Patent ID: 8890504

Claim:
A power adapter, comprising: a processing circuit converting mains power to another alternating current (AC) power or a direct current (DC) power; a first output outputting the converted AC power or DC power; a sense resistor connected between the processing circuit and the first output, for sampling a current flowing through the first output, and converting the sampled current to a sampled voltage; an amplifying circuit connected to the sense resistor for amplifying the sampled voltage to an amplified voltage; and a metallic oxide semiconductor field effect transistor (MOSFET), wherein a gate of the MOSFET is connected to the amplifying circuit to receive the amplified voltage, a drain of the MOSFET is connected to the first output through a first resistor, the drain of the MOSFET is further grounded through a second resistor, a source of the MOSFET is grounded, a node between the first and second resistors is connected to the processing circuit; wherein the amplifying circuit makes the MOSFET work at variable resistance region.