Reducing SMPS Conducted Emissions with Three-Winding Transformers

Besides a traditional two-winding transformer, a three winding version was analyzed as well. Multiwinding transformers typically are used to achieve several output voltages. In the case presented here, the third winding was used to create a shield to reduce the conducted emissions from an SMPS. The shielding effect was obtained through appropriate connection to the primary winding. This is a quick and economical way to generate a shield; production time is not appreciably increased. The equivalent circuit was optimized for use in the PSpice circuit simulator. The simulation of a flyback SMPS allowed the benefits obtained by using the shielded transformer, with respect to conducted emissions, to be evaluated. All simulations were validated experimentally and shown to be in satisfactory agreement with real-world results.