Modelling and design of planar PCB transformers for high-frequency DC-DC converters

Abstract

The demand for high density power supplies has been increasing through the years. The most common trend in achieving high power density is to use high frequency switching which results in smaller component size. However, for the magnetic components, operation at high frequencies leads to increased conductor losses due to skin and proximity effects. The use of planar transformers on printed circuit boards (PCB) can mitigate this problem. The thinner and wider conductors of PCBs assist in reducing high-frequency losses. With larger surface areas, planar transformers also offer better thermal performance than conventional wire-wound magnetics.

In this thesis, research activities to further the technology of planar PCB transformer are presented. These research activities are aimed at improving the modelling, design and utilization of planar PCB transformers for high-frequency power converters. A new non-linear model of planar PCB magnetics was developed to model the winding loss, core loss, and saturation characteristics. The developed model can be implemented in a circuit simulation package which can be used to predict the performance of the PCB transformer in a power converter system. The model was also used to derive the high-frequency electrical parameters of a PCB transformer. The model-derived parameters were proven to be comparable to LCR measurement and results obtained using finite element analysis. A stochastic method of estimating the electric parameters of a PCB transformer, based on differential evolution, was also developed. The developed method was shown to be a potential alternative to resource-intensive numerical methods.

Existing guidelines for the design of PCB transformers are evaluated using finite element analysis and validated in a prototype transformer. Results of the evaluation show that the existing guidelines result in over-design of PCB transformers. For higher power applications, using the high-frequency advantage of PCB transformers, methods to implement multiple planar PCB transformers, including the concept of matrix transformer, are presented and compared. Through the evaluated design guidelines, prototypes of multiple core transformers were fabricated and characterised in a power converter system. Result of the comparison of the different implementations showed that the trade-off is between high-frequency losses and thermal dissipation.