dc –dc converter (dc – chopper) - asnil blog · pdf file06.04.2009 ·...
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DC – DC CONVERTER(DC – CHOPPER)
ASNILELEKTRO FT UNP
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BLOCK DIAGRAM OF DC‐DC CONVERTERS
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A chopper is a static device which is used to obtain a variable dc voltage from a constant dc voltage source Avariable dc voltage from a constant dc voltage source. A chopper is also known as dc‐to‐dc converter. The thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control Choppers are widely used in trolley carscontrol. Choppers are widely used in trolley cars, battery operated vehicles, traction motor control, control of large number of dc motors, etc….. They are also used in regenerative braking of dc motors to return energy back to supply and also as dc voltage regulatorsenergy back to supply and also as dc voltage regulators.
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Choppers are of two types:Step‐down choppersStep‐up choppers
In step‐down choppers, the output voltage will be less than theinput voltage whereas in step‐up choppers output voltage will bemore than the input voltage.
PRINCIPLE OF STEP‐DOWN CHOPPERPRINCIPLE OF STEP DOWN CHOPPER
V
i0
V
Chopper
+
V V0R
−
Fig. 2.1: Step‐down Chopper with Resistive Load
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Figure 2.1 shows a step‐down 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.
Vdc
v0
V
V/R
i0
Id
ttON tOFF
Idc
tT
Fig. 2.2: Step-down choppers — output voltage and current waveforms
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STEP‐DOWN CHOPPER WITH R‐L LOAD
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CLASSIFICATION OF CHOPPERSChoppers are classified as follows‐ Class A Chopper‐ Class B Chopperpp‐ Class C Chopper‐ Class D Chopper‐ Class E Chopper
CLASS A CHOPPERCLASS A CHOPPER
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CLASS B CHOPPER
Fig. 2.16: Class B Chopper
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CLASS C CHOPPER
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CLASS D CHOPPER
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CLASS E CHOPPER
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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 conductionperiod of the thyristor in each cycleperiod of the thyristor in each cycle.
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