SWITCHING POWER SUPPLY DEVICE, SWITCHING CONTROL DEVICE, AND VEHICLE-MOUNTED APPLIANCE

A switching power supply device includes a first switch with a first terminal connectable to an application terminal for the input voltage and a second terminal connectable to the first terminal of an inductor; a second switch with a first terminal connectable to the first terminal of the inductor and a second terminal connectable to an application terminal for a voltage lower than the input voltage; a third switch being a GaN semiconductor element and connectable in parallel with the inductor; a detector detecting occurrence or a sign or occurrence of an overshoot in the output voltage; and a controller. The controller produces, after occurrence or a sign of occurrence of an overshoot in the output voltage is detected by the detector until settlement of the overshoot in the output voltage, a control state in which to keep the first and second switches off and the third switch on.