## 5 Conclusions  
Energy converters make it possible to supply electricity with the appropriate parameters. When a direct current needs to be supplied, rectifier diodes are used in their design. Thermographic diagnostics of rectifier diodes make it possible to extend their service life, adjust the operating location to the design assumptions, verify the choice of heat sink, and even prevent failure. Consequently, it is possible to reduce operating costs. The smallest difference between the temperature obtained from the simulation work and the experimental work was obtained at point 3-0.1 \({}^{\circ}\)C (Figure 5, Table 6). On the \begin{table}
\begin{tabular}{c c c c c c} \hline
**No.** & \(P_{j}\) **(W)** & \(\
u\) **(m/s)** & \(T_{c}\) **(C)** & \(T_{j}\) **(C)** & \(T_{j}-T_{c}\) **(C)** \\ \hline \multirow{8}{*}{1} & & 0.75 & 52.6 & 56.3 & 3.7 \\  & & 1 & 48.4 & 53.5 & 5.1 \\  & & 1.5 & 42.4 & 50.8 & 8.4 \\  & & 0.75 & 54.8 & 56.3 & 1.5 \\  & 46.23 & 1 & 51.3 & 53.5 & 2.2 \\  & & 1.5 & 45.2 & 50.8 & 5.6 \\  & & 0.75 & 39.2 & 56.3 & 17.1 \\  & & 1 & 37.1 & 53.5 & 16.4 \\  & & 1.5 & 33.3 & 50.8 & 17.5 \\  & & 0.75 & 67.6 & 77.5 & 9.9 \\  & & 1 & 59.4 & 70.5 & 11.1 \\  & & 1.5 & 56.9 & 67.4 & 10.5 \\  & & 0.75 & 71.9 & 77.5 & 5.6 \\
2 & 74.48 & 1 & 64.5 & 70.5 & 6.0 \\  & & 1.5 & 61.5 & 67.4 & 5.9 \\  & & 0.75 & 48.2 & 77.5 & 29.3 \\  & & 1 & 42.5 & 70.5 & 28.0 \\  & & 1.5 & 38.2 & 67.4 & 29.2 \\  & & 0.75 & 92.4 & 107.5 & 15.1 \\  & & 1 & 72.8 & 91.2 & 18.4 \\  & & 1.5 & 66.6 & 86.4 & 19.8 \\  & & 0.75 & 98.4 & 107.5 & 9.1 \\
3 & 111.75 & 1 & 80.3 & 91.2 & 10.9 \\  & & 1.5 & 74.0 & 86.4 & 12.4 \\  & & 0.75 & 65.1 & 107.5 & 42.4 \\  & & 1 & 47.9 & 91.2 & 43.3 \\  & & 1.5 & 43.4 & 86.4 & 43.0 \\ \hline \end{tabular}
\end{table} 
Table 7: Comparison of the results obtained from the \(T_{\rm C}\) measurements and the junction temperatures \(T_{j}\) determined. contrary, the smallest difference between the temperature of the case and the temperature of the junction was obtained at point 1-1.5 \({}^{\circ}\)C (Figure 5, Table 4). On the basis of the experimental work carried out, the effectiveness of thermographic diagnostics under forced convection conditions can be confirmed. It was confirmed that, for air velocities not exceeding 1.5 m/s, it is possible to carry out an indirect thermographic measurement of the junction temperature of a semiconductor diode, i.e., a measurement whereby the junction temperature of the semiconductor can be determined from the measured temperature of the case. To perform this, it is necessary to monitor point 1 shown in Figure 5.  
The value of the convection coefficient increases with increasing air velocity and decreases with increasing surface temperature. In the work carried out, the value of the convection coefficient ranged from approximately 21 to approximately 77. This value depends on the shape of the surface, on the orientation of the surface, and on the speed of the air that flows around the surface. By analyzing the thermograms shown in Figure 7, it can be seen that, as the airflow velocity increases for the same Pj power values that were discharged at the junction, the recorded temperatures of the heat sink and the diode case are lower. This indicates an improvement in heat dissipation from these surfaces. This trend can be seen for all the power values of Pj that were discharged. The temperature distributions that were determined from the simulation work (Figure 8) confirm the thermographic measurements. Consequently, it is possible to conclude that the recorded thermograms are reliable. It can also be concluded that, for air velocities of no more than 1.5 m/s, the thermographic measurement of the surface temperature of the power diode and the heat sink (on which it is placed) is reliable. By analyzing the data in Table 6, it can be seen that the temperature obtained on the surface Tc differed from the joint temperature Tsym, which was determined from the simulation work. The smallest differences can be observed for point 2 (shown in Figure 5).