Dimensional Effects of Core Loss and Design Considerations for High Frequency Magnetics

To date, LLC Resonant converters, are deployed in many applications for improved efficiency, density, and reliability. With the introduction of WBG devices coupled with the soft switching feature, the switching frequency can be extended beyond MHz. With the significant increase in operating frequency, complicated magnetic components can be broken down into a cellular structure, each with few numbers of turns, and can be easily implemented using 4-6 layer of PCB windings. Moreover, integration of the cellular cores using flux cancellation can further improve the power density. The proposed integrated magnetics can be automated in the manufacturing process.With the recently developed high frequency core material, a phenomenon referred to as the dimensional resonant is observed. The effects of dimensional resonance were discussed in the literature when using an unusually large core structure; however, under high excitation frequency, it can be observed more frequently, and particularly with integrated magnetics. This paper discusses the dimensional effects of core loss on a PCB-based magnetics structure. A case study is presented on a 3 kW 400 V-48 V LLC prototype running at 1 MHz. The converter utilizes a low-profile matrix of two integrated transformers with a rectangular and thin cross-section area for reduced core loss. Specific solutions are presented.