Patent ID: 8013585

Claim:
A DC-DC converter comprising: a first switching element connected to a high potential side of an input power source; a second switching element connected in series with the first switching element, and connected to a low potential side of the input power source; a filter circuit connected to a connection point between the first switching element and the second switching element, and including an inductor and a smoothing capacitor that feed a smoothed output voltage to a load circuit; a voltage detection circuit that detects an output voltage of the load circuit so as to output a negative feedback signal; a control circuit that compares the negative feedback signal and a first reference voltage and amplifies a difference therebetween, so as to output first and second control signals for switching the first and second switching elements respectively; and driver circuits that alternately control the first switching element and the second switching element to be ON and OFF respectively in accordance with the first and second control signals; the driver circuits including: an overcurrent detection circuit configured to detect a magnitude of an inductor current that flows through the inductor during an ON period of the second switching element by comparing a voltage drop across the second switching element with a second reference voltage, and configured to decide whether or not the magnitude of the inductor current has decreased to a predetermined magnitude; and a timing alteration circuit configured to alter timing of the first control signal so as to extend an OFF period of the first switching element until it is decided by said overcurrent detection means that the inductor current has decreased to the predetermined magnitude, wherein said overcurrent detection circuit comprises: a level shift circuit that adds a predetermined voltage to a drain-source voltage of the second switching element, so as to output a resulting voltage; a reset circuit that fixes an output signal from said level shift circuit, to a predetermined value during the OFF period of the second switching element; and a decision circuit that decides if an output signal voltage from said level shift circuit has reached the second reference voltage during the ON period of the second switching element.