Power electronics digital notes b. Tech III year

 
Figure: 3.14 circuit diagram and quadrant operation of Type C chopper 
 
 
Figure: 3.15 Output voltage and current waveforms of type C chopper 
Class D chopper 
• Class D is a two quadrant chopper.
• When both CH1 and CH2 are triggered simultaneously, the output voltage vO = V and output current 
flows through the load. 
• When CH1 and CH2 are turned OFF, the load current continues to flow in the same direct
ion through 
load, D1 and D2 , due to the energy stored in the inductor L. 

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• Output voltage vO = –
V. 
• Average load voltage is positive if chopper ON time is more than the OFF time
• Average output voltage becomes negative if tON < tOFF .
• Hence the direc
tion of load current is always positive but load voltage can be positive or negative. 
Figure: 3.16 circuit diagram and quadrant operation of Type D chopper 
Figure: 3.17 Output voltage and current waveforms of type D chopper 

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Class E Chopper 
• Class E 
is a four quadrant chopper 
• When CH1 and CH4 are triggered, output current iO flows in positive direction through CH1 and CH4, 
and with output voltage vO = V. 
• This gives the first quadrant operation.
• When both CH1 and CH4 are OFF, the energy stored in
the inductor L drives iO through D2 and D3 in 
the same direction, but output voltage vO = -V. 
• Therefore the chopper operates in the fourth quadrant.
• When CH2 and CH3 are triggered, the load current iO flows in opposite direction & output voltage vO 
= -V. 
• Since both iO and vO are negative, the chopper operates in third quadrant.
• When both CH2 and CH3 are OFF, the load current iO continues to flow in the same direction D1 and 
D4 and the output voltage vO = V. 
• Therefore the chopper operates in secon
d quadrant as vO is positive but iO is negative.