Isolated dc-dc converter is widely used in power system, especially in green power applications. Compared with the other circuits, full bridge converter is more suitable for power system, where high power and high voltage are involved. This paper proposes the full bridge converter with the uncontrolled rectifier. Three different operating modes and characteristics are analysed. Besides, this paper studies the impact of transformer's leakage inductance and the value of output inductor on the transformer's input current and transfer power. MATLAB simulation results are also shown to support the analysis.