An Isolated High Step-Up Converter Based on the Active Secondary-Side Quasi-Resonant Loops

Resonant converter is a good solution as the isolated high step-up converter due to its soft-switching features and less component count. However, since the resonant tank is placed on the primary side (low-voltage side) in most traditional resonant converters, large input current still leads to a big proportion of power loss. Besides, synchronous rectification (SR) is also a big issue. The diode conducting time in a resonant converter is hard to be predicted so a current transformer or an analog SR chip is usually employed to detect the current zero-crossing point when the higher efficiency is required. In this article, an isolated high step-up converter with active secondary-side quasi-resonant tank is proposed. Since the whole resonant tank is placed on the high-voltage side, the current stress of the resonant capacitors and their power loss can be greatly alleviated. Besides, the analytical solution of the diode conducting time is derived and two SR control schemes are proposed, without the need to detect the current zero-crossing point. All the switches and diodes achieve the soft-switching so this leads to a good efficiency performance. The validity is confirmed by the experimental results of a 500 W prototype with 36-48 V input and 380 V output.