Investigation and Solutions for High Termination Losses in Planar Matrix Transformers with Full-Bridge Rectifiers

High-frequency resonant converters with planar matrix transformers have become ever more popular in datacenters and automotive applications, due to their high power densities and high levels of efficiency. For high-frequency, high-current applications, careful design of the transformer termination is crucial for minimizing termination losses. This paper discusses different termination techniques for full-bridge secondary rectifiers (SRs) in planar matrix transformers. However, if not designed carefully, the higher number of devices in full-bridge SRs can cause high termination losses, resulting in lower efficiencies. Placing SRs and filter capacitors directly on secondary windings reduces the termination loop and is deemed the best option for low-loss termination. However, distributing the SRs and capacitors on the top and bottom secondary layers results in parallel resonance, and hence circulating currents between the rectifier capacitors. This can introduce high termination AC resistance if the parallel resonant frequency is close to the converter switching frequency. This behavior is also investigated in this paper. Solutions, verified with hardware, are introduced with the goal of minimizing the circulating current losses.