19 March 2017

Type C Chopper ( Class C Chopper )

  • The type C chopper is parallel combination of type A and type B chopper. The output voltage is always positive but output current either positive or negative in this type of chopper therefore it works in first as well as second quadrant.
CH1 and CH2 OFF
  • The diode D1 and D2 does not forward biased because of CH1 and CH2 remain off at starting condition. 
  • The load is completely isolated from the supply system.
Diode D1 / Chopper CH2 Conducts
  • The output voltage becomes zero when diode D1 or CH2 conducts. 
  • The output voltage becomes VDC When diode D2 or chopper CH1 conducts.


Conduction
Output voltage
Diode D1 / chopper CH2
Zero
Diode D2 / chopper CH1
VDC

  •  The waveforms for gate signal G1, gate signal G2, output current and output voltage is shown in the figure C. 
  • The chopper CH1 is switched on at point A and load current flows from supply to load side. 
  • The inductor current increases exponentially. 
  • The chopper CH1 is switched off at point B and load current flows through path L – LOAD – D1 – L. 
  • When the value of L(di/dt) is equal to back emf Eb, the load current becomes zero ( Point C ). 
  • The diode D1 conducts during point B to point C.
  • The chopper CH2 is switched on at point C due to back emf of the DC motor. 
  • The load current flows in the negative direction through path LOAD – L – CH2 – LOAD. 
  • The negative current flows continue until chopper CH2 is switched and chopper CH1 is switched on ( Point D ).
  •  When the chopper CH2 is switched off, the stored energy of inductor dissipated its energy through path L – D2 – VDC – LOAD – L. 
  • The chopper CH1 remains off in spite of it receives gate signal. The chopper CH1 switched on at point E where the negative current becomes zero.
Chopper CH1 / Diode D1 Conducts
  • When chopper CH1 or diode D1 conducts, the load current becomes positive and load current becomes negative when CH2 or D2 conducts. The chopper CH1 and CH2 never conducts simultaneously otherwise the DC supply source is short circuited.

working of type c chopper
working of type c chopper

working of type c chopper
waveforms of the type c chopper



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