20 March 2017

Type D Chopper ( Class D Chopper )

  • The two quadrant type B chopper or type D chopper is shown in the figure A. 
  • This chopper works in first as well as fourth quadrant therefore the output current remain positive but output voltage may be either positive or negative. 
  • The polarity of output voltage depends upon chopper ON time and chopper OFF time. When
             TON > TOFF – Output voltage positive
             TON < TOFF – Output current negative
             TON = TOFF – Output voltage zero

First quadrant

  • When chopper CH1 and CH2 both are switched on simultaneously, the current flows through path (+)Vdc – A – CH1 – B – LOAD – CH2 – Vdc( – ). 
  • The voltage across load is equal to Vdc and current increases exponentially. 
  • The chopper works in first quadrant because the output voltage and output current both are positive.

Fourth quadrant

  • When chopper CH1 and CH2 both are switched off simultaneously, the diode D1 and D2 forward biased and current flows through path B – LOAD – D2 – D –  (+)Vdc  – Vdc( – ) – C – D1 – B. 
  • The chopper works in fourth quadrant because the output voltage negative and output current positive becomes positive.
  • The application of type D chopper is in the forward motoring and regenerative braking of motor. The output voltage and current waveform is shown in the figure B.

type d chopper
              working of type d chopper
waveform of type d chopper
waveform of type d chopper


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