Switching power supply device, switching control device, and vehicle-mounted appliance

A switching control device configured to turn on and off

• a first switch configured such that a first terminal thereof is connectable to an application terminal for an input voltage, and that a second terminal thereof is connectable to a first terminal of an inductor,
• a second switch configured such that a first terminal thereof is connectable to the first terminal of the inductor and to the second terminal of the first switch, and that a second terminal thereof is connectable to an application terminal for a voltage lower than the input voltage, and
• a third switch being a GaN semiconductor element and configured such that a first terminal thereof is connectable to the first terminal of the inductor, to the second terminal of the first switch, and to the first terminal of the second switch, and that a second terminal thereof is connectable to a second terminal of the inductor,
• the switching control device comprising:
• an acquirer configured to acquire a detection result from a detector for detecting occurrence, or sign of occurrence, of an overshoot in an output voltage when the output voltage exceeds a predetermined constant voltage;
• and
• a suppressor configured to suppress an overshoot in the output voltage by controlling, according to the detection result acquired by the acquirer, states of the first switch, the second switch, and the third switch such that,
• in a first state where the first switch and the second switch are turned on and off complementarily at a fixed period, when a logic level of the detection result is switched, a transition is made to a second state where, while the first switch and the second switch are kept off, the third switch is turned on and off at the fixed period;
• in the second state, when the logic level of the detection result is switched, a transition is made to a third state where the first switch, the second switch, and the third switch are kept off;
• and
• in the third state, when, based on a periodic signal in which a pulse signal appears at the fixed period, the pulse signal appears, a transition is made to the first state.