a control circuit of a dc - dc converter that has a switching element , including an error amplifier that amplifies a difference between a reference voltage and a feedback voltage corresponding to an output voltage of the dc - dc converter , a voltage reduction comparator that outputs an interrupt signal when the feedback voltage is lower than a voltage reduction threshold that has a value lower than that of the reference voltage , and a pulse - width modulation signal generator circuit . the pwm signal generator circuit generates a pwm signal of a predetermined frequency based on the voltage difference when no interrupt signal is generated , or otherwise generates a switch drive signal to activate the switching element for a first period of time corresponding to the difference output by the error amplifier , and to deactivate the switching element for a second period of time after the first period of time has elapsed .