Design and Implementation of a Transformerless Single-Stage Single-Switch Double-Buck Converter With Low DC-link Voltage, High Step-Down, and Constant Input Power Factor Features

This paper presents a new transformerless single-stage single-switch (S4) converter which integrates a buck-type power factor correction cell with a buck-type dc–dc output cell in a special way. The proposed converter preserves the advantages of existing transformerless S4 converters, such as the low voltage stress across the dc-link capacitor, low current stress of the switch, and high step-down input-to-output voltage. Moreover, the proposed converter provides a new attractive feature, i.e., its input power factor always keeps constant even when the line- and load-conditions vary. These characteristics make the proposed converter cost-efficient, easy-to-design, and suitable for the low-power and nonisolated applications. The principle and analysis of the proposed converter are presented in this paper, and a design example is also given to show the validity of analysis.