A High-Power-Density Active-Clamp Converter with Integrated Planar Transformer

This paper proposes an active-clamp forward-flyback (ACFF) converter with an integrated planar transformer for wide-input voltage and high-output current applications, such as low-voltage direct-current (LDC) converters in electric vehicles. An integrated planar transformer that consists of a forward-flyback transformer, single primary winding, and efficient structure of secondary windings is adopted for the proposed converter, and since this transformer is implemented with a common four-layer printed circuit board (PCB) winding, a high power density and low cost of the proposed converter can be achieved. In addition, due to the low leakage inductance induced by the planar transformer, a reduced commutation period can be achieved, and it is possible to increase the switching frequency resulting in low volume of transformer. Although the integrated planar transformer has relatively high conduction loss, the active-clamp topology can significantly reduce the conduction loss on switches compared with widely used full-bridge (FB) converters because it only utilizes two switches and shows the low circulating current. As a result, the proposed converter with an integrated planar transformer has strengths in high power density and cost competitiveness without degraded efficiency, and it is a very attractive topology for LDC converters and other applications that require wide-input voltage and high-output current.