electrical engineering: principles and applications, fourth edition, by allan r. hambley, 2008...

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Lecture 3Circuit Laws,

Voltage & Current Dividers


KIRCHHOFF’S CURRENT LAW

• The net current entering a node is zero.

• Alternatively, the sum of the currents entering a node equals the sum of the currents leaving a node.


KIRCHHOFF’S VOLTAGE LAW

The algebraic sum of the voltages equals zero for any closed path (loop) in an electrical circuit.


Using KVL, KCL, and Ohm’s Law to Solve a Circuit


A 3 5V 15

yi

yxx iii 5.0

A 2xi


V 2010 xx iv

15 xs vV

V 35sV

A 2xi


Chapter 2 Resistive Circuits

1. Solve circuits (i.e., find currents and voltages of interest) by combining resistances in series and parallel.

2. Apply the voltage-division and current-division principles.

3. Solve circuits by the node-voltage technique.


4. Solve circuits by the mesh-current technique.

5. Find Thévenin and Norton equivalents and apply source transformations.

6. Apply the superposition principle.

7. Draw the circuit diagram and state the principles of operation for the Wheatstone bridge.


eqiRRRRiiRiRiRvvvv )( 321321321


eqRv

RRRv

Rv

Rv

Rviiii

321321321

111


163

62

61

21

31

611111

432

RRRReq


1

311RRtotal


21

63

61

62

61

311

eqR

0.2eqR


1.5

1028eqR


5102

101

1011

eqeq

RR


Circuit Analysis using Series/Parallel Equivalents

1. Begin by locating a combination of resistances that are in series or parallel. Often the place to start is farthest from the source.

2. Redraw the circuit with the equivalent resistance for the combination found in step 1.


3. Repeat steps 1 and 2 until the circuit is reduced as far as possible. Often (but not always) we end up with a single source and a single resistance.

4. Solve for the currents and voltages in the final equivalent circuit.


VAiRv

AVRv

i

AVRv

i

30310

16060

23060

111

3

23

2

22


Voltage Division

total321

111 v

RRRRiRv

total321

222 v

RRRRiRv

Of the total voltage, the fraction that appears across a given resistance in a series circuit is the ratio of the given resistance to the total series resistance.


Application of the Voltage-Division

Principle

V5.1

156000200010001000

1000

total4321

11

v

RRRRRv


totaltotaleqeq iRR

RRiRv

RRRR

R21

21

21

21


Current Division

total21

2

11 i

RRR

Rvi

total21

1

22 i

RRR

Rvi

For two resistances in parallel, the fraction of the total current flowing in a resistance is the ratio of the other resistance to the sum of the two resistances.


AiRR

Ri

ARR

vi

s

x

ss

417.025.16030

30

25.12060

100

32

23

1

Find i3


Find i1


Application of the Current-Division

Principle

A10152010

20

eq1

eq1

siRR

Ri

2060306030

32

32eq RR

RRR


Use the voltage division principle to find the unknown voltages


VVVvRRRR

Rv

VVVvRRRR

Rv

VVVvRRRR

Rv

VVVvRRRR

Rv

s

s

s

s

602

1201203015105

304

304

1201203015105

15

206

1201203015105

10

1012

1201203015105

5

43214

4321

33

4321

22

4321

11


92.2

51

71

1eqR

VVVvRRR

Rv

VVVvRRR

Rv

VVVvRRR

Rv

seq

seq

eq

seq

06.892.920420

492.234

89.592.92092.220

492.2392.2

05.692.920320

492.233

41

44

412

41

11


Use the current division principle to find the currents


AiRRR

RRi

AiRRR

Ri

t

t

23152010

30

13152010

15

321

213

321

31


5

101

101

1

eqR

AiRR

Ri

AiRR

Ri

AiRR

Ri

seq

eq

seq

eq

seq

eq

13105

5

13105

5

13105

5

13

12

11


Resistor Cube

electrical engineering: principles and applications, fourth edition, by allan r. hambley, 2008...

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