The Micro Satellite Electric Propulsion System (MEPS) program has been originated by the increasing need to provide a low-cost and low-power Electric Propulsion System (EPS) for small satellites (<300Kg) and finds applications in orbit insertion after launcher separation, orbit maintenance, orbit transfers and deorbiting. The MEPS design was conceived as a "plug and play" subsystem that can be easily installed in a number of small spacecraft platforms, consisting of two Thruster Units (TU), Power Processing Unit (PPU), Xenon Propellant Tank Assembly (PTA) and Propellant Management Assembly (PMA). Being the "heart" of the system, the PPU supplies and monitors all the EPS voltages and currents. The objective of this paper is to present the design of the PPU whose concept is focused on high efficiency (> 92%), small size and weight and high reliability. Its functional modules and preliminary results obtained at breadboard level are also presented.