Electric Circuits
Chapter 1: Circuit Variables
Chapter 2: Circuit Elements
1
Course Contents
Ch. 1. Circuit variables
❑ Ch. 2. Circuit elements
❑ Ch. 3. Simple resistive circuits
❑ Ch. 4. Techniques of circuit analysis
❑ Ch. 5. The operational amplifier
❑ Ch. 6. Inductance, capacitance, and mutual inductance
❑ Ch. 7. Response of first-order RL and RC circuits
❑ Ch. 8. Natural and step response of RLC circuits
❑ Ch. 9. Sinusoidal steady-state analysis
❑ Ch. 10. Sinusoidal steady-state power calculations
❑ Ch. 12. Introduction to the Laplace transform
❑ Ch. 13. The Laplace transform in circuit analysis
❑ Ch. 14. Introduction to frequency selective circuits
❑
2
3
1.1 Electrical Engineering:
An Overview
❑ Electrical & Electronics Systems
▪ Produce, transmit, and measure electric signals
❑ Electrical Systems
▪ Communications systems
▪ Computer systems
▪ Signal-processing systems
▪ Control systems
▪ Power systems
4
Communication Systems
❑ Example:
▪ Television equipment
▪ Satellite systems
▪ Wireless communication systems
– CDMA
▪ ADSL, VDSL
5
Signal-processing systems
Control systems
6
Circuit Theory
❑ Electric circuit is a mathematical model that
approximates the behavior of an actual electrical
system
❑ The goal of circuit analysis is to understand “ideal
circuits” and the constraints imposed on currentvoltage relationship resulting from interconnecting
“ideal elements”
❑ The resulting interconnection (the “circuit”) will
quantitatively (or approximately) predict the behaviors
of the electrical system it is intended to represent.
7
Want to See a Circuit?
8
1.2 International System of Units
9
‰
-
o0
_
10
1.3 Circuit Analysis: An Overview
❑
Circuit model: mathematical model
for electrical systems
❑
Circuit component: elements that
comprise the circuit model
❑
Circuit analysis is based on
mathematical techniques and is
used to predict the behavior of the
circuit model and its ideal circuit
components
❑
Physical prototype: actual
electrical system constructed from
actual electrical components
11
1.4 Voltage and Current
❑ Electric charge
▪ Basis for describing all electrical phenomena
▪ Described in positive and negative charges
▪ Exists in discrete quantities, which are integral multiples of the
electronic charge, 1.6022x10^-19 C
▪ Electrical effects are attributed to both the separation of charge
and charges in motion
❑ Separation of charge creates an electric forces (voltage)
❑ Motion of charge creates an electric fluid (current)
12
Voltage
❑
❑
Whenever positive and negative charges are separated, energy is expended.
Voltage is the energy per unit charge created by the separation
13
Current
❑ Current: the rate of charge flow
14
1.5 Ideal Basic Circuit Element
15
Passive Sign Convention
16
1.6 Power
❑ Power: the rate of energy flow
17
Power Sources
18
The Ideal Basic Circuit Elements
19
Sign Convention
20
21
22
Energy
❑ Energy: the integral of power over time (stored,
dissipated)
23
Summary and Problems
24
25
2.1 Voltage and Current Sources
e 독립적
ε
다르부분의영향을받음
.
26
2.1 Voltage and Current Sources
e
'
independent
❑ Circle is used to represent an independent source
27
Diamond is used to represent
a dependant source.
❑ Dependant sources may be
controlled by either a voltage
or a current elsewhere in the
circuit
❑ Dependant sources are called
controlled sources
❑ Active elements: models a
device capable of generating
electric energy.
❑ Passive elements: model
physical devices that cannot
generate electric energy
❑
"
dependent
∞
28
Example 2.1
a
←
unvalid
.
29
Example 2.2
V
30
㉘
Accessing Objective
ib
= -
8ft
p !
=
ㅁ
-
=
O
P
」
ㆍ같은값
=
=
+ Vi
F ( 2V)
-
=
-
(8A)
16w
31
2.1 Electrical Resistance (Ohm’s Law)
❑
Resistance is the capacity of materials to impede the flow of
current or the flow of electric charge. The circuit element used to
model this behavior is the resistor.
32
Resistive Element
[저항 ]
33
Ohm’s Law
ㅇ
σ
❑
34
Ohm’s Law
V
=
iR
참로만하기
,
Power dissipated in a resistor is p=vi
35
Example 2.3
vo
↓
야
"
↑
↓
it
VC = 20V
-
lor
o
40
r
9 7
칭
36
2.3 Construction of Circuit Model
Short circuit: R=0
❑ Open circuit: R=
❑
37
2.4 Kirchhoff’s Laws
□
목
(
만나는지점
"
i
Fin
i . tzti
,
=
0
dis
38
Example
-
5A
-
A
5
대렸이 D
그
iitkt.
39
Kirchhoff’s Current Law
늙잃
들어오는것 보단 나라는 것을 보름 기준으로함
i ne o √
=
-
-
O
O
o
istil o
js
=
-
2(
=
-
σ
0
% ,ti o
=
4개의 node
√
σ
방향에따라 t )붙이기
Kl
40
Closed Path or Loop
폐도선
.
Da중첩
'
1 p에서의 V의 합미 임
"
.0
41
Kirchhoff’s Voltage Law (KVL)
진출점 진업점에 대한 부호고정
ㅇ
,
ㅇ
θ
ㅇ
42
ㅇ
ㅇ
ㅇ
℃
43
Example 2.6:
Using Kirchhoff’s Current Law
←
node가 없다면 만나지X
행 ☆
44
.
Example 2.7:
Using Kirchhoff’s Voltage Law
⑦
ㅇ
□
ㅇ
θ
ㅇ
ㅇ
ㅇ
□
□
ㅇ
ㅇ
ㅇ
□
45
2.5. Analysis of a Circuit
Containing Dependent Sources
5io
θ
ㅇ
← 5io
.
zo
^
‰
σ
iof5io 일 0
=
.
. bio
=
KcL
_
-
500 +5 io +20i =①
.
.v.
46
❑
Apply Kirchhoff’s voltage law around the 1st close path
Apply Kirchhoff’s voltage law around the 2nd close path, but we fail
to develop a useful equation, because we don’t know the voltage
value across the dependent current source.
❑ Apply the Kirchhoff’s current law. We select node b.
❑
47
Example 2.10
❑ Applying Ohm’s Law and Kirchhoff’s Laws to find an
unknown voltage
p
=-
=
Vsins
-
=1 6n
+ 20
16 nW
.
-
.
0
-
A : is
1ot 6is
0
=
‰
-
gis + ai + 3.
.
=
0
48
Summary
EX) 2 8
.
+
10일
.
107
b
-
Tnovn
→
*
ㆁ
502
:
50is
애
'
_
a
kcl cnodeb ) :
KV ( ( loopa)
-
-
호 ti
.
-
.
6
=
0
120 + l 0i t 50i
0
49
Problems
Vb VAtVR
=
한 * " iin}
+
_
P= V 일
=R
=
2
VEIER
VERVEER
Paats
paevin
=
iR
=
i2 .
"
=
*
=
Loop이 있는지 , node가 엉디에 있는지
변수에 대한 정부얻기
β
p vo
=잊R
=
R
=
-
~
붚회
Vs
VR
+
_
V= ER
b
*
=
환
{
"
. ⑤
-
-
a
,
,
50
Next Lecture and Reminders
❑ Next Lecture:
▪ Ch3. Simple Resistive Circuits
51