Two Quadrant Type A Chopper or Class C Chopper or Reversible Chopper
The quadrant type A Chopper is also known as reversible chopper because the polarity of the load current can be reversed.
Mode I
When SW1 is ON V0= Vs and the direction of current is shown as figure therefore current I0 and voltage Vo will be positive.
When SW1 of OFF V0 =0 but now load inductor releases the energy and current is maintained in the same direction. In this case V0= 0 because the polarity of inductance will be reversed and VL = -E therefore.
V0 = VL + E = -E + E =0
Hence the Vo - Io characteristic is drawn in first quadrant since both V0 = I0 are positive as shown in figure.
Mode II
When SW2 is on Vo + 0 but current will be flowing from load t oSW2 in negative direction. Inductance stores energy due to E2.
When SW2 is off Vo = E +L di / dt exceeds Vs and therefore diode D is forward biased and current flows from load to source through diode D.
Hence the Vo -I0 characteristics for mode II is drawn in second quadrant since Vo is positive but I0 is negative as shown in figure.