\documentclass{article}
\usepackage{graphicx}

\begin{document}
\begin{figure}
	\center
	\includegraphics[width=0.5\textwidth]{ChargingCircuit.png}
	\caption{Charging circuit with 50v DC source as load}
\end{figure}

\begin{figure}
	\includegraphics[width=\textwidth]{iL50v.png}
	\caption{Current through inductor with 50v DC source as load}
\end{figure}
\begin{figure}
	\includegraphics[width=\textwidth]{iL100v.png}
	\caption{Current through inductor with 100v DC source as load}
\end{figure}
\begin{figure}
	\includegraphics[width=\textwidth]{iL150v.png}
	\caption{Current through inductor with 150v DC source as load}
\end{figure}
\end{document}