In this paper, a regulated output Buck-Boost DC DC converter is designed and simulated for photovoltaic energy system. The presented Buck-Boost converter has two power switches; moreover, its output voltage is regulated to a constant value regardless of its input. In the presented work, the Buck-Boost is used as a second converter after a Single Ended Primary-Inductance Converter (SEPIC) that is controlled with a maximum power point tracking technique (MPPT); Incremental Conductance MPPT algorithm is chosen to be used because of its simplicity and easy implementation. The Buck-Boost converter is controlled in a way to have a suitable output voltage by introducing the right duty cycle of the pulse width modulation signals that control the switches of the converter. The proposed configuration of Buck-Boost converter has been simulated in Matlab/Simulink environment; the simulation results show that it is a good choice to take in order to maintain the output voltage constant while ensuring a good energy transfer. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.