The synchronous rectifier (SR) turn-off time should be accurately controlled to achieve zero voltage switching (ZVS) while minimizing circulating current in pulsewidth modulation converters operating at critical conduction mode. Traditionally, the zero-crossing of the inductor current needs to be detected, and the optimal SR turn-off time is set with reference to the zero-crossing signal. However, problems such as nonlinearity and time delay need to be dealt with, and these make the tuning process very time-consuming at high frequencies. Moreover, accurate zero-current detection is also challenging at high frequencies. This letter proposes an adaptive SR turn-off time tuning method for MHz power converters. The body diode conduction of active switch is detected to adjust the SR turn-off time. With the proposed method, the SR turn-off time can be tuned under various working conditions so that ZVS is achieved while circulating current is minimized. The proposed scheme is easy to implement and not sensitive to switching noise at high frequencies. A 500-W gallium nitride based boost converter is built to verify the proposed method, and the peak efficiency reaches 99% at 1 MHz.

中文翻译：

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ZVS 的自适应驱动方案和最小化 MHz CRM 转换器中的循环电流

同步整流器 (SR) 关断时间应精确控制，以实现零电压开关 (ZVS)，同时最大限度地减少在临界导通模式下运行的脉宽调制转换器中的循环电流。传统上，需要检测电感电流的过零，并参考过零信号设置最佳SR关断时间。然而，非线性和时间延迟等问题需要处理，这些使得高频调谐过程非常耗时。此外，准确的零电流检测在高频下也具有挑战性。这封信提出了一种适用于 MHz 功率转换器的自适应 SR 关断时间调谐方法。检测有源开关管体二极管导通，调整SR关断时间。使用所提出的方法，SR 关断时间可以在各种工作条件下进行调整，从而在最小化循环电流的同时实现 ZVS。所提出的方案易于实现并且对高频开关噪声不敏感。构建了一个 500-W 氮化镓基升压转换器来验证所提出的方法，峰值效率在 1 MHz 时达到 99%。