High-Efficiency Operating Modes for Isolated Piezoelectric-Transformer-Based DC-DC Converters

The drive to miniaturize power electronics motivates investigation into alternative converter energy storage technologies such as piezoelectrics, which offer fundamentally higher power density and efficiency capabilities compared to magnetics. Piezoelectric transformers (PTs) have seen utilization in dc-dc converter designs, but typically alongside magnetics or with limited/unreported efficiency. In this work, we systematically enumerate isolated dc-dc converter operating modes and topologies that utilize PTs as their only energy storage components. The proposed operating modes leverage simple converter topologies to maintain high-efficiency behaviors (e.g., zero voltage switching (ZVS) and all-positive instantaneous power transfer) across wide operating regions. We present techniques for deriving these operating modes' ZVS regions, estimating PT efficiency, mapping switching sequence combinations to the PT's resonant cycle, and solving for periodic steady state and switching times; these offer insights for comparing and implementing design options. We then illustrate an example design and verify our analyses using LTspice simulations, which attest to the high potential capabilities of dc-dc converters based on strategically-utilized PTs.