\begin{tikzpicture}[>=latex]
\matrix[]
{
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,0.225) -- (0.18,0);
      \fill[gray!30] (4,0) -- (1.2,0) -- (1.2,0.225) -- (4.0,0.225);
      \fill[gray!60] (0.18,0) -- (1.2,-1.275) -- (1.2,0);
      \draw (0,0.225) -- (1.2,-1.275) -- (1.2,0.225) -- (4,0.225);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.2,0.225) -- (1.2,0.225) node[above] {$T_1$};
      \draw (3.0,0) -- (3.0,-0.1) node[below] {$T_2$};
      \draw (4.0,0) -- (4.0,-0.1) node[below] {$T_s$};
      % vertical axis
      \draw[->] (0,-1.7) -- (0,1.0) node[above] {$i_{C_{in}}(t)$};
      \draw (0,0.225) -- (-0.1,0.225) node[left] {$I_{in}$};
      \draw (0,-1.275) -- (-0.1,-1.275) node[left] {$i_2$};
      \node at (2.0,-3.5) {$\text{I: } \min i_L = 0$};
&
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,0.28) -- (0.224,0);
      \fill[gray!30] (4,0) -- (1.6,0) -- (1.6,0.48) -- (4.0,0.48);
      \fill[gray!60] (0.224,0) -- (1.6,-1.72) -- (1.6,0);
      \draw (0,0.48) -- (0,0.28) -- (1.6,-1.72) -- (1.6,0.48) -- (4,0.48) -- (4,0.28);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.6,0.48) -- (1.6,0.48) node[above] {$T_1$};
      \draw (4.0,0.48) -- (4.0,0.48) node[above] {$T_s$};
      % vertical axis
      \draw[->] (0,-3) -- (0,1.5) node[above] {$i_{C_{in}}(t)$};
      \draw (0,0.48) -- (-0.1,0.48);
      \draw[<-] (-0.3,0.53) -- (-0.7,0.68);
      \node[left] at (-0.7,0.8) {$I_{in}$};
      \draw (0,0.28) -- (-0.1,0.28);
      \draw[<-] (-0.3,0.25) -- (-0.7,0.08) node[left] {$i_1$};
      \draw (0,-1.72) -- (-0.1,-1.72) node[left] {$i_2$};
      \node at (2.0,-3.5) {$\text{II: } 0 < \min i_L < I_{in}$};
&
      \pgftransformscale{.7}
      \fill[gray!30] (4,0) -- (1.6,0) -- (1.6,1.2) -- (4.0,1.2);
      \fill[gray!60] (0,0) -- (0,-0.8) -- (1.6,-2.8) -- (1.6,0);
      \draw (0,1.2) -- (0,-0.8) -- (1.6,-2.8) -- (1.6,1.2) -- (4,1.2) -- (4,-0.8);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.6,1.2) -- (1.6,1.2) node[above] {$T_1$};
      \draw (4.0,1.2) -- (4.0,1.2) node[above] {$T_s$};
      % vertical axis
      \draw[->] (0,-3) -- (0,1.5) node[above] {$i_{C_{in}}(t)$};
      \draw (0,1.086) -- (-0.1,1.086) node[left] {$I_{in}$};
      \draw (0,-0.8)  -- (-0.1,-0.8)  node[left] {$i_1$};
      \draw (0,-2.8) -- (-0.1,-2.8) node[left] {$i_2$};
      \node at (2.0,-3.5) {$\text{III: } \min i_L \geq I_{in}$};
\\
};
\end{tikzpicture}
