Low-latency High-speed Saturable Transformer based Zero-Crossing Detector for High-Current High-Frequency Applications

This paper proposes a simple detection method for zero-crossing events of converter current using a saturable transformer for use in high-current and high-frequency pulse-width-modulated power electronic converter applications. Design goals include attaining high sensitivity, noise immunity, and efficiency with very low latency (≈ 20 ns) which is essential for the implementation of current control methods requiring very high control-bandwidth. The proposed zero-crossing-detector (ZCD) is ideally suited for cycle-by-cycle current control in interleaving and/or soft-switching applications, which overcomes the limitation posed by typical current transducers for such applications. Comparative analysis between three different designs: T46 ferrite, off-the-shelf nanocrystalline core, and a modified nanocrystalline core, has been performed using finite-element-analysis (FEA) to achieve an optimized design with regard to thermal efficiency and sensor latency. A signal conditioning circuit for digital output has also been provided. The proposed analysis and design have been validated through laboratory experiments.