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Piezoelectric power converters, where acoustic resonators replace the inductors as energy storage elements, promise much higher power density and higher efficiency compared to conventional circuits. Recently, lithium niobate (LiNbO3) piezoelectric resonators have been integrated within power converter circuits, showing good conversion efficiency, thanks to their high quality factor ( ${Q}$ ) and electromechanical coupling ( ${k}_{t}^{\,{2}}$ ). However, the converter output power range is limited by large spurious modes near resonance. This work reports a near-spurious-free LiNbO3 thickness shear (TS) resonator, demonstrating a high ${Q}$ of 3500 and ${k}_{t}^{\,{2}}$ of 45% at 5.94 MHz, with a fractional suppressed region of 35%. First, we identify the best LiNbO3 crystal orientation for efficient TS resonators. Then, we propose a novel acoustic design without busbars for spurious suppression, which is extensively simulated, fabricated, and characterized. Further analysis is done to identify existing spurious modes in our proposed design, specifically the effect of dicing on our TS resonator design. Upon optimization, LiNbO3 TS resonators could potentially empower a new design space for low-loss and compact power converters.

In this article, an auxiliary circuit-based soft-switching mechanism for a high-gain, nonisolated, four-phase interleaved hybrid boost converter is presented. The auxiliary circuit consists of only a single additional switch, four diodes, and a small auxiliary inductor, and ensures zero voltage transition (ZVT) of all four phases. Two variations of the ZVT circuit application are presented in this article, each having its own advantages and can be implemented without any significant modifications in the auxiliary circuit. The auxiliary switch operates with zero current switching, ensuring that the power loss in the auxiliary circuit is low for both cases. The timing of the ZVT circuit is adaptively controlled with changing load conditions. The proposed concepts are validated through a 2.5 kW hardware prototype operating at 100 kHz and achieving a high gain conversion from 46 V input to 850-V output. The converter is able to achieve a peak efficiency of 98.3% with silicon devices as main switches at 100-kHz switching frequency.

Applying RF circuit design techniques to dc-dc resonant converters has enabled switching frequencies well beyond 10 MHz, leading to higher power densities and faster transient response. Synchronous rectification is advantageous for low-voltage high-power applications but is challenging to implement in a high-frequency (HF) dc-dc converter. This article proposes an HF/very HF (VHF) resonant converter structure in which the rectifier and the inverter switches can be driven with the same gate signal. The presented structure enables efficient bidirectional power delivery in the HF/VHF range for applications that require a large voltage conversion ratio. A 64-MHz, 12-W, 36-12-V prototype converter verifies the operation of the structure. This article further explores an interleaved architecture of the same circuit to improve efficiency and transient performance. Finally, a 13.56-MHz 210-30-V prototype converter with 90% peak efficiency at 200 W demonstrates the advantages of the interleaved architecture.

A novel converter based on the differential connection of a switched capacitor (SC) and buck-boost converter is presented in this article. This converter enables volume reduction while also increasing power processing efficiency by utilizing the high power density of SC converters and partial power processing. The introduced multioutput inverting buck-boost SC converter is presented as a light-emitting diode (LED) driver for mobile applications. The topology is capable of providing current to multiple LED strings at different voltages. A current-balancing technique based on charge matching is developed without the need for external-current-regulating components. Experimental results confirm a reduction in passive volume around 70% compared to conventional topologies for the targeted application while also increasing efficiency over the whole range, with a peak efficiency of 93%. In particular, light-load efficiency is improved up to 20%. The operation of the proposed charge matching control is confirmed through experimental and simulation results.