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 (approximate to 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.