11 March 2017

Working Principle of DC Chopper

Function of DC Chopper

  • The function of the DC chopper is to convert fixed DC into variable DC. A DC chopper is connected between supply source and load. 
  • The variable output voltage is obtained by switching on and off SCR at regular interval. 
  • The on and off time of the SCR is in the micro second.
  • When the SCR is switched ON during TON time, the output voltage across load is Vdc
  • The output voltage across load becomes zero when the SCR is switched OFF during TOFF time. 

working-principle-of-dc-chopper

  • The average output voltage across load depends upon switching time  ( Turn on time + Turn off time ) of the SCR.

VO = ( TON / TON + TOFF ) Vdc
                                  = ( TON / T  ) Vdc
               = K Vdc
      Where VO = Output voltage
                          Vdc = Input voltage
                         TON = Chopper on time
                        TOFF = Chopper off time
                               T = Chopper time period
                              K = Duty cycle
                          If K > 1, Step up chopper
                              K < 1, Step down chopper
  • The DC chopper works as DC transformer and variation of output voltage is obtained by duty cycle.

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