A LC filter can be added to the input of the conventional buck converter to make the converter operate in discontinuous capacitor voltage mode. In this mode, the converter obtains the inherent power factor correction. Besides, both the input and output current will be continuous. This makes it possible for the converter operating at a high power level range. The input current will follow the input voltage automatically by a simple constant duty cycle control. This paper presents a detailed operation analysis of the converter operating in discontinuous capacitor voltage mode. And a 36 V/100 W prototype was built to verify the theoretical results.