Electronic principles - Chapter 1 doc
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MALVINO
Electronic
PRINCIPLES
SIXTH EDITION
Chapter 1
Introduction
Three kinds of formulas
The definition:
The law:
The derivation:
Invented for a new concept
Summarizes a relationship that exists in nature
Obtained by manipulating other
formulas using mathematics
C =
Q
V
{defines what capacitance is}
Q = CV
f = K
Q
1
Q
2
d
2
{does not require verification}
{verified by experiment}
R
L10 V
An ideal voltage source maintains a constant
output voltage, regardless of the value of R
L
.
The ideal model can be called
the first approximation.
V
R
L
= 10 Volts
R
L10 V
A real voltage source has
a series resistance.
This model is called the
the second approximation.
R
S
V
R
L
< 10 Volts
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.
R
L
1 A
An ideal current source maintains a constant
output current, regardless of the value of R
L
.
The ideal model can be called
the first approximation.
I
R
L
= 1 Ampere
R
L
1 A
I
R
L
< 1 Ampere
A real current source has
a shunt resistance.
R
S
This model is called the
the second approximation.
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
called V
TH
and an equivalent resistance called R
TH
.
6 kΩ
4 kΩ
3 kΩ
R
L
72 V
Remove the load.
Calculate or measure V
TH
across the open terminals.
V
TH
Remove the source.Calculate or measure R
TH
.
R
TH
The input impedance of
a voltmeter should be at least 100 times
greater than the Thevenin resistance to
avoid loading error.
When working with actual circuits,
please remember this guideline:
DMMs are usually not a problem since they
typically have an impedance of 10 MΩ.
6 kΩ
4 kΩ
3 kΩ
R
L
72 V
6 kΩ (R
TH
)
R
L
24 V (V
TH
)
The original
circuit
The Thevenin
equivalent circuit
Norton’s theorem can be used to replace any
linear circuit with an equivalent current source
called I
N
and an equivalent resistance called R
N
.
6 kΩ
4 kΩ
3 kΩ
R
L
72 V
Short the load to find I
N
.
I
N
R
N
is the same as R
TH
.
R
N
6 kΩ
4 kΩ
3 kΩ
R
L
72 V
The original
circuit
The Norton
equivalent circuit
6 kΩ (R
N
)
R
L
4 mA (I
N
)
The Norton
dual
6 kΩ (R
N
)
R
L
4 mA (I
N
)
6 kΩ (R
TH
)
R
L
24 V (V
TH
)
A Thevenin
equivalent circuit
R
N
= R
TH
I
N
=
V
TH
R
TH
Troubleshooting
•
A solder bridge between two lines
effectively shorts them together.
•
A cold solder joint is effectively an open
circuit.
•
An intermittent trouble is one that
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.
•
V = zero x infinity {indeterminate}
A shorted device
•
The voltage across it is zero.
•
The current through it is unknown.
•
I = 0/0 {indeterminate}
10 Ω
100 kΩ
10 Ω
12 V
100 kΩ
A troubleshooting example:
Do the two 10 Ω resistors form
a stiff voltage divider?
Why?
10 Ω
100 kΩ
10 Ω
12 V
100 kΩ
A troubleshooting example:
What are the expected
voltages in this circuit?
10 Ω
100 kΩ
10 Ω
12 V
100 kΩ
A troubleshooting example:
What are some causes for
this voltage being too high?
V
10 Ω
100 kΩ
10 Ω
12 V
100 kΩ
A troubleshooting example:
What are some causes for
this voltage being too low?
V
