Embodiment relates to a switch control circuit, a switch control method, and a power supply using the switch control circuit. The power supply supplies power to a load using an input voltage. The switch control circuit controls a switching operation of the power switch that controls the power supply. The switch control circuit detects a duty of the power switch using a signal for controlling the switching operation of the power switch, detects the load using the feedback voltage, and determines a short-circuit of the sense resistor according to the detected duty and the detected load.