Abstract: Phase-shifted full-bridge converters have been widely used in small-volume isolated step-down applications. At the same time, in order to reduce the high-current pressure on the secondary side, dual inductors can be used for current doubling rectification, Shifted full bridge current-doubling synchronous rectifier converter (PSFB-CDSR). By simplifying the modal simplification, an equivalent circuit of a PSFB-CDSR converter based on a multi-cycle discrete iterative model is proposed. Compared with the traditional small signal model, the equivalent circuit model proposed in this paper can simultaneously describe the dynamics of each inductor current and output capacitor voltage of the converter, which is intuitive and accurate; and based on this, make assumptions about the parasitic resistance in the phase-shifted full bridge circulating current, and accurately describe the influence of the parasitic resistance on the power transmission characteristics; then the characteristic root of the state equation of the circuit model in the discrete domain is changed to obtain the stability margin under different input and output conditions influences. Finally, simulation results show the accuracy of the equivalent circuit and the correctness of the conclusion analysis.