A single-stage single-switch transformerless buck-buck converter with constant input power factor in the entire operational range

A single-stage single-switch (S4) converter integrating a buck-type power factor correction (PFC) cell and a buck-type dc-dc output cell is presented in this paper. The most attractive feature of the proposed S4 converter is that, its input power factor (PF) always keeps in constant even when the input voltage and the load change. Besides, the proposed converter also preserves the advantages of those existent S4 converters, such as the low voltage stress across the intermediate capacitor, low current stress of the switch and high step-down output voltage. These advantages make it cost-efficient and highly suitable for the low power and non-isolated applications. In this paper, the operational modes and circuit design are given, and a prototype is also built to show the validity of the analysis.