A High Power Density 48V-12V DCX with 3-D PCB Winding Transformer

The design of the transformer is a key to achieve high efficiency and high power density for isolated dc-dc converters. Planar transformer has been used for its low profile. With the packaging technology development of the power devices, their footprints become smaller and smaller. However, restricted by the core loss density of high frequency soft ferrite materials, the reduction of the cross area of the transformer is insensible. Hence the transformer becomes the highest component in many high-density brick dc-dc converters, which restricts the improvement of power density. This paper proposes a 3-dimension (3D) PCB winding structure which surrounds the flat magnetic core, where the components can be mounted on the top and bottom layers of PCB windings. The transformer volume is reduced and the power density can be improved significantly. Finite element analysis is used to optimize the winding loss of the proposed transformer. A 1.6 MHz 48V-12V 300W DCX prototype with GaN device is built up to verify the 3D PCB winding concept.