15 March 2017

Type A Chopper ( Class A chopper )

  • The power circuit diagram of the type A chopper is shown in the figure A. 
  • The commutation circuit is not shown in this figure A. 
  • When chopper CH1 is switched on, the load current flow through path VDC – CH1 – A – L – B – LAOD – C – D – VDC
  • The output voltage in this condition is VDC. The energy stored in the inductor during this time period. 
  • When chopper CH1 is switched off, the output voltage becomes zero and stored energy of inductor dissipates through L – B – LOAD – C – D – A path.
  • The load current and load voltage both are positive and power flows from supply to load side. 
  • This type of chopper is called as step down chopper because the output voltage is less than the input voltage. 
  • The output voltage and current waveform are shown in the figure B.

Discontinuous current

  • When the chopper on time is less than off time, the load current increases exponentially during chopper on time and it become zero during chopper off time. This is called as discontinuous current.
                                          TON < TOFF

Continuous current

  • When the chopper on time is greater than the off time, the load current flows continuously. The load current increases exponentially during chopper on time and decreases during chopper off time. 
  • The chopper is switched on again before the current becomes zero.
                                         TON > TOFF 

working of type a chopper