The virtual prototyping of power electronic converters is considered here. Virtual prototyping is now an important challenge in the context of integration of power systems. If semiconductor devices are considered as the levellers of significant advances in power converters, it is commonly admitted that the next leveller of advances is related to the design methods. The design methods ambition to deliver a satisfying product with the first prototype as a prototype of a power converter is expensive. Differences in virtual prototyping acceptance may be foreseen depending on the level of integration. On the one hand VLSI power management requires methodologies and models in the framework of integrated circuit tools. The dedicated tools seem to dictate the nature of the models and of the design flow. On the other hand the design of a mechatronic system could rely on a wider range of models and methodologies depending on the background of the involved engineer. In fact the development of virtual prototyping methodologies try to provide a systematic approach to the different steps involved in the emergence of a product. Depending on the complexity of a given system, all or parts of the models and analyses will be solicited. The idea is that a simple step-down DC/DC converter represents a similar design problem whether a 1 W monolithic IC is required or a 100 W discrete-board converter inside a car mechatronic-item is specified. The common part in the design process of these two seemingly different converters concerns the early stage of virtual prototyping, namely the pre-design. Fig. 1 details the macro-steps in the design flow of a power converter, but the idea is applicable to a mechatronic device. Pre-design covers the early steps in the design flow. Other steps in the design process will involve hard technology constraints, what will affect the complexity level of some models but design analyses remain essentially the same whatever the level of integration. These intermediate steps in the design process refer to what is practically known as design, what is in essence to choose devices and to optimize circuits. When device and circuits have been globally optimized, next steps concern the geometrical and physical assembly of these devices into a converter. Additional physical phenomena appear that require dedicated tools and models to complete the optimization of the power converter. The final steps in the design process concern the virtual physical verification of the system. The technology constraints and the geometrical size of the system, adding the power level, dictate different approaches for the analyses to be carried out. The latter verification efforts are in relation to the system specifications and receipt.