14 March 2017

Working of Step up Chopper

Step up Chopper

  • The step up chopper is one in which output DC voltage is greater than the input DC voltage.  
  • The basic diagram for the step up chopper is shown in the figure A.
  •  When the chopper is switched ON during TON time, the energy stored in the inductor via path Vdc – L – CH – Vdc
  • 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 TOFF time, the current passing through inductor is zero and voltage across inductor is L ( di/dt ). 
  • The stored energy of inductor is transferred to the load. 
  • The circuit diagram of step up chopper during chopper OFF time is shown in the figure C.
  • The load / output voltage is equal to

VO = Vdc + VL
     = Vdc + L (di/dt)
  • When chopper is switch ON, the energy stored in the inductor is

Wi = Vdc I TON.......................(1)
  • When chopper is switched OFF, the energy stored in the inductor is transferred to the load.

Wo = ( Vo – Vdc )I TOFF.........(2)
  • If there are no losses in the system, the input energy is equal to output energy

Vdc I TON = ( Vo – Vdc )I TOFF
  Vdc TON = Vo TOFF  – Vdc TOFF
Vdc ( TON + TOFF ) = Vo TOFF
Vo  = [ ( TON + TOFF ) / TOFF ] Vdc
Vo  = [ T / TOFF ] Vdc
OR
Vo  = [ T / ( T –TON ) ] Vdc
Vo  = [ 1 / ( 1 – TON / T ) ] Vdc
Vo  = [ 1 / ( 1 – K ) ] Vdc
When K = 0 ( chopper is in OFF condition )
        Vo  =  Vdc
When K = 1 ( chopper is in OFF condition )
        Vo  =  
  • When the duty cycle lies is in the range of 0 < K < 1, the output voltage lies is in the range of Vdc < Vo < ∞.

Application of DC Step up Chopper


  • The application of step up chopper is in the regenerative braking of DC Motor
  • The output voltage is greater than the input voltage therefore the DC Motor works as DC generator and load current flows from load to supply side.

     working of step up chopper

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