Patent ID: 8164316

Claim:
A DC/DC converter comprising: a step-down control switch for receiving an input voltage; a first diode connected to the step-down control switch; a coil connected to both the step-down control switch and the first diode; a step-up control switch connected to the coil; a second diode connected to both the coil and the step-up control switch; a capacitor connected to the second diode; an error signal generating section connected to the capacitor to output an error signal, which represents the difference between the voltage across the terminals of the capacitor and a target voltage; a step-down PWM control section for generating a PWM control signal and controlling the step-down control switch upon receiving the error signal; a step-up PWM control section for generating a PWM control signal and controlling the step-up control switch upon receiving the error signal; a step-down PWM control switch connected between the step-down PWM control section and the step-down control switch; a step-up PWM control switch connected between the step-up PWM control section and the step-up control switch; and a MIX controlling section connected to both the step-down PWM control switch and the step-up PWM control switch and adapted to exclusively control the step-down control switch with the step-down PWM control section and control the step-up control switch with the step-up PWM control section by alternately switching between the step-down PWM control switch and the step-up PWM control switch in a state where the step-down PWM control section generates a step-down PWM control signal duty ratio at which voltage step-down effect of the step-down PWM control performed by the step-down control switch becomes the minimum and where the step-up PWM control section generates a step-up PWM control signal duty ratio at which voltage step-up effect of the step-up PWM control performed by the step-up control switch becomes the minimum.