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What is a Thevenin Equivalent Circuit?
Figure 1 shows a circuit that has been separated into two parts, Circuit A and Circuit B. These
parts are connected at a single pair of terminals.
Figure 1.
Two circuits connected at a pair of terminals.
We’d like to understand the interaction between these two circuits. Circuit A and Circuit B share
two things: the current,
i
, and the voltage,
v
. It seems reasonable to ask
1.
Are
i
and
v
related to each other? If so, how?
2.
Does Circuit B affect
i
and
v
? How?
3.
Suppose we knew
i
and
v
. What would they tell us about Circuit A?
To start our investigation, let’s simply the problem by considering the case where Circuit B is a
single resistor:
Figure 2.
Circuit B is a resistor.
Let’s go to the laboratory and take some data:
R
,
Ω
1
2
3
4
5
6
8
10
15
i
, A
0.476
0.455
0.435
0.417
0.400
0.385
0.357
0.333
0.286
v
, V
0.476
0.909
1.304
1.667
2.000
2.308
2.857
3.333
4.286
R
,
Ω
20
25
30
40
50
100
i
, A
0.250
0.222
0.200
0.167
0.143
0.083
v
, V
5.000
5.556
6.000
6.667
7.143
8.333
(This data was obtained by computer simulation using PSpice [] rather than laboratory
measurements. The circuit labeled “Circuit A2” in Figure 10 was used as Circuit A.)
1
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View Full Document Maybe a picture will help us to see a pattern in this data. Figure 3 shows a graph of
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This note was uploaded on 05/10/2008 for the course EEL 3004 taught by Professor Gong during the Spring '08 term at University of Central Florida.
 Spring '08
 gong

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