Transcript Ohm`s law - Future Academy

Electronics
© by DR. M. Amer
Course Contents
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Introduction
Fundamentals of Semiconductor Devices
P-N Junction Diodes
Bipolar Junction and FET Structures
Semiconductor Devices(circuit element,
filter, power supply, rectification
amplifier)
Introduction to digital circuits.
4/1/2016
Introduction
electronics fundamentals
4/1/2016
Scientific and Engineering Notation
Very large and very small numbers are
represented with scientific and engineering
notation.
47,000,000 = 4.7 x 107 (Scientific Notation)
= 47 x 106 (Engineering Notation)
Scientific and Engineering Notation
0.000 027 = 2.7 x 10-5 (Scientific Notation)
= 27 x 10-6 (Engineering Notation)
0.605 = 6.05 x 10-1 (Scientific Notation)
= 605 x 10-3 (Engineering Notation)
SI Fundamental Units
Quantity
Unit
Length
Mass
Time
Electric current
Temperature
Meter
Kilogram
Second
Ampere
Kelvin
Symbol
m
kg
s
A
K
Some Important Electrical Units
Except for current, all electrical and magnetic
units are derived from the fundamental units.
Current is a fundamental unit.
Quantity
Current
Charge
Voltage
Resistance
Power
Unit
Ampere
Coulomb
Volt
Ohm
Watt
Symbol
A
C
V
W
W
These derived units are
based on fundamental
units from the meterkilogram-second system,
hence are called mks
units.
Engineering Metric Prefixes
Can you
name the
prefixes and
their
meaning?
P
peta
1015
T
tera
1012
G
giga
109
M
mega
106
k
kilo
103
Engineering Metric Prefixes
Can you
name the
prefixes and
their
meaning?
m
milli
10-3
m
micro
10-6
n
nano
10-9
p
pico
10-12
f
femto
10-15
Metric Conversions
When converting from a larger unit to a smaller unit,
move the decimal point to the right. Remember, a
smaller unit means the number must be larger.
Smaller unit
0.47 MW = 470 kW
Larger number
Metric Conversions
When converting from a smaller unit to a larger unit,
move the decimal point to the left. Remember, a larger
unit means the number must be smaller.
Larger unit
10,000 pF = 0.01 mF
Smaller number
Metric Arithmetic
When adding or subtracting numbers with a metric
prefix, convert them to the same prefix first.
10,000 W + 22 kW =
10,000 W + 22,000 W = 32,000 W
Alternatively,
10 kW + 22 kW = 32 kW
Metric Arithmetic
When adding or subtracting numbers with a metric
prefix, convert them to the same prefix first.
200 mA + 1.0 mA =
200 mA + 1,000 mA = 1,200 mA
Alternatively,
0.200 mA + 1.0 mA = 1.2 mA
Review of V, I, and R
Voltage is
the amount of energy per charge available to
move electrons from one point to another in
a circuit and is measured in volts.
the rate of charge flow and is measured in
Current is
amperes.
Resistance is
in ohms.
the opposition to current and is measured
Ohm’s law
The most important fundamental law in electronics is
Ohm’s law, which relates voltage, current, and resistance.
Georg Simon Ohm (1787-1854) formulated the equation
that bears his name:
V
I
R
What is the current in a circuit with a 12 V source if
the resistance is 10 W? 1.2 A
Ohm’s law
If you need to solve for voltage, Ohm’s law is:
V  IR
What is the voltage across a 680 W resistor if the
current is 26.5 mA? 18 V
Ohm’s law
V
If you need to solve for resistance, Ohm’s law is: R 
I
What is the (hot)
resistance of the bulb? 132 W
OFF
V
Hz
115 V
V
mV
A
Range
Autorange
Touch/Hold
1s
1s
10 A
V
40 mA
COM
Fused
Application of Ohm’s law
The resistor is green-blue
brown-gold. What should the
ammeter read?
Power Supply
V
A
+15 V
Gnd
5 V 2A
- +
- +
26.8 mA
+
m
DC Am
eter
-
Energy and Power
In electrical work, the rate energy is dissipated
can be determined from any of three forms of
the power formula.
P  I 2R
P  VI
V2
P
R
Together, the three forms are called Watt’s law.
Energy and Power
What power is dissipated in a 27 W resistor if the
current is 0.135 A?
Given that you know the resistance and current,
substitute the values into P =I 2R.
P  I 2R
 (0.135 A) 2  27 W 
 0.49 W
Energy and Power
What power is dissipated by a heater that draws 12 A
of current from a 120 V supply?
The most direct solution is to substitute into P = IV.
P  IV
 12 A 120 V 
 1440 W
Energy and Power
What power is dissipated in a 100 W resistor with 5 V
across it?
V2
The most direct solution is to substitute into P 
.
R
It is useful to keep in mind that
small resistors operating in low
voltage systems need to be sized
for the anticipated power.
Ampere-hour Rating of Batteries
Expected battery life of batteries is given as the amperehours specification. Various factors affect this, so it is an
approximation. (Factors include rate of current withdrawal,
age of battery, temperature, etc.)
How many hours can you expect to have a
battery deliver 0.5 A if it is rated at 10 Ah?
20 h
Battery
Passive Components
Resistors
Capacitors
Inductors
Diodes
Interface components
25
Electronics 2
Resistors
Values specified in ohms (Ω),
kilo-ohms (K), or mega-ohms
(M)
Marked with value using a code
0 1 2 3 4 5 6 7 8 9 5% 10%
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Electronics 2
Resistor Color Code
Or how to read those little
resistors!
Resistor Color Code
1st band color gives 1st number
2nd band color gives 2nd number
3rd band color gives # of zeros
4th band color gives tolerance or ±
How to read it
- Resistors are color coded for easy
reading.
- To determine the value of a given resistor
look for the gold or silver tolerance band
and hold the resistor with this band to
the right.
Then read the colored bands left to right.
How to read it
- Look at the 1st color band and determine its
color. This maybe difficult on small or oddly
colored resistors. Now look at the chart and
match the "1st & 2nd color band" color to
the "Digit it represents". Write this
number down.
How to read it
- Now look at the 2nd color band and match that
color to the same chart. Write this number
next to the 1st Digit.
- Match the 3rd color band with the chart under
multiplier. This is the number you will multiple
the other 2 numbers by. Write it next to the
other 2 numbers with a multiplication sign
before it.
How to read it
Example:
First color is red which is 2
Second color is black which is 0
Third color is yellow which is 10,000
Tolerance is silver which is 10%
Therefore the equation is:
2 0 x 10,000 = 200,000 Ohms ± 10%
Resistor Color Code Chart
1st. & 2nd Color Band Digit it Represents -----Multiplier----BLACK
0
X1
BROWN
1
X10
RED
2
X100
ORANGE
3
X1,000 or 1K
YELLOW
4
X10,000 or 10K
GREEN
5
X100,000 or 100K
BLUE
6
X1,000,000 or 1M
VIOLET
7
Silver is divide by 100
GRAY
8
Gold is divide by 10
WHITE
 9




