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This chapter covers the analysis of resistive networks using Kirchhoff's Current Law (KCL), nodal analysis, mesh analysis, Thevenin's theorem, Norton's theorem, and the principles of superposition. It also explores the effects of source loading and includes practical examples.
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3 C H A P T E R Resistive Network Analysis
By KCL : i – i – i = 0. In the node 1 2 3 voltage method, we express KCL by v – v v – v v – v a b b c b d – – = 0 R R R 2 1 3 R R v 1 3 b v v a d i i i 1 2 3 R 2 v c Figure 3.2 Use of KCL in nodal analysis
Node a Node b R 2 i R R 1 3 S Node c v v a b R 2 i i 2 i 1 i 3 S i R R 1 3 S v = 0 c Figure 3.3 Illustration of nodal analysis
Node 1 R 3 R 2 R R 1 4 I I 2 1 Node 2 R 3 R 2 R R 4 1 I I 2 1 Figure 3.5
v v v R R a b c 1 3 + v R R i _ S 2 4 S Figure 3.8 Nodal analysis with voltage sources
R R 1 3 + _ v i R i R 1 2 S 2 4 Figure 3.12 A two-mesh circuit
Mesh 1: KVL requires that i R v v v v , – – = 0, where = 1 S 1 2 1 1 v ) R . i – i = ( 2 1 2 1 R R 3 1 + – v 1 + + v _ i v i R R 2 S 1 2 2 4 – Figure 3.13 Assignment of currents and voltages around mesh 1
Mesh 2: KVL requires that v + v + v = 0 2 3 4 where v = ( i – i ) R , 2 2 1 2 v = i R , 3 2 3 v = i R 4 2 4 R R 1 3 + – v 3 – + + v i R v i R v _ S 1 2 2 4 2 4 + – Figure 3.14 Assignment of currents and voltages around mesh 3
5 2 + 10 V 2 A 4 + v _ i x i 1 2 – Figure 3.18 Mesh analysis with current sources
+ + _ _ = + v v B 2 B 2 R R R i i i B 1 B 2 + + _ _ v v B 1 B 1 The net current through R is the sum of the in- dividual source currents: . i + i = i B 1 2 B Figure 3.26 The principle of superposition
1.In order to set a voltage source equal to zero, we replace it with a short circuit. R R 1 1 + v i R i R _ S S S 2 2 A circuit The same circuit with v = 0 S 2. In order to set a current source equal tozero, we replace it with an open circuit. R R 1 1 + + v i v R R _ _ S S S 2 2 A circuit The same circuit with i = 0 S Figure 3.27 Zeroing voltage and current sources
i + Linear v network – i Figure 3.28 One-port network
i + + v v R R R _ S 1 2 3 – Source Load Figure 3.29 Illustration of equivalent-circuit concept
Figure 3.31 Illustration of Thevenin theorum i i R T + + + Load Source Load v v v _ T – –
i i Load Load + + Source i R v v N N – – – Figure 3.32 Illustration of Norton theorum
R 3 a R R 1 2 b R 3 a || R R R 2 1 T b Figure 3.34 Equivalent resistance seen by the load
What is the total resistance the i current will encounter in flowing S around the circuit? R a 3 + R R v i x S 1 2 – b R 3 R R i i 1 2 S S R = R || R + R T 1 2 3 Figure 3.35 An alternative method of determining the Thevenin resistance
R R 3 1 i L + v R R S 2 _ L Figure 3.46
R R 3 1 + + v v O C S R 2 _ – Figure 3.47
R R 1 3 + – + 0 V + + v R v v O C 2 O C S _ – – i Figure 3.48
R R R + R || R 1 3 3 1 2 i i L L R + + v R v R 2 R _ _ S 2 S L L R + R 1 2 A circuit Its Th é venin equivalent Figure 3.49 A circuit and its Thevenin equivalent
One-port i SC network i R = R i SC N T N Figure 3.57 Illustration of Norton equivalent circuit
Short circuit replacing the load v R R 3 1 R i + v 2 S S C _ i i 1 2 Figure 3.58 Computation of Norton current
R T One-port v + i R T network N T _ Th é venin equivalent Nortonequivalent Figure 3.63 Equivalence of Thevenin and Norton representations
R R 1 3 + v R i _ S 2 SC R 3 v S i R R 1 2 SC R 1 Figure 3.64 Effect of source transformation
Node a a a a R + or or R i i R v _ S S S + v _ S b b b Node b The venin subcircuits é Norton subcircuits Figure 3.65 Subcircuits amenable to source transformation
a Unknown Load network b An unknown network connected to a load a A Unknown network i “ ” r SC m b Network connected for measurement of short- circuit current a + Unknown V v r “ ” network m O C – b Network connected for measurement of open- circuit voltage Figure 3.71 Measurement of open-circuit voltage and short-circuit current
Practical source R L Load R T + v R _ T L i L Source equivalent , what value of Given v and R R T T L will allow for maximum power transfer? Figure 3.73 Power transfer between source and load
v + – i n t R T + v R _ T L i Source Load i + i n t i v R R N L T – Source Load Figure 3.74 Source loading effects
Nonlinear element as a load. We wish to solve for v and i . x x R T i x + Nonlinear + v v _ x element T – Figeure 3.77 Representation of nonlinear element in a linear circuit
i X v T v 1 T R Load-line equation: i = – v + T x R R x T T – 1 R T v v T x Figure 3.78 Load line
i x curve of i-v “ exponential resistor ” v T R v T i = I e , v > 0 o Solution v 1 T Load-line equation: i = v + x x R R T T v v T x Figure 3.79 Graphical solution equations 3.48 and 3.49
R T i i x x + + Linear Nonlinear + Nonlinear v v v network _ x load x load T – – Figure 3.80 Transformation of nonlinear circuit of Thevenin equivalent