## 1 Introduction
In the literature, one can find the results of experimental studies on Flyback power supply systems dedicated to the power supply of solid-state light sources. These sources were used in both Light Emitting Diode (LED) lamps emitting the entire visible spectrum used for room illumination [21] and white LED lamps used for roadway illumination in excess of 100 W [22]. The paper [23] presents the results of an experimental study on the use of a PID-controlled Reverse-Buck DC-DC converter with switching devices made of different materials. The use of GaN-based semiconductor devices improves the efficiency of the converter and enables operation at a higher switching frequency. Two different transistors were selected for experimental studies. As the first one, a JFET developed with the GaN technology was used, and as the other one, a MOSFET developed with the Si technology was used. The presented experimental results showed that better performance of the presented DC-DC converters was obtained for the JFET developed with the GaN technology, while it should be noted that the control circuit of this type of transistor is much more complicated than that of a Silicon transistor. The papers [24; 25; 26] discuss the results of measurements of currents drawn from the power grid and measurements of parameters determining the degree of distortion of these currents. The total harmonic distortion (THD) and power factor (PF) were indicated as parameters determining distortion. Mobile and smart home devices including power circuits in the Flyback topology and active PFC circuits are presented in [24; 25; 26]. The paper [26] discusses in detail the standards for the quality of current drawn from the power grid, which must be met by power consumers, whose rated current does not exceed 16 A per supply phase. Mobile devices require different kinds of electrochemical energy storage [27] for their operation, while different energy storage requires different voltage and power during the charging process. In order to eliminate the need for using different power circuits, the standardization of solutions is carried out, which specifically includes the USB-C connector standard and the USB PD charging standard in the latest version 3.1. In the papers [28; 29], the problem of temperature influence on the charging process of selected Li-Ion batteries and the problem of determining the State of Charge (SoC) level in mobile devices are considered. In the paper [28], the influence of temperature on the charging process parameters and durability of Li-Ion cells charged using fast charging techniques is analyzed. Measurements of the parameters of a Li-Ion cell during the charging process were carried out for two different arbitrarily selected operating temperature values of the cell. In turn, the paper [29] describes the problem of determining the SoC for mobile devices depending on the ambient temperature at which such a device operates. It was noted during the experimental studies that mobile devices operating at very low ambient temperatures, as low as \(-15\)\({}^{\circ}\)C, exhibit a very high SoC determination error. There are many charging systems on the market dedicated to operation with the USB PD standard and allowing fast charging (QC 4.0 and QC 4+) of mobile devices. These chargers also operate in the ACF topology and have a PFC circuit to improve the quality of current drawn from the power grid. Most USB PD charging circuits allow fast charging processes in the QC4.0 and QC 4+, and in the Extended Power Range (ERP) standard, which is the latest standard for USB PDs delivering up to 240 W of the output power. The main manufacturers of development boards containing dedicated charging circuits are ST Microelectronics (Geneva, Switzerland) (EVLVIPGAN100 PD [30], STEVAL-ISC004V1 [31]); Power Integrations (San Jose, CA, USA) (RDR-1002 InnoSwitch5-Pro [32]); Texas Instruments (Dallas, TX, USA) (SSZT522 [33]); and Infineon (Neubiberg, Germany) (XDPS2222 [34]).