EMI analysis of a DC-DC converter using a piezoelectric transformer

Power electronic converters based on piezoelectric transformer (PT) have been widely adopted in recent years due to their many inherent advantages such as safety, low housing profile and high power density. However, few studies have been conducted about noises emitted by PT converters. In this paper, we study conducted EMI problems in a 10 W, DC-DC PT converter. The different sources and specific couplings of EMI in this structure will be presented. The experimental setup, which allowed us to study the various propagation ways and to measure the relevant impedances will be shown. A model which focuses on the parasitic impedances of the PT connected to the rectifier will be proposed. It will be shown that the EMI behaviour of a PT based converter is very different from usual power electronics, due to the PT structure and to its specific output working. Furthermore, the experimental validation of our model is discussed. Finally, we propose an improved configuration of the staked disk-type PT in the converter to reduce the common-mode noise. As a result, drastic noise reduction has been achieved.