The paper presents the steady-state analysis of the step-up/step-down operation of the full bridge resonant transition converter (FBRTC). In spite of several work being reported in the literature on the FBRTC converter, the performance differences during the step-up and step-down operations are less investigated. Influence of leakage inductance, magnetizing current of the transformer and switching frequency on the steady-state DC-voltage gain of the step-up/step-down converters is presented with the supporting results. The iterative design methodology for the step-up/step-down converters are proposed to enhance the efficiency. The investigation carried out in this work help the designer to select the appropriate leakage inductance, magnetizing inductance, turns ratio of the transformer and switching frequency of the step-up and step-down converters. The analysis and design methodology are validated in simulations. The performance analysis is verified in a 500 W experimental prototype. © 2020 IEEE.