Techniques of the Modeling, Measurement and Reduction of Common Mode Noise for a Multi-winding Switching Transformer

The reduction of common mode (CM) noise for isolated converters has been a popular research topic. This paper proposed a generalized two-capacitor modeling technique for switching transformers with multiple windings and complicated winding structures. Based on the proposed model, a Flyback transformer with multiple winding structures is investigated. A new measurement technique to characterize and evaluate switching transformer's CM noise performance is developed. Only a signal generator and an oscilloscope are needed for the measurement and no any in-circuit tests are needed. The technique can help to quickly design and evaluate transformers for CM noise reduction in mass testing and production. CM noise reduction techniques including balance capacitor technique, core shielding technique and winding design technique are developed based on the developed two-capacitor model and measurement technique. Experimental results verify the proposed model and the developed CM noise reduction techniques.