Circuits 2023
Y.-M. Chen
Circuits
陳 耀 銘 教授
電能處理研究室
(Electric Energy Processing Research Lab. ; EEPro)
電機二館 408；Tel: 3366-3667
E-mail: ntuymchen@ntu.edu.tw
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Circuits 2023
Y.-M. Chen
Textbook
• Engineering Circuit
Analysis
– Twelfth Edition
– by J. David Irwin & R. Mark Nelms
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Circuits 2023
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What can we learn?
• Understand how energy is delivered by
the form of electric power
• Linear electric circuits only
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Circuits 2023
Y.-M. Chen
Grade
Quizzes (3/4) : 60%
Final Exam : 40%
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Circuits 2023
Y.-M. Chen
Class Rules
• 守時不遲到
• 食物要收好
• 專心不睡覺
台灣百合
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Circuits 2023
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Ch1. Basic Concepts
System of Units:
The SI standard system, prefixes
Basic Quantities:
Charge, current, voltage, power and energy
Circuit elements:
Dependent and independent sources
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Circuits 2023
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• SI base units and prefixes
https://physics.nist.gov/cuu/Units/units.html
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Circuits 2023
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• Charge (電荷)
– Amount: Coulomb; C
– Polarity: positive (+) or negative (-)
– electron: qe= -1.6 x 10-19 C
– proton: qp= 1.6 x 10-19 C
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Circuits 2023
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• Current
– the flow rate of charge; the arrow gives the
reference direction of flow
Δq
i=
Δt
1C
1A =
1s
Coulomb
(
) Ampere ; A
sec
dq (t )
instantaneous current : i (t ) =
dt
1 t0 + T
average current : I = iavg =  i (t )  dt
T t0
The direction of a positive current i is the direction
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Circuits 2023
Y.-M. Chen
• Voltage
– the change of potential energy or the potential
difference
dE Joule
v=
(
) Volt ; V
dq Coulomb
1J
1V =
1C
plus sign (+ ) : higher potential
minus sign (-) : lower potential
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Circuits 2023
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• Typical magnitudes of current and voltage
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Circuits 2023
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• Electric power
Power: the rate of energy transfer
dE
p=
dt
Electric power
J
( ) Watt; W
s
p = vi
dE dq dE
p = v i =

=
dq dt dt
passive element: p = vi is absorbing (consuming) power
active element: p = vi is supplying (delivering) power
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Circuits 2023
Y.-M. Chen
• Conservation of energy
Tellegen’s theorem (1952)
₋ The sum of the powers absorbed by all elements in an
electrical network is zero.
₋ Can be used to check calculations when analyzing
electrical networks.
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• Passive Element: energy-absorbing
– Current goes into positive end
• Active element: energy-supplying
– Current goes out of positive end
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• Active elements
– voltage sources
DC: Direct Current
– current source
AC: Alternating Current
DC voltage source vs. AC voltage source
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• Active elements
Sources can be classified as
(A) independent sources
(B) dependent (controlled) sources
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Example 1.7
P2 A = (6)(−2) = −12 W
P1 = (6)(IO ) = 6 IO W
P2 = (12)(−9) = −108 W
P3 = (10)(−3) = −30 W
P4V = (4)(−8) = −32 W
PDS = (8 I x )(11) = (16)(11) = 176 W
Applying Tellegen’s theorem yields
−12 + 6 IO − 108 − 30 − 32 + 176 = 0
Hence, IO = 1A
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Summary
• Know the standard SI units and prefixes.
• Understand the meaning of current, voltage, power,
sources.
• Be able to use power conservation to analyze or verify
simple circuit problems.
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