Professional in:
Electronics
BY :Omar aleskandatany
1
contents
1-voltage………………………..3
2-alternating current……………..4
3-direct current…………………..6
4-capacitors……………………..8
5-resistors………………………14
6-diode…………………………23
7-rectifier……………………….25
8-transformer…………………...28
9-power (watt).................................31
10-resistance(ohm)..........................33
11-light emitting diodes………..34
12-power supply………………..36
13-inductor..................................39
2
1-voltage
Voltage, electrical potential difference, electric tension or electric pressure
(denoted ∆V) and measured in units of electric potential: volts, or joules per
coulomb is the electric potential difference between two points, or the
difference in electric potential energy of a unit charge transported between
two points.[1] Voltage is equal to the work done per unit charge against a
static electric field to move the charge between two points. A voltage may
represent either a source of energy (electromotive force), or lost, used, or
stored energy (potential drop). A voltmeter can be used to measure the
voltage (or potential difference) between two points in a system; usually a
common reference potential such as the ground of the system is used as
one of the points. Voltage can be caused by static electric fields, by electric
current through a magnetic field, by time-varying magnetic fields, or some
combination of these three.
Voltage is electric potential energy per unit charge, measured in joules per
coulomb ( = volts). It is often referred to as "electric potential", which then
must be distinguished from electric potential energy by noting that the
"potential" is a "per-unit-charge" quantity. Like mechanical potential energy,
the zero of potential can be chosen at any point, so the difference in
voltage is the quantity which is physically meaningful.
2-
3
alternating current (AC)
---------------------------------------------------It is the input of our wall and all electronic devices need alternating current
to work.
AC voltage may be increased or decreased with a transformer. Use of a
higher voltage leads to significantly more efficient transmission of power.
The power losses in a conductor are a product of the square of the current
and the resistance of the conductor, described by the formula
This means that when transmitting a fixed power on a given wire, if the
current is doubled, the power loss will be four times greater.
Mathematics of AC voltages
Alternating currents are accompanied (or caused) by alternating voltages.
An AC voltage v can be described mathematically as a function of time by
the following equation:
History of alternating current
The first alternator to produce alternating current was a dynamo
electric generator based on Michael Faraday's principles constructed
by the French instrument maker Hippolyte Pixii in 1832.] Pixii later
added a commutator to his device to produce the (then) more
commonly used direct current. The earliest recorded practical
application of alternating current is by Guillaume Duchenne, inventor
and developer of electrotherapy. In 1855, he announced that AC was
4
superior to direct current for electrotherapeutic triggering of muscle
contractions.
Alternating current technology had first developed in Europe due to the
work of Guillaume Duchenne (1850s), The Hungarian Ganz Works (1870s),
Sebastian Ziani de Ferranti (1880s), Lucien Gaulard, and Galileo Ferraris.
In 1876, Russian engineer Pavel Yablochkov invented a lighting system
based on a set of induction coils where the primary windings were
connected to a source of AC. The secondary windings could be connected
to several 'electric candles' (arc lamps) of his own design.[5][6] The coils
Yablochkov employed functioned essentially as transformers.[5]
In 1878, the Ganz factory, Budapest, Hungary, began manufacturing
equipment for electric lighting and, by 1883, had installed over fifty systems
in Austria-Hungary. Their AC systems used arc and incandescent lamps,
generators, and other equipment.[7]
A power transformer developed by Lucien Gaulard and John Dixon Gibbs
was demonstrated in London in 1881, and attracted the interest of
Westinghouse. They also exhibited the invention in Turin in 1884.
3-direct current
The first alternator to produce alternating current was a dynamo electric
generator based on Michael Faraday's principles constructed by the French
instrument maker Hippolyte Pixii in 1832. Pixii later added a commutator to
his device to produce the (then) more commonly used direct current. The
5
earliest recorded practical application of alternating current is by Guillaume
Duchenne, inventor and developer of electrotherapy. In 1855, he
announced that AC was superior to direct current for electrotherapeutic
triggering of muscle contractions.
Alternating current technology had first developed in Europe due to the
work of Guillaume Duchenne (1850s), The Hungarian Ganz Works (1870s),
Sebastian Ziani de Ferranti (1880s), Lucien Gaulard, and Galileo Ferraris.
In 1876, Russian engineer Pavel Yablochkov invented a lighting system
based on a set of induction coils where the primary windings were
connected to a source of AC. The secondary windings could be connected
to several 'electric candles' (arc lamps) of his own design. The coils
Yablochkov employed functioned essentially as transformers.
