First Quadrant or Class A chopper

A chopper  two mode operation of class  A chopper  can be explained as follow.

                                                             Figure class A  chopper  circuit  V₀- I₀ characteristic

Mode I 

When  the chopper switch  is on V₀= V_s  and current  flows in the direction  in this mode  V₀ and I0  will be  positive.

Mode II

When the chopper SW  is OFFF V₀ = 0 (Since  diode  act like short Circuit). Now  the inductor present in the load releases its energy and  maintain the current in  the same direction through  the freewheeling diode FD.  Again the V⁰  and I0 will be  positive. This  operation is shown in by the hatched area in figur.