Patent ID: 8432139

Claim:
A DC-DC converter, which is a synchronous step-down DC-DC converter, the DC-DC converter comprising: a high-side MOSFET as a main switching element, which is driven by using a bootstrap capacitor; a low-side MOSFET as a synchronous rectifier, wherein a series circuit of the high-side MOSFET and the low-side MOSFET is connected to a DC power supply; and a coil and a smoothing capacitor, which are serially connected between the drain and the source of the low-side MOSFET, wherein a direct current is output from the terminals of the smoothing capacitor by turning ON/OFF the high-side MOSFET and the low-side MOSFET complementarily; an overvoltage protection unit, which clamps an overvoltage when the direct current output voltage of the smoothing capacitor exceeds a predetermined value; an overcurrent interrupting unit, which interrupts an overcurrent that flows when the overvoltage protection unit clamps the overvoltage; and a protection circuit, wherein the protection circuit comprises: a differential-voltage detecting unit detecting the voltage of both ends of the bootstrap capacitor; and a control unit that, when the voltage detected by the differential-voltage detecting unit exceeds a predetermined value, turns OFF the low-side MOSFET and turns ON the high-side MOSFET.