This paper is based in its first part on basic information about solar energy and photovoltaic systems. The general features of PV modules and PV cells and their current-voltage characteristics are described. Then, the basic characteristics of a step-down DC converter without galvanic isolation are analyzed and its continuous and discontinuous operating modes are explained. In the fourth chapter, the capabilities of the Magna-Power DC source are described, where detailed instructions are given for all its control settings located on the front panel of the device. Since this source can also be controlled via a computer, using a special interface (Remote Interface Software Panel), all associated components are described. After that, the operation of the DC source in the constant voltage (CV) and constant current (CC) modes is shown. The procedure for programming the current-voltage characteristics, which enables emulation of PV modules, is also explained. A laboratory model of the system under consideration is assembled, in which the DC source is connected to a variable operating load via a step-down DC converter without galvanic isolation. Using a model, experimental results were recorded for various examples illustrating the above operating modes of the DC source.