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Module
2
DC Circuit
Version 2 EE IIT, Kharagpur
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View Full Document Lesson
8
Thevenin’s and Norton’s
theorems in the context
of dc voltage and
current sources acting
in a resistive network
Version 2 EE IIT, Kharagpur
Objectives
•
To understand the basic philosophy behind the Thevenin’s theorem and its
application to solve dc circuits.
•
Explain the advantage of Thevenin’s theorem over conventional circuit reduction
techniques in situations where load changes.
•
Maximum power transfer theorem and power transfer efficiency.
•
Use Norton’s theorem for analysis of dc circuits and study the advantage of this
theorem over conventional circuit reduction techniques in situations where load
changes.
L.8.1 Introduction
A simple circuit as shown in fig.8.1 is considered to illustrate the concept of equivalent
circuit and it is always possible to view even a very complicated circuit in terms of much
simpler equivalent source and load circuits. Subsequently the reduction of computational
complexity that involves in solving the current through a branch for different values of
load resistance (
L
R
) is also discussed. In many applications, a network may contain a
variable component or element while other elements in the circuit are kept constant. If the
solution for current (
) or voltage (
V
) or power (
I
P
) in any component of network is
desired, in such cases the whole circuit need to be analyzed each time with the change in
component value. In order to avoid such repeated computation, it is desirable to introduce
a method that will not have to be repeated for each value of variable component. Such
tedious computation burden can be avoided provided the fixed part of such networks
could be converted into a very simple equivalent circuit that represents either in the form
of
practical
voltage
source
known
as
Thevenin’s
voltage
source
(
,
Th
V
magnitude of voltagesource
=
int
Th
Re
r
n
a
l
=
) or in the
form
of
practical
current
source
known
as
Norton’s
current
source
(
,
tan
resis
ce of thesource
N
I
magnitude of current source
=
int
N
r
n
a
l
=
tan
resis
ce
). In
true sense, this conversion will considerably simplify the analysis while the load
resistance changes. Although the conversion technique accomplishes the same goal, it has
certain advantages over the techniques that we have learnt in earlier lessons.
of current source
Let us consider the circuit shown in fig. 8.1(a). Our problem is to find a current
through
L
R
using different techniques; the following observations are made.
Version 2 EE IIT, Kharagpur
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•
Mesh current method needs 3 equations to be solved
•
Node voltage method requires 2 equations to be solved
•
Superposition method requires a complete solution through load resistance (
L
R
)
by considering each independent source at a time and replacing other sources by
their internal source resistances.
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This note was uploaded on 08/03/2010 for the course ELECTRICAL EE212 taught by Professor Shetty during the Spring '10 term at International Institute of Information Technology.
 Spring '10
 shetty
 Volt

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