Figure $(i)$ shows the circuit diagram of a chopper. The switch $S$ in the circuit in figure $(i)$ is switched such that the voltage $v_D$ across the diode has the wave shape as shown in figure $(ii)$. The capacitance $C$ is large so that the voltage across it is constant. If switch $S$ and the diode are ideal, the peak to peak ripple (in $A$) in the inductor current is ______