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A novel high step-up DC-DC converter, which is composed of one boost converter, two capacitors, two diodes and one coupled inductor, is presented in this study. The concept is that the two capacitors are charged in parallel and are discharged in series via the coupled inductor to achieve high step-up voltage gain under appropriate duty ratio. Also, the leakage-inductor energy of the coupled inductor is recycled and the voltage stress on the main switch can be reduced. Besides, the energy of leakage inductor can transfer to capacitor to increase voltage gain. Therefore low conduction resistance RDS(ON) of the main switch can be adopted to reduce the conduction loss. In addition, the reverse-recovery problem of the output diode is alleviated. Thus, the efficiency can be further improved. The operating principle and steady-state analysis are discussed in detail. Finally, a prototype circuit with input voltage 24 V, output voltage 400 V and output power 200 W is implemented in the laboratory to verify the performance of the proposed converter.