Fully-Integrated Planar Transformer With a Segmental Shunt for LLC Resonant Converters

Abstract

This article presents two topologies, which provide high leakage inductance in shunt-inserted integrated magnetic transformers. These differ from conventional designs by replacing the low-permeability magnetic shunt of a planar transformer with high-permeability magnetic shunt segments, separated by many small air gaps. This approach results in a shunt with the same bulk permeability as the conventional design, while using lower cost and readily available magnetic materials such as ferrite. A modeling and design approach, which can estimate the leakage and magnetizing inductances precisely is provided for each topology. Theoretical analysis is presented and verified using finite-element analysis and experimental implementation. Ac resistance analysis for both transformer topologies is also presented. In addition, an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter is built to verify the performance of the proposed fully-integrated magnetic transformers in practice. It is shown that the proposed topologies can integrate all three magnetic components of an isolated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter in a single planar transformer, which reduces the converter's volume and cost.