Working of the Step Up / Step Down Chopper

•  It is a chopper which can work as step up chopper as well as step down chopper. 
• When the chopper is switched ON during T_ON time, the energy stored in the inductor via path V_dc – CH – L – V_dc.
• The direction of current passing through inductor is shown in the figure B when the chopper CH is switched on. 
• When chopper is switched OFF during T_OFF time, the current passing through inductor is zero and voltage across inductor is L ( di/dt ).  
• As the direction of voltage polarity across inductor changes, the stored energy of inductor dissipates via path L – LOAD – D – L.
• When chopper is switch ON, the energy stored in the inductor is

W_i = V_dc I T_ON.......................(1)

• When chopper is switched OFF, the output energy

W_o = V_oI T_OFF......................(2)

• The input energy is equal to output energy when there are no losses in the system. Therefore from equation ( 1 ) and ( 2 )

               V_dc I T_ON = V_oI T_OFF

                          V_o  = [ T_ON / T_OFF ] V_dc

                                    OR

                       V_o  = [ T_ON / ( T  – T_ON ) ] V_dc

                       V_o  = [ 1 / ( T / T_ON – 1 ) ] V_dc

                       V_o  = [ 1 / ( 1 / K – 1 ) ] V_dc

             Where K = Duty cycle = T_ON / T

                      V_o  = [ K / ( 1 – K )  ] V_dc

The chopper works as step down chopper if 0 < K < 0.5

                      V_o < V_dc  

The chopper works as step up chopper if 0.5 < K < 1

                       V_o > V_dc  

STEP UP / STEP DOWN CHOPPER DRAWING.PDF

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