Investigation of Effect of Stray Capacitances in Air-Core Toroidal Transformer at High-Frequency Oscillation Based on Internal Magnetic Flux Density

An air-core toroidal transformer is a key passive component to achieve MHz operation of power converters. The stray capacitances of this transformer, determined by its structure, prevent fast switching. It is important to reveal the relationship between the structure and the stray capacitances for the design of this transformer. We measure the magnetic flux density of the fabricated air-core toroidal transformers with the different stray capacitances when they are operated in high-frequency switching conditions. As a result, the oscillation is observed in the measured input current and magnetic flux density. By comparing these transformers, it is found that the stray capacitances caused the oscillations.