Tài liệu Malvino-EP-01-Introduction pdf

MALVINO
Electronic
Electronic
PRINCIPLES
SIXTH EDITION
Introduction
Introduction
Chapter 1
Three kinds of formulas
The definition:
Invented for a new concept
Q
C =
Q
V
{defines what capacitance is}
{does not require verification}
The law:
Summarizes a relationship that exists in nature
fK
Q
1
Q
2
{ifidb i t}
The
derivation
:
Obtained by manipulating other
f
=

K
d
2
{
ver
ifi
e
d

b
y exper
i
men
t}
The

derivation
:
Obtained

by

manipulating

other

formulas using mathematics
Q=CV
Q

=

CV
An
ideal voltage source
maintains a constant
An

ideal

voltage

source
maintains

a

constant
output voltage, regardless of the value of R
L
.
R
V
10 V lt
R
L
10 V
V
R
L

=
10

V
o
lt
s
The ideal model can be called
the first approximation.
A real voltage source has
a series resistance
a

series

resistance
.
R
L
10 V
R
S
V
R
L
< 10 Volts
L
10

V

R
L
This model is called the
th d i ti
th
e secon
d
approx
i
ma
ti
on.
When R
L
is equal to or greater than 100 times R
S
,areal
When

R
L
is

equal

to

or

greater

than

100

times

R
S
,

a

real
voltage source is stiff and the first approximation can be used.
An
ideal current source
maintains a constant
An

ideal

current

source
maintains

a

constant

output current, regardless of the value of R
L
.
R
I
1A
R
L
1 A
I
R
L
=
1

A
mpere
The ideal model can be called
the first approximation.
A real current source has
a shunt resistance
a

shunt

resistance
.
R
I
1A

R
R
L
1 A
I
R
L
<
1

A
mpere
R
S
This model is called the
th d i ti
th
e secon
d
approx
i
ma
ti
on.
When R
S
is equal to or greater than 100 times R
L
,areal
When

R
S
is

equal

to

or

greater

than

100

times

R
L
,

a

real
current source is stiff and the first approximation can be used.
Thevenin’s theorem can be used to replace any
linear circuit with an equivalent voltage source
linear

circuit

with

an

equivalent

voltage

source
called V
TH
and an equivalent resistance called R
TH
.
6
k
Ω
4
k
Ω
3
k
Ω
R
L
72 V
V

TH
R
TH
TH
TH
Remove the load.
Calculate or measure V
across the open terminals
Remove the source.
Calculate or measure R
TH
.
Calculate

or

measure

V
TH
across

the

open

terminals
.
Remove

the

source.
Calculate

or

measure

R
TH
.
When working with actual circuits,
please remember this
g
uideline:
The input impedance of
a voltmeter should be at least 100 times
greater than the Thevenin resistance to
avoid loading error.
DMMs are usually not a problem since they
DMMs

are

usually

not

a

problem

since

they
typically have an impedance of 10 MΩ.
6k
Ω
6

k
Ω
4
k
Ω
3 kΩ
R
L
72 V
The original
circuit
circuit
6 kΩ (R
TH
)
R
The Thevenin
R
L

24 V (V
TH
)
equivalent circuit
Norton’s theorem can be used to replace any
linear circuit with an equivalent current source
linear

circuit

with

an

equivalent

current

source
called I
N
and an equivalent resistance called R
N
.
6
k
Ω
4
k
Ω

3
k
Ω
R
L
72 V
I
N
R
N
N
N
Short the load to find I
R
N
i
s
th
e

s
am
e
a
s
R
TH
.
Short

the

load

to

find

I
N
.
N
ses es
TH
.
6k
Ω
6

k
Ω
4
k
Ω
3 kΩ
R
L
72 V
The original
circuit

circuit
The Norton
R
4A(I
)
equivalent circuit
6
k
Ω
(R
N
)
R
L
4
m
A

(I
N
)
6 kΩ (R
TH
)
ATh i
R
L
24 V (V
TH
)

A

Th
even
i
n
equivalent circuit
R
N
= R
TH
I
N
=
V
TH
R
TH
The Norton
dual
6 kΩ (R
N
)
R
L
4 mA (I
N
)
Troubleshooting
• A solder bridge between two lines

effectivel
y
shorts them to
g
ether.
yg
• A cold solder joint is effectively an open
circuit
circuit
.
• An intermittent trouble is one that
appears and disappears (could be a cold
appears

and

disappears

(could

be

a

cold

solder joint or a loose connection).
An open device
• The current through it is zero.
•

The voltage across it is unknown
The

voltage

across

it

is

unknown
.
• V = zero x infinity {indeterminate}
A shorted device
• The voltage across it is zero.
•
The current through it is unknown
The

current

through

it

is

unknown
.

• I = 0/0 {indeterminate}
A troubleshooting example:
Do the two 10 Ω resistors form
a sti
ff
volta
g
e divider?
10 Ω
100 kΩ
10
Ω
12 V
100 k
Ω
10

Ω
12

V
100

k
Ω
Wh
y
?
y
A troubleshooting example:

What are the expected
volta
g
es in this circuit?
10 Ω
100
k
Ω
10 Ω
12 V 100 kΩ
A troubleshooting example:
What are some causes for
this volta
g
e bein
g
too hi
g
h?
10 Ω
100 kΩ
10
Ω
12 V
100 k
Ω
V
10

Ω

12

V
100

k
Ω
V
A troubleshooting example:
What are some causes for
this volta
g
e bein
g
too low?
10 Ω
100 kΩ
10
Ω
12 V
100 k
Ω
V
10

Ω
12

V
100

k
Ω
V