to receive current, a first terminal of the shunt resistor connected to the electronic device, a second terminal of the shunt resistor connected to the electronic device via a power source and being grounded; a signal amplification circuit comprising an operational amplifier, a first resistor, and a second resistor, wherein a non-inverting terminal of the operational amplifier is connected to the first terminal of the shunt resistor, and an inverting terminal of the operational amplifier is connected to the second terminal of the shunt resistor via the first resistor and connected to an output terminal of the operational amplifier via the second resistor; and a switch circuit comprising an npn transistor, a pnp transistor, a third resistor, a fourth resistor, a fifth resistor, and a sixth resistor, wherein the output terminal of the operational amplifier is grounded via the third resistor and the sixth resistor, a base of the npn transistor is connected to a node between the third resistor and the sixth resistor, an emitter of the npn transistor is grounded, a collector of the npn transistor is connected to a power supply via the fourth resistor and connected to a base of the pnp transistor via the fifth resistor, an emitter of the pnp transistor is connected to the power supply, and a collector of the pnp transistor is grounded via the fan.