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Chapter 7
Series-Parallel
Circuits
Introductory Circuit Analysis, 12/e
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OBJECTIVES
• Learn about the unique characteristics of
series-parallel configurations and how to
solve for the voltage, current, or power to
any individual element or combination of
elements.
• Become familiar with the voltage divider
supply and the conditions needed to use it
effectively.
• Learn how to use a potentiometer to
control the voltage across any given load.
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INTRODUCTION
• A series-parallel configuration is
one that is formed by a
combination of series and parallel
elements.
• A complex configuration is one in
which none of the elements are in
series or parallel.
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SERIES-PARALLEL NETWORKS
FIG. 7.1 Series-parallel dc network.
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REDUCE AND RETURN APPROACH
FIG. 7.2 Introducing the reduce
and return approach.
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REDUCE AND RETURN APPROACH
FIG. 7.3 Series-parallel network for
Example 7.1.
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FIG. 7.4 Substituting the parallel
equivalent resistance for resistors R2
and R3 in Fig. 7.3.
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REDUCE AND RETURN APPROACH
FIG. 7.5 Series-parallel network for
Example 7.2.
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FIG. 7.6 Schematic representation of the
network in Fig. 7.5 after substituting the
equivalent resistance R for the parallel
combination of R2 and R3.
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REDUCE AND RETURN APPROACH
FIG. 7.7 Inserting an ammeter and a voltmeter to measure I4 and V2,
respectively.
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BLOCK DIAGRAM APPROACH
• Once the grouping of elements
reveals the most direct approach, you
can examine the impact of the
individual components in each group.
• This grouping of elements is called
the block diagram approach
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BLOCK DIAGRAM APPROACH
FIG. 7.8 Introducing the block diagram
approach.
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FIG. 7.9 Block diagram format of
Fig. 7.3.
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BLOCK DIAGRAM APPROACH
FIG. 7.10 Example 7.3.
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FIG. 7.11 Reduced equivalent of
Fig. 7.10.
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BLOCK DIAGRAM APPROACH
FIG. 7.12 Example 7.4.
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BLOCK DIAGRAM APPROACH
FIG. 7.13 Reduced equivalent of Fig. 7.12.
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DESCRIPTIVE EXAMPLES
FIG. 7.14 Example 7.5.
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FIG. 7.15 Block diagram of Fig. 7.14.
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DESCRIPTIVE EXAMPLES
FIG. 7.16 Alternative block diagram for
the first parallel branch in Fig. 7.14.
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DESCRIPTIVE EXAMPLES
FIG. 7.17 Example 7.6.
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DESCRIPTIVE EXAMPLES
FIG. 7.18 Block diagram for
Fig. 7.17.
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FIG. 7.19 Reduced form of
Fig. 7.17.
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DESCRIPTIVE EXAMPLES
FIG. 7.20 Example 7.7.
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DESCRIPTIVE EXAMPLES
FIG. 7.21 Network in Fig. 7.20 redrawn.
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DESCRIPTIVE EXAMPLES
FIG. 7.22 Example 7.8.
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DESCRIPTIVE EXAMPLES
FIG. 7.23 Network in Fig. 7.22 redrawn.
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DESCRIPTIVE EXAMPLES
FIG. 7.24 Example 7.9.
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FIG. 7.25 Determining VC for
the network in Fig. 7.24.
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DESCRIPTIVE EXAMPLES
FIG. 7.26 Example 7.10.
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DESCRIPTIVE EXAMPLES
FIG. 7.27 Network in Fig. 7.26 redrawn.
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DESCRIPTIVE EXAMPLES
FIG. 7.28 An alternative approach to Example 7.10.
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DESCRIPTIVE EXAMPLES
FIG. 7.29 Example 7.11.
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FIG. 7.30 Network in Fig. 7.29 redrawn
to better define a path toward the
desired unknowns.
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DESCRIPTIVE EXAMPLES
FIG. 7.31 Complex network for Example 7.11.
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LADDER NETWORKS
• A three-section ladder network appears in Fig.
7.32.
• The reason for the terminology is quite obvious for
the repetitive structure.
• Basically two approaches are used to solve
networks of this type.
FIG. 7.32 Ladder network.
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LADDER NETWORKS
FIG. 7.33 Working back to the source to determine RT for the network in Fig. 7.32.
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LADDER NETWORKS
FIG. 7.34 Calculating RT and Is.
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FIG. 7.35 Working back toward I6.
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LADDER NETWORKS
FIG. 7.36 Calculating I6.
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LADDER NETWORKS
FIG. 7.37 An alternative approach for ladder networks.
