Gain-adjustment Technique for Resonant Power Converters with Piezoelectric Transformer

In power processing applications, switching power converter research have focused on the potential feasibility of piezoelectric transformers (PTs) for cost competitiveness, size effect and good EMI characteristics. However, the PT has a voltage conversion limit because of its physical dimensions and manufacturing procedures. The fact can be a restriction to a circuit engineer facing new application design with PT because of its in adaptivity to extreme conversion ratios of emerging applications. In order to overcome this problem, tapped inductor is introduced. The tapped inductor can transform the input voltage into the adequate level by its own turn-ratio. Consequently, this tapped inductor scheme with piezoelectric transformer makes it possible to obtain both PT´s advantages and conversion gain adjustment without part-count increase. For the proposed converter evaluation, this paper provides the operation analysis and design procedures of the converter, and presents the experimental verification with a 20-W hardware prototype DC/DC converter as well. Finally, topology extension is also presented by combining tapped-inductor with other conventional resonant converters with piezoelectric transformer.