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The demand for nonisolated high step-up dc-dc converters in applications such as dc backup energy systems for UPS, photovoltaic and fuel cell systems, and hybrid electric vehicles has been gradually increasing. This paper proposes nonisolated step-up dc-dc converters with an improved switching method. The proposed converter shows zero-voltage switching turn-on of the switches in continuous conduction mode as well as reduced turn- off switching losses owing to the switching method that utilizes Lr-Cr resonance in the auxiliary circuit. Also, as a result of the proposed switching method, the switching losses associated with diode reverse recovery become negligible even in the small duty cycle. The capacitance in the auxiliary circuit is significantly reduced compared to the pulsewidth modulation method. The duty cycle loss is further reduced resulting in increased step-up ratio. Experimental results from a 2-kW prototype of a two-phase interleaved version are also provided to validate the proposed concept.