The purpose of this paper is to present the transient response in the proposed digitally controlled dc-dc converter under the various changes. The digital PID control circuit has a delay time mainly due to the calculation and sampling. This delay time heavily affects the transient responses. In the proposed method, a twist is added to the PID control in order to achieve fast response. In addition, two kinds of low-cost A-D converters are used to realize low-cost design of the digital control circuit. As a result, the convergence time of proposed method is improved about 75% as compared with conventional method. Similarly, the undershoot of output voltage is improved about 45%. It is confirmed that the proposed method have superior transient response under the various changes.