A Simple Method to Build a Linear Circuit Model for a Multi-Winding Transformer Used in EMI/EMC Analysis

This practical paper presents an easy-to-use technique for identifying lumped parameters of equivalent circuits for multi-winding transformers. The equivalent circuit helps in modeling the EMC noise. This work takes two paths to create linear models for a multi-winding transformer: RLC with physical meaning of all components, but limited to 10 MHz, and a nine-port S-parameter black-box model, but valid up to at least one GHz. The method is illustrated on a single core transformer with four windings used in a flyback converter for an automotive 40-1000 V input auxiliary power supply for an 800 V battery system.