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VOLTAGE DIVIDER SUPPLY
(UNLOADED AND LOADED)
• When the term loaded is used to describe
voltage divider supply, it refers to the
application of an element, network, or
system to a supply that draws current from
the supply.
– In other words, the loading down of a system
is the process of introducing elements that
will draw current from the system. The
heavier the current, the greater is the
loading effect.
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VOLTAGE DIVIDER SUPPLY
(UNLOADED AND LOADED)
No-Load Conditions
• Through a voltage
divider network
such as that in Fig.
7.38, a number of
different terminal
voltages can be
made available
from a single
supply.
FIG.7.38 Voltage divider supply.
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VOLTAGE DIVIDER SUPPLY
(UNLOADED AND LOADED)
No-Load Conditions
• In general, for a voltage divider
supply to be effective, the applied
resistive loads should be
significantly larger than the
resistors appearing in the voltage
divider network.
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VOLTAGE DIVIDER SUPPLY
(UNLOADED AND LOADED)
Loaded Conditions
FIG. 7.39 Voltage divider supply with loads equal to the average value of the
resistive elements that make up the supply.
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VOLTAGE DIVIDER SUPPLY
(UNLOADED AND LOADED)
Loaded Conditions
FIG. 7.40 Voltage divider supply for Example 7.12.
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POTENTIOMETER LOADING
• For the unloaded
potentiometer in
Fig. 7.41, the
output voltage is
determined by the
voltage divider
rule, with RT in the
figure representing
the total resistance
of the
potentiometer.
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FIG. 7.41 Unloaded
potentiometer.
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POTENTIOMETER LOADING
FIG. 7.42 Loaded potentiometer.
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POTENTIOMETER LOADING
• In general, when hooking up a load
to a potentiometer, be sure that the
load resistance far exceeds the
maximum terminal resistance of
the potentiometer if good control
of the output voltage is desired.
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POTENTIOMETER LOADING
FIG. 7.43 Loaded potentiometer with
RL << RT.
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FIG. 7.44 Loaded potentiometer with
RL >> RT.
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POTENTIOMETER LOADING
FIG. 7.45 Example 7.13.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
FIG. 7.46 Iron-vane movement.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
FIG. 7.48 Basic ammeter.
FIG. 7.47 Iron-vane movement; (a)
photo, (b) symbol and ratings.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
FIG. 7.49 Multirange ammeter.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
FIG. 7.50 Basic voltmeter.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
The Voltmeter
• A variation in the additional circuitry permits
the use of the iron-vane movement in the
design of a voltmeter.
• The 1 mA, 43 Ω movement can also be
rated as a 43 mV (1 mA x 43 Ω), 43
movement, indicating that the maximum
voltage that the movement can measure
independently is 43 mV.
• The millivolt rating is sometimes referred to
as the voltage sensitivity (VS).
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
The Voltmeter
FIG. 7.51 Multirange voltmeter.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
The Ohmmeter
• In general, ohmmeters are designed
to measure resistance in the low,
middle, or high range.
• The most common is the series
ohmmeter, designed to read
resistance levels in the midrange.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
The Ohmmeter
FIG. 7.52 Series ohmmeter.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
The Ohmmeter
FIG. 7.53 Nanovoltmeter.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
The Ohmmeter
• The megohmmeter (often called a
megger) is an instrument for measuring
very high resistance values.
• Its primary function is to test the insulation
found in power transmission systems,
electrical machinery, transformers, and so
on.
To measure the high-resistance values, a
high dc voltage is established by a handdriven generator.
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AMMETER, VOLTMETER, AND
OHMMETER DESIGN
The Ohmmeter
FIG. 7.54 Megohmmeter.
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APPLICATIONS
Boosting a Car Battery
FIG. 7.55 Boosting a car battery.
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APPLICATIONS
Boosting a Car Battery
FIG. 7.56 Current levels at starting.
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APPLICATIONS
Boosting a Car Battery
FIG. 7.57 Current levels if the booster battery is improperly connected.
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APPLICATIONS
Electronic Circuits
• The operation of most electronic systems
requires a distribution of dc voltages
throughout the design.
• Although a full explanation of why the dc
level is required (since it is an ac signal to
be amplified) will have to wait for the
introductory courses in electronic circuits,
the dc analysis will proceed in much the
same manner as described in this chapter.
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APPLICATIONS
Electronic Circuits
FIG. 7.58 The dc bias levels of a transistor amplifier.
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COMPUTER ANALYSIS
PSpice
FIG. 7.59 Using PSpice to verify the results of Example
7.12.
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