Second Quadrant or Class B Chopper
Class B chopper is shown in figure in this type of chopper load must contain a dc source E ( may be battery or a DC motor) and inductances the operation of classes B chopper as follows.
Mode I
When SW is on V0 = 0 but current will be flowing through inductance L and chopper SW due to E as shown in figure in this mode inductance L stores energy.
Figure shown the polarity of inductance and direction of load current. It is clear from this figure that this polarity's same as in directed but the current is flowing in reverse direction. Hence is negative.
Mode II
When SW is off V0= { E+ L di0/dt} exceeds the Vs therefore diode D becomes forward biased and current flow load to source through diode D. Again the load voltage is positive but current is in negative direction. In this mode inductance releases energy and the polarity is shown in figure.
Hence the Vo -I0 characteristics is shown in figure that lie in second quadrant.