Dc/Dc step-up converter and control method thereof

A DC/DC step-up converter and a control method thereof are provided to avoid an inflow current of an inductor while maintaining a soft start to increase an output voltage from zero. An input part has an inductor(L1) and a first switch(10) electrically connected to the inductor at both ends thereof. A controller has a second switch(11) electrically connected to one end of the input part. An output part is electrically connected to one end of the input part, and has a third switch(12) and a capacitor(Co) for outputting an output signal of the input part. A switch controller controls the first to third switches. When the output voltage of the output part is lower than the input voltage of the input part, the first switch is turned on, the second switch is turned off, and the third switch is switched.