A Series/Parallel Magnetic-Less Step-Down Converter based on Piezoelectric Resonators

This study proposes a series/parallel piezoelectric resonator (SPPR) DC-DC converter that strives to improve performance at larger step-down ratios than what baseline piezo-resonator-based (PR) converters can nominally achieve. In the proposed converter, a series/parallel (SP) switched capacitor (SC) network is integrated into a traditional piezo-resonator-based step-down DC-DC converter to improve the performance of the piezo-based converter while maintaining most of the benefits of the traditional PR converter: zero-voltage switching and soft-charging of the junction capacitor in PRs. By leveraging the prestep-down property of the SC network, the optimal efficiency point can be shifted below the 2:1 ratio where the baseline PR-based converter is most efficient. Moreover, due to the piezoelectric resonator's inductive operation, the flying capacitor of the SC network can achieve soft charging/discharging over all operation ranges. A SPPR prototype is built with lead zirconate titanate (PZT) PRs to verify the operation of the proposed topology, demonstrating a peak efficiency of 95.27% at a 48V to 10V conversion ratio at 1.5W, and up to a 14.17% efficiency improvement over a baseline PR converter.