Various mission-critical applications necessarily require a transformer in switching converters to obtain DC isolation between the converters’ input and output. Since DC-DC converters are the switching devices, these are modeled as hybrid automata. We present hybrid automaton modeling of two main types of transformer isolated DC-DC converters, namely, flyback and forward converters. We have also catered the non-determinism for both. We use HyST (Hybrid Source Transformation) tool to automatically generate the models in SpaceEx format, perform reachability analysis, and then automatically convert the models into Mathworks Simulink Stateflow (SLSF) using HyST. Thus we demonstrate effectiveness of HyST tool in the model-based design process. The HyST user needs not to manually construct or modify the models thus saving significant amount of time and efforts.