The document provides an overview of DC choppers, detailing their basic principle and operation, along with industrial applications that require variable DC voltage sources. It explains the distinction between AC link choppers and DC choppers, emphasizing the efficiency of choppers that convert fixed DC input to variable DC output. The text concludes with insights gained about the function and types of semiconductor devices used in chopper circuits.

1. Power Electronics - 1 (2150903)
Active Learning Assignment
on
Basic Principle And Operation of DC Chopper
Prepared By:
Patel RajalKumar H.
(160123109013)
Guided By :
Prof. Purv Mistry
Electrical Department
Batch-B3Gandhinagar Institute of Technology 1

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Introduction
Basic principle of DC chopper
Operation of DC chopper
Conclusion
References

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Many industrial application require power from dc voltage
sources. several of these application,. however , perform better
in case these are fed from variable dc voltage sources.
Example of these like trolley buses, subway cars, battery-
operated vehicles, battery-charging etc.
There is two type of chopper
1)AC Link Chopper
2)DC Chopper

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1) AC chopper:
 In the ac link chopper, dc is first converted to ac by an
inverter (dc to ac Converter). AC is then stepped-down or
stepped-up by a transformer which is than converted back to
DC by a diode Rectifier.
 As the conversation is in two stages, dc to ac and then ac to
dc, ac link chopper is costly, bulky and less efficient.

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A chopper is a static device that converts fixed dc input
voltage to a variable dc output voltage directly.
A chopper may be through of as dc equivalent of an ac
transformer since they behave in an identical manner. as
chopper involve one stage conversion. these are more efficient.
The power semiconductor devices used for a chopper circuit
can be power BJT, power MOSFET, GTO or force-
commutated thyristor. These Devices, in general , can be
represented by a switch SW with an arrow as shown in fig (c).

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when the switch is off, on current can flow. when the switch is
on, current flows in the direction of arrow only.
the power semiconductor devices have on-state voltage drops
of 0.5V to 2.5V across them.
As stated above , a Chopper is dc equivalent to an ac
transformer having continuously variable turns ratio, like a
transformer, a chopper can be used to step down or step up the
fixed dc input voltage.

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A chopper is high speed on/off semiconductor switch. it is
connects sources to load and disconnects the load from source
at a fast speed. in this manner, a chopped load voltage as shown
in fig.2(b). is obtained from a constant dc supply of magnitude
Vs Shown in fig.2(a).
Chopper is represented by a switch SW inside a dotted
rectangle, which may be turned-on or turned-off as desired. for
the sake of highlighting the principle of chopper operation, the
circuitry used for controlled on, off periods of this switch is not
shown.

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FIG. 2(a) Elementary chopper circuit

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Fig. 2(b) Output voltage and current waveforms.

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During the period Ton, chopper is on and load voltage is equal to
source voltage Vs. During the interval Toff, chopper is off, load
current flows through the freewheeling diode FD. As a result, load
terminals are short circuited by FD and load voltage is therefore
zero during Toff . in this manner, a chopped dc voltage is produced
at the load terminals. The load current as shown in Fig. 2(b) is
continuous.

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After study this Topic I understand the basic principle and
operation of chopper.
In this topic I studied the Different types of semiconductor are
use as chopper.

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Power Electronics -1
(P.S.Bimbhra)

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