Basic Concepts Dasar Rangkaian Elektronika (DRE)

7/29/2019 Basic Concepts Dasar Rangkaian Elektronika (DRE)

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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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Introduction

An electric circuit is an interconnection ofcircuit elements


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Complicated Circuits

Electric circuit of a radio receiver.


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System of Units


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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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Alessandro Antonio Volta

(1745-1827)


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1 A = 10 12A

1A = 10 6A

1nA = 10 9

A


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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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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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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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Electric current due to flow of electronic charge in a conductor.


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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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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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Two Common types of current:(a) Direct current (dc).

(b) Alternating current (ac).


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Conventional current flow:

(a) Positive current flow,(b) Negative current flow.


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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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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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Example 1.3

C5.52

11)28(

2

)3(

2

1

23

2

1

22

1

tt

dtttidtQt


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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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Polarity of voltage vab

.

baab vv


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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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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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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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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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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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Reference polarities for power using the positive sign convention:

(a) absorbing power, (b) supplying power.


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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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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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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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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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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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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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1884 Exhibition


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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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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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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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Symbols for independent voltage sources:

(a) used for constant or time-varying voltage,(b) used for constant voltage (dc).


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Symbol for independent current source.


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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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Symbol for:

(a) dependent voltage source, (b) dependent current source.


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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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The source on the right-hand side is a current-controlled

Voltage source.

E l 1 7


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Example 1.7

E l 1 7


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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

Basic Concepts Dasar Rangkaian Elektronika (DRE)

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