Embodiments of the present invention relate to a switch control circuit, a switch control method, and a power supply device using the same.Embodiments generate a reference signal according to a full-wave rectification voltage and control a switching operation of a power switch according to a comparing result of a sense voltage corresponding to a current flowing to the power switch and the reference voltage. Embodiments determine whether a line is opened between a first output terminal and a second output terminal of the power supply device using the sense voltage. When the line is opened, Embodiments turn off the protection switch.