Current Measurement and Synchronous Rectification at MHz+ Switching Frequency

Abstract

To achieve high-efficiency operation in high-frequency GaN-based resonant DC-DC converters, precise Synchronous Rectification (SR) plays an important role. However, in the MHz switching frequency range, reliable and accurate zero-detection becomes significantly challenging. In this frequency range, conventional sensing techniques have some problems, such as bandwidth limits, noticeable phase delays, and nonlinear behavior of magnetic cores. In this work, a coreless, PCB-integrated current sensing circuit based on the Rogowski coil principle is proposed. The proposed design uses the traces of a four-layer PCB to capture magnetic flux. Then it utilizes passive RC integration, differential amplification, and ultra-fast comparators to enable SR with minimal phase delay. The experiments are captured for a 1 MHz prototype of CLLC converter, showing a tight phase match between the current and the sensor output, demonstrating that the circuit can reliably drive SR switches and support highly efficient MHz-range power conversion.