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Unit 1: Basic Circuit Theory
Unit 1.4: Circuits and Circuit Elements
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Circuits and Circuit Elements
f
In this lecture,
you will learn about:
±
Representing physical systems as circuit
diagrams
±
Conventional Symbols used in circuits
• Ideal voltage and current sources
• Resistors
• Practical Voltage Source
• Others
• Dependent Sources
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Physical System Example
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Physical System Example #2
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Schematic of Physical System
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Schematic of Physical System
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AC and DC
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DC:
Direct Current
±
Electrical current that flows in one direction
only.
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AC:
Alternating Current
±
Electrical current that changes (or alternates)
in magnitude and direction at regular intervals.
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These terms are also applied to voltages:
±
DC voltage or AC voltage
• Direct Current Voltage may seem weird, but that’s
the way it is.
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These terms are also applied to sources:
±
DC current source or AC voltage source, etc.
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EE302: DC Circuit Analysis
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Nomenclature: lower case i, v denote
general representations for current
and voltage that may be DC and/or
AC
f
For EE302, we will focus on DC
circuits
±
I (upper case) will denote currents
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V (upper case) will denote voltages
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Types of Devices
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Active Devices
±
Capable of generating power
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Examples: voltage and current sources,
operational amplifiers, transistors
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Passive Devices
±
Cannot generate power
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Examples: resistors, capacitors,
inductors
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For EE302, we focus on DC circuits
involving resistors
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Battery
Æ
Voltage Source
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Source of power
±
Provides voltage (12 V)
±
Provides current
• Varies depending what is
attached to the battery
+

12 V
or
Circuit
Symbol:
+

12 V
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Ideal Voltage Source: Properties
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If providing power to circuit, which way does
the physical current flow?
f
Always provides the
specified voltage between its
terminals.
f
Current determined by the
attached circuit.
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Can supply unlimited power.
+

12 V
a
b
I
I
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Can a voltage source absorb power??
f
Battery Charger
±
The battery being
charged acts as a
load.
±
It absorbs power
from the circuit.
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Ideal Current Source: Properties
f
Always provides the specified
current flowing from b to a.
f
Voltage between a and b can
vary.
f
Can provide unlimited power.
2 A
a
b
No everyday analogy for a current source.
Useful to model more advanced devices.
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Headlight
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Can I represent the
headlight as a voltage or
current source?
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No
±
Gets its power from the
battery
±
Absorbs power all the time
resistor
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Resistor:
Ohm’s Law
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The current through a
resistor and the voltage
across it are proportional.
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This note was uploaded on 08/27/2009 for the course EE 16200 taught by Professor Williamneal during the Fall '08 term at University of Texas at Austin.
 Fall '08
 WilliamNeal
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