This type of chopper is shown in Fig.1.a. In Fig.1.a , when chopper CH1 is on, $v_{0}=V_{s}$ and current $i_0$ flows in the arrow direction shown. When CH1, is off $v_{0}=0$ but $i_{0}$ in the load continues flowing in the same direction through freewheeling diode $\mathrm{FD}$. It is thus seen that,average values of both load voltage and current, i.e. $V_{0}$ and $i_{0}$ are always positive. This fact is shown by the hatched area in the first quadrant of $V_{0}-I_{0}$ plane in Fig.1.b.

The power flow in type-A chopper is always from source to load. This chopper is also called step-down chopper as average output voltage $V_{0}$ is always less than the input d.c. voltage $V_{s}$ .