Soft start apparatus and method for dc-dc converter

A soft start device and method for a DC-DC converter are disclosed. The soft-start device for the DC-DC converter linearly raises the output voltage of the DC-DC converter by supplying a current in the linear mode and performs a switching operation according to the PWM duty in the switching mode to raise the output voltage to the target level , Determines whether to enter the switching mode from the linear mode, and controls the PWM duty based on the control signal in the switching mode. In addition, the device generates a control signal having an initial slope in a mode in which the mode is switched, thereby inducing the PWM duty to gradually increase in response to the slope at the beginning of the switching mode. In the switching mode, To limit the current of the DC-DC converter. Accordingly, it is possible to effectively prevent instantaneous inrush current from appearing when switching from the linear mode to the switching mode, and to achieve stable switching of the mode.