In this study, the analysis and design of a coupled-inductor (CL)-based ultra-high step-up single-switch DC–DC converter are presented. With the aid of the CL and voltage multiplier cell, the suggested topology can obtain ultra-high-voltage gain without a large turn ratio and extreme duty cycle. A passive clamp circuit is utilised in the structure of the introduced converter for not only alleviating voltage spike on the main switch effectively but also recycle the leakage inductance energy. So low-voltage rating and low on-state resistance metal oxide semiconductor field-effect transistor is allowed to increase efficiency and lower the conduction losses. The input current ripple of the suggested topology is very low due to connecting an inductor to the suggested structure input section, which is very friendly and desirable to the photovoltaic and fuel cell applications. The suggested converter steady-state analysis, operation principle, theoretical efficiency analysis, and design procedure are described comprehensively in this study. Furthermore, the suggested converter superiority is illustrated over various alike recently introduced the most important DC–DC structures in the comparison study. Finally, a laboratory prototype is fabricated with a 225 W output power to confirm the theoretical analysis of the introduced converter. © The Institution of Engineering and Technology 2020.