Transformers are magnetic components widely used in switched-mode power electronics systems. The non-linear hysteresis behavior of the magnetic material and the high frequency effects in both core and windings have significant effects on system's efficiency, reliability and power losses. This behavior can be modeled using simple fast models or complex accurate models in order to predict and improve the transformer behavior before realization. This paper is summarized by proposing a non-linear dynamic model of transformers for use in circuit simulators. This model allows winding and core modeling including the material's accurate nonlinear dynamic hysteresis behavior. The magnetic component model is implemented in the circuit simulation software " Simplorer " using VHDL-AMS modeling language. It is validated for a medium-frequency nanocrystalline core transformer. Effects of frequency and waveform on computed efficiencies are discussed and validated thanks to experimental measurements.