Patent ID: 7135844

Claim:
A control circuit for a DC/DC converter comprising main switching means, sub switching means, and a reactor and adapted to convert a DC input voltage to a predetermined DC output voltage, the control circuit comprising: clock signal generation means for generating a clock signal in a blank period in which both the main switching means and the sub switching means are off; a comparator for comparing a predetermined reference voltage higher than the ground potential but lower than the DC output voltage of the DC/DC converter, and a voltage at a connection point at which the main switching means and the sub switching means are connected together, and for outputting a comparison signal indicating a relation of magnitude between the reference voltage and the voltage at the connection point; and operation mode switching means operating such that when the voltage at the connection point during the blank period which is latched in response to the clock signal is not higher than the reference voltage, control is determined to be performed in a regular mode, whereby the main switching means and the sub switching means are alternately turned on and off; and when the voltage at the connection point during the blank period is higher than the reference voltage, the control is determined to be performed in a non-regular mode, whereby only the main switching means is turned on and off at a predetermined duty, with the sub switching means being maintained off.