The power circuit diagram for two-quadrant type-B chopper, or type-D chopper, is shown in Fig.1.a. The output voltage $v_{0}=V_{s}$ when both $\mathrm{CH} 1$ and $\mathrm{CH} 2$ are on and $v_{0}=-V_{\mathrm{s}}$ when both choppers are off but both diodes $D 1$ and $D 2$ conduct. Average output voltage $V_{0}$ is positive when choppers turn-on time $T_{o n}$ is more than their turn-off time $T_{o f f}$ as shown in Fig.1.c.

Average output voltage $V_{0}$ is negative when their $T_{o n} \lt T_{\text { off }}$. Fig.1.d. The direction of load current is always positive because choppers and diodes can conduct current only in the direction of arrows shown in Fig.1.a. As $V_{0}$ is reversible, power flow is reversible. The operation of this type of chopper is shown by the hatched area in first and fourth quadrants in fig.1.b.