Tolerances
Gold= 5%
Silver=10%
None=20%
K or M?
- Many resistors have large amounts of
resistance, so we use prefixes to have a
handy short name
- “k” is for kilo and means 1000 times
- “M” is for mega and means 1,000,000
times (million)
Practice
If you have an
Orange Orange Brown Gold resistor
What is it’s resistance?
The first orange means 3
The second orange means 3
The brown means 1 zero
The gold means ± 5%
So answer is 330 ohms ± 5%
Capacitors
Values specified in microfarads (μF) or
picofarads (pF)
Marked with actual value or a numeric
code
Some varieties are +/- polarized
36
Capacitor types
Ceramic disk
Monolithic ceramic
Dipped siver-mica
Mylar
Mylar
Ceramic disk
Monolithic ceramic
Dipped silvered-mica
Mylar or polyester
Aluminum electrolytic (+/-)
Tantalum (+/-)
Solid tantalum, polarized
37
Radial aluminum electrolytic
Axial aluminum electrolytic
Inductors
Values specified in henries (H), millihenries (mH) and
microhenries (μH)
A coil of wire that may be wound on a core of air or
other non-magnetic material, or on a magnetic core
such as iron powder or ferrite.
Two coils magnetically coupled form a transformer.
38
Inductor types
Molded inductor & air-wound inductor
Ferrite core toroidal transformer
39
Adjustable air-wound inductor
Air wound inductor
Iron powder toroidal inductor
Interface components
Switches
Plugs
Sockets
Panel controls
40
LSU 06/04/2007
Two common plug styles
Sleeve
Ring
Tip
1/8” stereo phone plug
1/8” mono phone plug
Shield
RCA plug
Sleeve
LSU 06/04/2007
Tip
Electronics 2
41
Tip
What Is a Semiconductor?
•Many materials, such as most metals, allow electrical current to
flow through them
•These are known as conductors
•Materials that do not allow electrical current to flow through
them are called insulators
•Pure silicon, the base material of most transistors, is considered
a semiconductor because its conductivity can be modulated by
the introduction of impurities
Semiconductors
A material whose properties are such that
it is not quite a conductor, not quite an
insulator
Some common semiconductors
elemental
Si - Silicon (most common)
Ge - Germanium
Insulators, Semiconductors, and Metals




This separation of the conduction bands determines the electrical
properties of the material
Insulators have a large energy gap
– electrons can’t jump to conduction bands
– no current flows
Conductors (metals) have a very small (or nonexistent) energy gap
– electrons easily jump to conduction bands due to thermal
excitation
– current flows easily
Semiconductors have a moderate energy gap
– only a few electrons can jump to the conduction band
» leaving “holes”
– only a little current can flow