Four  Quadrant Chopper or Class E chopper

                                                                 Figure class E chopper circuit

 Mode I

When SW₁  is ON  with SW₄ V0 = Vs and load current  flows  as shown  in figure  when SW1 is OFF  V0 = 0  but current  will continuously be flowing  through  SW_$ and diode  D₂. Here both V₀ and I0 will be positive hence it is first quadrant operation as shown  in figure.

Mode II

When SW₂  is ON  with diode D₄ V₀= 0 but the  direction of current  will be  negative.  When SW₂  is OFF diode D₁  and D₄  will be conducting  in this period  power flows  from load  to source  because V0 = E+ L di/dt exceeds Vs. Hence  Vo is positive  but current  is negative. This give the  second  quadrant operation as  show in figure.

Mode III

In this  mode the  polarity off must  be reverses so that  third  quadrant operation can be  obtained. Now  when SW2 is ON with SW2 , V0 = -Vs and  current will  be flowing in reverse direction. Both  V_o  and Io  will be  negative. When SW₃ is OFF D₂ will conduct with  SW₂ therefore  both V0 and Io  will be  negative. Hence third  quadrant operation is obtained.

Mode IV

Diode D₂  must be  conducting  with SW₄ On E  have opposite polarity to that shown in figure  now the  voltage  V₀= 0  whenSW4 is ON  and  current  1₀ will be  positive  when SW₄ is OFF V₀ will be  negative but current  remains in  same  direction. In this condition power  flows  from load to source and  V₀ = -( E+ L di/dt) exceeds Vs.