Type D Chopper ( Class D Chopper )

Working

• 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

             T_ON > T_OFF – Output voltage positive

             T_ON < T_OFF – Output current negative

             T_ON = T_OFF – Output voltage zero

First quadrant

• When chopper CH1 and CH2 both are switched on simultaneously, the current flows through path (+)V_dc – A – CH1 – B – LOAD – CH2 – V_dc( – ). 
• The voltage across load is equal to V_dc 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 –  (+)V_dc  – V_dc( – ) – 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 DRAWING.PDF

TYPE D CHOPPER WAVEFORMS DRAWING.PDF

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