In 1878, the Ganz factory, Budapest, Hungary, began manufacturing
equipment for electric lighting and, by 1883, had installed over fifty systems
in Austria-Hungary. Their AC systems used arc and incandescent lamps,
generators, and other equipment.
A power transformer developed by Lucien Gaulard and John Dixon Gibbs
was demonstrated in London in 1881, and attracted the interest of
Westinghouse. They also exhibited the invention in Turin in 1884.
Definition
The term DC is used to refer to power systems that use only one polarity of
voltage or current, and to refer to the constant, zero-frequency, or slowly
varying local mean value of a voltage or current.
-----------------------------------Direct-current installations usually have different types of sockets,
connectors, switches, and fixtures, mostly due to the low voltages used,
6
from those suitable for alternating current. It is usually important with a
direct-current appliance not to reverse polarity unless the device has a
diode bridge to correct for this (most battery-powered devices do not).
4-capacitors
------------------------------------------------------------------
-----------
the capacitor it is a part in electronics that is used in every electronic device
.
The capacitor :is a part that works like a mini battery
but it empties voltage in a very fast way.
7
it consists of :
2 metallic plates between them a dielectric material as shown in
fig.1
now lets see some dielectrics breakdown voltage:
240v
window glass
480-551v
polyethylene
1651v
distilled water
1016v
high vacuum
1016v
silicon
3v
air
so we deduce that :
1-distilled water has the highest breakdown voltage
2-high vacuum and silicon are equal
3-window glass and polyethylene have a medium
-breakdown voltage
4-air has a low breakdown voltage
--------------------------------------------------------------------------------------------LETS MAKE ONE :
Needed:
8
1-paper
2-aluminum foil
3-pritt stick
Steps:
1-cut 2 pieces of foil
2-stick them on both sides of the paper bir
capacitor types
Practical capacitors are available commercially in many different forms.
The type of internal dielectric, the structure of the plates and the device
packaging all strongly affect the characteristics of the capacitor, and its
applications.
Values available range from very low (picofarad range; while arbitrarily low
values are in principle possible, stray (parasitic) capacitance in any circuit
is the limiting factor) to about 5 kF supercapacitors.
Above approximately 1 microfarad electrolytic capacitors are usually used
because of their small size and low cost compared with other technologies,
unless their relatively poor stability, life and polarised nature make them
unsuitable. Very high capacity supercapacitors use a porous carbon-based
electrode material.
dielectric materials
Most types of capacitor include a dielectric spacer, which increases their
capacitance. These dielectrics are most often insulators. However, low
capacitance devices are available with a vacuum between their plates,
which allows extremely high voltage operation and low losses. Variable
capacitors with their plates open to the atmosphere were commonly used in
radio tuning circuits. Later designs use polymer foil dielectric between the
moving and stationary plates, with no significant air space between them.
9
In order to maximise the charge that a capacitor can hold, the dielectric
material needs to have as high a permittivity as possible, while also having
as high a breakdown voltage as possible.
Several solid dielectrics are available, including paper, plastic, glass, mica
and ceramic materials. Paper was used extensively in older devices and
offers relatively high voltage performance. However, it is susceptible to
water absorption, and has been largely replaced by plastic film capacitors.
Plastics offer better stability and aging performance, which makes them
useful in timer circuits, although they may be limited to low operating
temperatures and frequencies. Ceramic capacitors are generally small,
cheap and useful for high frequency applications, although their
capacitance varies strongly with voltage and they age poorly. They are
broadly categorized as class 1 dielectrics, which have predictable variation
of capacitance with temperature or class 2 dielectrics, which can operate at
higher voltage.
The arrangement of plates and dielectric has many variations depending on
the desired ratings of the capacitor. For small values of capacitance
(microfarads and less), ceramic disks use metallic coatings, with wire leads
bonded to the coating. Larger values can be made by multiple stacks of
plates and disks. Larger value capacitors usually use a metal foil or metal
film layer deposited on the surface of a dielectric film to make the plates,
and a dielectric film of impregnated paper or plastic – these are rolled up to
save space. To reduce the series resistance and inductance for long
plates, the plates and dielectric are staggered so that connection is made
at the common edge of the rolled-up plates, not at the ends of the foil or
metalized film strips that comprise the plates.
10
Capacitor markings
Most capacitors have numbers printed on their bodies to indicate their
electrical characteristics. Larger capacitors like electrolytics usually display
the actual capacitance together with the unit (for example, 220 μF). Smaller
capacitors like ceramics, however, use a shorthand consisting of three
numbers and a letter, where the numbers show the capacitance in pF
(calculated as XY × 10Z for the numbers XYZ) and the letter indicates the
tolerance (J, K or M for ±5%, ±10% and ±20% respectively).
