basic concepts dasar rangkaian elektronika (dre)
TRANSCRIPT
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Basic Concepts
Chapter 1
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Ch01_Basic Concepts 2
Chapter 1: Basic Concepts
1. Introduction
2. Systems of Units
3. Charge and Current4. Voltage
5. Power and Energy
6. Circuit Elements
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Ch01_Basic Concepts 3
Introduction
An electric circuit is an interconnection ofcircuit elements
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Ch01_Basic Concepts 4
Complicated Circuits
Electric circuit of a radio receiver.
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Ch01_Basic Concepts 5
System of Units
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Ch01_Basic Concepts 6
Units in Circuit
Physic Term Unit SymbolCharge Coulomb C
Voltage Volt() V(v)
Current Ampere() A
Power Watt W
Energy (Work) Joule J
Resistance Ohm()
Inductance Henry() H
Capacitance Fara() F
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Andre-Maria Ampere (1775-1836)
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Ch01_Basic Concepts 8
Alessandro Antonio Volta
(1745-1827)
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Ch01_Basic Concepts 9
1 A = 10 12A
1A = 10 6A
1nA = 10 9
A
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Ch01_Basic Concepts 10
Charge and Current
Atoms contain electrons An electron carries a negative charge of magnitude
The charge is measured in Coulombs (C).
The charges occurring in nature are integral multiples of
the electron charge
The law of conservation of charge: the charge can neither
be created nor destroyed, but only transferred
1e = 1:602 10 19
C
1C has6:24 1018
electron
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Ch01_Basic Concepts 11
Characteristics of electric charge are: It is bipolar.
It exists in discrete quantities.
Electrical effects are attributed to both theseparation of charge and charges in motion.
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Ch01_Basic Concepts 12
Current
Definition: Electric current is the time rate ofchange of charge, measured in amperes and
expressed as
= current in amperes (A),
= charge in coulombs (C)= time in seconds (s)
So
Also, 1 ampere = 1 coulomb/second
tq
i
dt
dqi
t
ditq )()(
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Ch01_Basic Concepts 13
Electric current due to flow of electronic charge in a conductor.
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Ch01_Basic Concepts 14
Although current is made up of discretemoving electrons, we consider i to be a
continuous variable as there are so many of
them. Thus, current is defined as the rate of flow of
positive charge.
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Ch01_Basic Concepts 15
A direct current(dc) is a current that remainsconstant with time.
An alternating current(ac) is a current that
varies sinusoidally with time.
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Ch01_Basic Concepts 16
Two Common types of current:(a) Direct current (dc).
(b) Alternating current (ac).
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Ch01_Basic Concepts 17
Conventional current flow:
(a) Positive current flow,(b) Negative current flow.
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Ch01_Basic Concepts 18
Example 1.1
Each electron has -1.60210-19 C.
4600 electrons will have
-1.60210-19 4600 = -7.36910-16 C
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Ch01_Basic Concepts 19
Example 1.2
mA41.311002cos102sin5
,5.0At
mA)4cos204sin5(
mC/s)4sin5(
mC4sin5
i
t
ttt
tt
dt
d
dt
dqi
ttq
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Ch01_Basic Concepts 20
Example 1.3
C5.52
11)28(
2
)3(
2
1
23
2
1
22
1
tt
dtttidtQt
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Ch01_Basic Concepts 21
Voltage
Definition: The voltage (potential difference)between two points a and b is the energy (work)
required to move a unit charge from a to b.
= voltage in volts (V),= energy in joules (J)
= charge in coulombs (C)
1 V=1 Joule/Coulomb.
qwv
dqdwvab
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Ch01_Basic Concepts 22
Polarity of voltage vab
.
baab vv
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Ch01_Basic Concepts 23
Two equivalent representations of the same voltage vab:
(a) point a is 9 V above point b,(b) Point b is -9 V above point a.
