An averaged modeling technique for DC to DC converters has been developed and applied to the DC to DC Converter Unit (DDCU) of the Space Station Freedom. The averaged model can be used for frequency domain, transient, and steady-state simulations. The DDCU model derivation is included to demonstrate a technique for modeling other complex topologies. The equations for a special case of the Weinberg topology where the power transformer and flyback transformer turns ratios are different are also included. Averaged modeling results have been correlated with test data as well as linearized small signal and full order switching model results.