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.
  •  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.
  • 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.
  •  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