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 V_o -I₀  characteristics  is shown  in figure  that lie in second  quadrant.