A low-profile power converter using printed-circuit board (PCB) power transformer with ferrite polymer composite

A new design of low-cost and low-profile power transformer is presented in this paper. The manufacturing cost of a power transformer can be reduced using the proposed printed-circuit board (PCB) transformer. The transformer windings are etched on the opposite sides of a double-sided PCB. Self-adhesive ferrite polymer composite (FPC) sheets are stuck on the two PCB surfaces to shield the magnetic flux induced from the transformer windings. The PCB transformer does not require manual winding and bobbin. A power converter prototype employing the PCB transformer has been implemented. The technique of choosing the optimum switching frequency of the power converter using the PCB transformer is addressed in this paper. The maximum power delivered from the prototype is 94 W. The maximum efficiency of the power converter is 83.5%.

I. Introduction

The continuous improvement of power electronics has made it possible to increase the switching speeds of power devices. Switching frequency of several hundreds of kilo-Hertz is commonly adopted in switching power supplies. High-frequency operation can lead to a reduction of magnetic size and an increase of power density. As the frequency increases, the core loss becomes a limiting factor that cannot be ignored. Recently, coreless printed-circuit-board (PCB) transformers have been investigated for signal and power transfer [1]–[9]. It has been found that coreless PCB transformers can be used for high-frequency operation from about 200 kHz and upwards. The elimination of magnetic cores and the use of printed windings open a new way to manufacture low-profile transformers with high power density.