DC DCCONVERTER(DC CHOPPER(DC CHOPPER

ASNILELEKTRO FT UNPELEKTROFTUNP

BLOCK DIAGRAM OF DC DC CONVERTERSBLOCKDIAGRAMOFDCDC CONVERTERS

Achopperisastaticdevicewhichisusedtoobtainavariabledcvoltagefromaconstantdcvoltagesource.Achopperisalsoknownasdctodcconverter.Thethyristor converteroffersgreaterefficiency,fasterresponse lower maintenance smaller size and smoothresponse,lowermaintenance,smallersizeandsmoothcontrol.Choppersarewidelyusedintrolleycars,battery operated vehicles, traction motor control,batteryoperatedvehicles,tractionmotorcontrol,controloflargenumberofdcmotors,etc..Theyarealsousedinregenerativebrakingofdcmotorstoreturnenergybacktosupplyandalsoasdcvoltageregulators.

Choppersareoftwotypes:Stepdownchoppersp ppStepupchoppers

In stepdown choppers, the output voltage will be less than thep pp , p ginput voltage whereas in stepup choppers output voltage will bemore than the input voltage.

PRINCIPLEOFSTEPDOWNCHOPPERChopper

i0

pp

+

V V0R

Fig.2.1:StepdownChopperwithResistiveLoad

Figure 2.1 shows a stepdown chopper with resistive load.The thyristor in the circuit acts as a switch. When thyristor is ON,supply voltage appears across the load and when thyristor is OFF,the voltage across the load will be zero. The output voltage andcurrent waveforms are as shown in figure 2.2.g

v0V

Vdc

ttON tOFF

V/R

i0

Idct

T

Fig. 2.2: Step-down choppers output voltage and current waveforms

STEPDOWNCHOPPERWITHRLLOAD

CLASSIFICATION OF CHOPPERSChoppersareclassifiedasfollowspp ClassAChopper ClassBChopper Class C Chopper ClassCChopper ClassDChopper ClassEChopper

CLASS A CHOPPER

CLASS B CHOPPER

Fig.2.16:ClassBChopper

CLASS C CHOPPER

CLASS D CHOPPER

CLASS E CHOPPER

Exercise

A Chopper circuit is operating on TRC at a

Exercise

A Chopper circuit is operating on TRC at afrequency of 2 kHz on a 460 V supply. If the loadvoltage is 350 volts calculate the conductionvoltage is 350 volts, calculate the conductionperiod of the thyristor in each cycle.