A switching power supply may include: an inductor connected to an input voltage terminal; a first switch configured to form a first electrical path between the inductor and an output voltage terminal; a second switch configured to form a second electrical path between the inductor and a ground voltage terminal; a negative current sensor configured to sense an inductor current flowing through the first electrical path, and generate an over-current protection signal when the inductor current is sensed as a negative current equal to or more than a preset value; and a controller configured to enable a discontinuous conduction mode (DCM) when the over-current protection signal is generated, and turn off the first switch and turn on the second switch, in response to the enabled DCM.