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Ch01_Basic Concepts 24
Power and Energy
Definition of power: Power is the time rate ofexpending or absorbing energy, expressed as:
= power in watts (W),= energy in joules (J)
= time in seconds (s)t
wp
dt
dwp
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Ch01_Basic Concepts 25
Power is associated with the flow of charge:follows from the definition of voltage and
current
= power in watts (W),
= voltage in volts (V)
= current in amperes (A)t
v
p
vidt
dq
dq
dw
dt
dwp
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Ch01_Basic Concepts 26
p(t)=v(t)i(t); power is usually time-varying and p(t)is called the instantaneous power
A large power does not mean a large energy; only
under a large power with a duration a large energy
can be obtained
t
dptW )()(
Reference Polarity and Reference
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Ch01_Basic Concepts 27
Reference Polarity and Reference
Direction
Polarity reference for voltage (v) Reference direction for current (i)
Assignment of reference polarity forv and
reference direction fori is entirely arbitrary
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Ch01_Basic Concepts 28
Reference polarities for power using the positive sign convention:
(a) absorbing power, (b) supplying power.
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Ch01_Basic Concepts 29
Passive Sign Convention
Definition: Whenever the reference directionfor the current in an element is in the direction
of the reference voltage drop across the
element, use a positive sign in any expressionthat relates the voltage to the current.
Otherwise, use a negative sign.
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Ch01_Basic Concepts 30
Two cases of an element with an absorbing power of 12 W:
(a) P= 43 = 12 W, (b)p = 43 = 12 W.
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Ch01_Basic Concepts 31
A positive power p=vi means that the elementis absorbing (consuming) energy; conversely
an element with a negative power means that it
supplies (provides) energy.
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Ch01_Basic Concepts 32
Figure 1.10
Two cases of an element with a supplying power of 12 W:
(a) P=43 =12 W, (b)p =43 =12 W.
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Ch01_Basic Concepts 33
Power and Energy (II)
Law of conservation of energy: The algebraicsum of power in a circuit, at any time instant,
must be zero:
Total power supplied to a circuit must balance
the total power absorbed.
0 p
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Ch01_Basic Concepts 34
Definition of energy: Energy is the capacity todo work, measured in joules (J).
The energy obtained in the interval [t0, t] is
given by
The electric power utility companies measures
energy in watt-hours (Wh), where:
1Wh = 3600J
dtvipdtwt
t
t
t 00
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Ch01_Basic Concepts 35
1884 Exhibition
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Ch01_Basic Concepts 36
Ideal Basic Circuit Element
Attributes:Has only 2 terminals.
The elements can be divided into thepassive
and the active elements An active element is capable of generating
energy while a passive element is not
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Ch01_Basic Concepts 37
Circuit Elements
Three passive circuit elements are considered:Resistors (R)
Inductors (L)
Capacitors (C) Two active circuit elements are considered:
Voltage source (V)
Current source (I)
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Ch01_Basic Concepts 38
Each source (voltage or current source) isdivided into the independent and the dependent
source.
An independent voltage (current) source is anactive element that provides a specified
voltage (current) which is completely
independent of other circuit variables.
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Ch01_Basic Concepts 39
Symbols for independent voltage sources:
(a) used for constant or time-varying voltage,(b) used for constant voltage (dc).
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Ch01_Basic Concepts 40
Symbol for independent current source.
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Ch01_Basic Concepts 41
Dependent Sources
A dependent (or controlled) source is anactive element in which the source (voltage or
current) quantity is controlled by another
voltage or current in the circuit.
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Ch01_Basic Concepts 42
Symbol for:
(a) dependent voltage source, (b) dependent current source.
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Ch01_Basic Concepts 43
Four types of ideal dependent sources:Voltage-controlled voltage source (VCVS)
Current-controlled voltage source (CCVS)
Voltage-controlled current source (VCCS)
Current-controlled current source (CCCS)
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Ch01_Basic Concepts 44
The source on the right-hand side is a current-controlled
Voltage source.
E l 1 7
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Ch01_Basic Concepts 45
Example 1.7
E l 1 7
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Ch01_Basic Concepts 46
Example 1.7
084860100
W8)52.0(8)2.0(8
W48)6(8
W60)5(12
W100)5(20
4321
4
3
2
1
pppp
Ip
p
p
p
H k 1 D F b 8 2010
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Homework 1: Due Feb 8, 2010
1. Problem 1.72. Problem 1.9
3. Problem 1.15
4. Problem 1.18
5. Problem 1.20
6. Problem 1.26
7. Problem 1.35