Additionally, the capacitor may show its working voltage, temperature and
other relevant characteristics.
Example
A capacitor with the text 473K 330V on its body has a capacitance of 47 ×
103 pF = 47 nF (±10%) with a working voltage of 330 V. The working
voltage of a capacitor is the highest voltage that can be applied across it
without undue risk of breaking down the dielectric layer.
Energy storage
A capacitor can store electric energy when disconnected from its charging
circuit, so it can be used like a temporary battery, or like other types of
rechargeable energy storage system.[29] Capacitors are commonly used in
electronic devices to maintain power supply while batteries are being
changed. (This prevents loss of information in volatile memory.)
capacitor behaviour in
1-DC circuits
11
A series circuit containing only a resistor, a capacitor, a switch and a
constant DC source of voltage V0 is known as a charging circuit.If the
capacitor is initially uncharged while the switch is open, and the switch is
closed at t0, it follows from Kirchhoff's voltage law that
Kirchhoff’s voltage law :
The directed sum of the electrical potential differences (voltage) around any
closed network is zero, or:
More simply, the sum of the emfs in any closed loop is equivalent to the
sum of the potential drops in that loop, or:
The algebraic sum of the products of the resistances of the conductors and
the currents in them in a closed loop is equal to the total emf available in
that loop.
2-AC circuits
Impedance, the vector sum of reactance and resistance, describes the
phase difference and the ratio of amplitudes between sinusoidally varying
voltage and sinusoidally varying current at a given frequency. Fourier
analysis allows any signal to be constructed from a spectrum of
frequencies, whence the circuit's reaction to the various frequencies may
be found. The reactance and impedance of a capacitor are respectively
-------------------------------------------------------------------------------------------------------
12
5-Resistors
A resistor is a passive two-terminal electrical
component that implements electrical
resistance as a circuit element. Resistors act to reduce current flow, and, at the same
time, act to lower voltage levels within circuits. Resistors may have fixed resistances or
variable resistances, such as those found in thermistors, varistors, trimmers,
photoresistors and potentiometers.
ohm’s law
he behavior of an ideal resistor is dictated by the relationship specified by Ohm's law:
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I),
where the constant of proportionality is the resistance (R).
Equivalently, Ohm's law can be stated:
Lead arrangements
through-hole components typically have leads leaving the body axially. Others have
leads coming off their body radially instead of parallel to the resistor axis. Other
13
components may be SMT (surface mount technology) while high power resistors may
have one of their leads designed into the heat sink.
Carbon composition
Carbon composition resistors consist of a solid cylindrical resistive element with
embedded wire leads or metal end caps to which the lead wires are attached. The body
of the resistor is protected with paint or plastic. Early 20th-century carbon composition
resistors had uninsulated bodies; the lead wires were wrapped around the ends of the
resistance element rod and soldered. The completed resistor was painted for colorcoding of its value.
The resistive element is made from a mixture of finely ground (powdered) carbon and
an insulating material (usually ceramic). A resin holds the mixture together. The
resistance is determined by the ratio of the fill material (the powdered ceramic) to the
carbon. Higher concentrations of carbon— a good conductor— result in lower
resistance. Carbon composition resistors were commonly used in the 1960s and earlier,
but are not so popular for general use now as other types have better specifications,
such as tolerance, voltage dependence, and stress (carbon composition resistors will
change value when stressed with over-voltages). Moreover, if internal moisture content
(from exposure for some length of time to a humid environment) is significant, soldering
heat will create a non-reversible change in resistance value. Carbon composition
resistors have poor stability with time and were consequently factory sorted to, at best,
only 5% tolerance.[5] These resistors, however, if never subjected to overvoltage nor
overheating were remarkably reliable considering the component's size. [6]
Carbon composition resistors are still available, but comparatively quite costly. Values
ranged from fractions of an ohm to 22 megohms. Due to their high price, these resistors
are no longer used in most applications. However, they are used in power supplies and
welding controls.
14
Printed carbon resistor
Carbon composition resistors can be printed directly onto printed circuit
board (PCB) substrates as part of the PCB manufacturing process. Whilst
this technique is more common on hybrid PCB modules, it can also be
used on standard fibreglass PCBs. Tolerances are typically quite large, and
can be in the order of 30%. A typical application would be non-critical pullup resistors
Color code
The axial lead carbon resistors measured by the color codes marked on
them. Information such as resistance value, tolerance, temperature
coefficient measured by the color codes, and the amount of power
(wattage) identified by the size.
