This paper proposes a novel nonisolated single-switch cascaded high step-up converter. The converter consists of coupled inductors, a clamp circuit, and cascaded capacitors to achieve high step-up voltage output. Only one switch is used in the proposed converter; the switch can reduce cost efficiently and simplify the control of the proposed converter. The converter also possesses an energy-recycle mechanism for recycling the spike energy of a leakage inductor. In addition, a clamp circuit is used to reduce voltage-stress across the switch, and a cascaded design is used to reduce voltage-stress across diodes and output capacitor. Thus, the proposed converter can select a low-voltage stress switch for reducing circuit loss and improving the efficiency of the converter. Finally, in this study, a 400-W nonisolated cascaded high step-up converter was implemented, of which the input and output voltages are 48 and 400V, respectively. A microcontroller dsPIC30F4011 was used to control the converter and verify system effects and feasibility. The maximum efficiency of the proposed converter is 95% and the efficiency under a full load is 93%. Copyright (c) 2015 John Wiley & Sons, Ltd.