Type B Chopper In type B or second quadrant chopper the load must always contain a dc source E .  When the chopper   is on, v0   is zero but the load voltage E drives the current through the inductor L and the chopper, L stores the energy during the time Ton of the chopper . When the chopper is off , v0 =( E+ L .  di/dt )  will be more than the source voltage  Vs . Because of this the diode D2 will be  forward biased and begins conducting and hence the power starts flowing to the source.  No matter the chopper is on or off the current I0  will be flowing out of the load and is treated negative . Since VO  is positive and  the current I0  is negative , the direction of power flow will be from load to source. The load voltage V0  = (E+L .di/dt )   will be more than the voltage Vs  so the  type B chopper is also known as a step up chopper.