Step up / Step down Chopper

Working of Step up / 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)

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

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

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