Patent ID: 8680832

Claim:
A control circuit of a step-down DC-DC converter comprising: a main switching element which is coupled in series with a coil, which is coupled between an input terminal and an output terminal, wherein an input voltage is applied to the input terminal and an output voltage is output from the output terminal; a differential amplifier configured to output a differential signal between the output voltage and a reference voltage; a current sensing unit configured to detect a coil current flowing through the coil and to output a sense current; set circuit configured to add an offset current to the sense current; a current-to-voltage converting unit configured to convert a current to a voltage, wherein the current is obtained by adding the offset current to the sense current; a slope compensation circuit configured to output a slope signal which includes a first increase slope which is greater than a second increase slope based on the second increase slope of the voltage converted by the current-to-voltage converting unit; and a control circuit configured to compare the differential signal with the slope signal and to control the main switching element, wherein the offset circuit increases the offset current depending on an increase of the input voltage or a decrease of the output voltage, when the input voltage is more than the output voltage, and when the input voltage is not more than twice of the output voltage.