This paper presents a mathematical model for proton exchange membrane fuel cells (PEMFCs) taking into account the basic electrochemical equations but including the boost power converter. This approaching is suitable for design and simulation of power electronics systems with embedded FCs as power supplies. The simplified model uses the Kirchoff's Voltage Law (KVL) applied to the conventional electric equivalent model of PEMFCs. This work is fully implemented in PSim (TM) as a general mathematical model and referred to literature data including the Boost converter, mostly used as the power interface for FCs. In this way, the model is fully evaluated by viewing the interface just as a power converter.