Planar Piezoelectric Transformer-Based High Step-Down Voltage-Ratio DC–DC Converter

High step-down voltage-ratio converters are widely used in medium-/high-voltage systems, such as solar power equipment and electric charging station as auxiliary power supplies fed from the dc bus. Traditionally, magnetic transformer-based solutions with high turns ratio are implemented for voltage conversion and galvanic isolation. Instead of utilizing electromagnetic coupling, the high-voltage Rosen-type piezoelectric transformer (PT) provides an alternative solution with electro-mechanical coupling, whose equivalent circuit can be represented by a resonant circuit with an ideal transformer. Moreover, the high-voltage Rosen-type PT features natural mechanisms for high-voltage insulation, high-voltage conversion ratio, and a compact planar form factor, which are all beneficiary for a high step-down auxiliary power supply. This article renders a Rosen-type PT-based high step-down voltage-ratio converter with comprehensive analysis and detailed design procedure. To better understand the operating principle, electrical characteristics of the PT are first analyzed. Effects of input and output compensation components of the PT and their tolerance analysis are subsequently discussed to optimize the performance. After that, topologies of both the input inverter and the output regulation stages are selected. The proposed design is finally validated by a planar prototype with 10-mm height, 5 W full output power, 200 V to 1.5 kV input voltage, and 5 V regulated output voltage.