Virginia Polytechnic Institute and State University
Planar transformers with PCB winding are increasingly popular in modern power conversion systems due to their controllable design and high-power density. The high-frequency operation enables small core volume, but also introduces undesirable effects such as current redistribution within the windings, increasing conduction loss. To handle high AC currents, multiple winding layers are connected in parallel. However, current sharing among these parallel layers can be influenced by a magnetic core air gap, which degrades the effectiveness of parallel windings. Previous research on air gap effects has mainly focused on fringing flux mitigations. In contrast, the impact of the air gap on current sharing among parallel windings has not been thoroughly investigated. To address this gap, this paper presents a simple analytical model for predicting current distribution in parallel windings while accounting for the air gap effect. The model is derived from the electrical circuit of the transformer and provides both efficient evaluation of winding configurations and air gap positioning, as well as physical insight into the mechanisms governing current sharing in planar transformers