The color bands of the carbon resistors can be four, five or, six bands, for
all the first two bands represent first two digits to measure their value in
ohms. The third band of a four-banded resistor represents multiplier and
the fourth band as tolerance. Whereas, the five and six color-banded
resistors, the third band rather represents as third digit but the fourth and
fifth bands represent as multiplier and tolerance respectively. Only the sixth
band represents temperature coefficient in a six-banded resistor.
The measuring digits against color codes given in the following table:
15
Temperature Coefficient
Tolerance Multiplier 1st. Two Digits
Color
-
-
100
0
Black
100
± 1%
101
1
Brown
50
± 2%
102
2
Red
15
-
103
3
Orange
25
-
104
4
Yellow
0.5
-
105
5
Green
0.25
-
106
6
Blue
0.1
-
107
7
Violet
-
-
108
8
Grey
-
-
109
9
White
-
± 10%
10-2
-
Silver
-
± 5%
10-1
-
Gold
16
Surface
mounted resistors are printed with numerical values in a code
related to that used on axial resistors. Standard-tolerance surface-mount
technology (SMT) resistors are marked with a three-digit code, in which the
first two digits are the first two significant digits of the value and the third
digit is the power of ten (the number of zeroes). For example:
= 33 × 104 ohms = 330
33
kohms
4
= 22 × 102 ohms = 2.2
22
k ohms
2
= 47 × 103 ohms = 47
47
kilohms
3
= 10 × 105 ohms = 1
10
megohm
5
Resistances less than 100 ohms are written: 100, 220, 470. The final zero
represents ten to the power zero, which is 1. For example:
= 10 × 100 ohm = 10 10
ohms
0
= 22 × 100 ohm = 22 22
ohms
0
Sometimes these values are marked as 10 or 22 to prevent a mistake.
17
Resistances less than 10 ohms have 'R' to indicate the position of the
decimal point (radix point). For example:
= 4.7
4R7
ohms
= 0.30
R30
ohms
0
= 0.22
0R2
ohms
2
= 0.01
0R0
ohms
1
Precision resistors are marked with a four-digit code, in which the first three
digits are the significant figures and the fourth is the power of ten. For
example:
= 100 × 101 ohms =
100
1.00 kilohm
1
= 499 × 102 ohms =
499
49.9 kilohm
2
= 100 × 100 ohm = 100
100
ohms
0
18
000 and 0000 sometimes appear as values on surface-mSurface mounted
resistors are printed with numerical values in a code related to that used on
axial resistors. Standard-tolerance surface-mount technology (SMT)
resistors are marked with a three-digit code, in which the first two digits are
the first two significant digits of the value and the third digit is the power of
ten (the number of zeroes). For example:
= 33 × 104 ohms = 330
33
kilohms
4
= 22 × 102 ohms = 2.2
2
kilohms
2
= 47 × 103 ohms = 47
47
kilohms
3
= 10 × 105 ohms = 1
10
megohm
5
Resistances less than 100 ohms are written: 100, 220, 470. The final zero
represents ten to the power zero, which is 1. For example:
= 10 × 100 ohm = 10 10
ohms
0
= 22 × 100 ohm = 22 22
ohms
0
Sometimes these values are marked as 10 or 22 to prevent a mistake.
19
Resistances less than 10 ohms have 'R' to indicate the position of the
decimal point (radix point). For example:
= 4.7
4R7
ohms
= 0.30
R30
ohms
0
= 0.22
0R2
ohms
2
= 0.01
0R0
ohms
1
Precision resistors are marked with a four-digit code, in which the first three
digits are the significant figures and the fourth is the power of ten. For
example:
= 100 × 101 ohms =
100
1.00 kilohm
1
= 499 × 102 ohms =
499
49.9 kilohm
2
= 100 × 100 ohm = 100
100
ohms
0
20
000 and 0000 sometimes appear as values on surface-mount zero-ohm
links, since these have (approximately) zero resistance.
More recent surface-mount resistors are too small, physically, to permit
practical markings to be applied.
links, since these have (approximately) zero resistance.
More recent surface-mount resistors are too small, physically, to permit
practical markings to be applied.
.
6-diode
In electronics, a diode is a two-terminal electronic component with
asymmetric conductance; it has low (ideally zero)resistance to current in
21
one direction, and high (ideally infinite) resistance in the other. A
semiconductor diode, the most common type today, is a crystalline piece of
semiconductor material with a p–n junction connected to two electrical
terminals.[5] A vacuum tube diode has two
electrodes, a plate (anode) and a heated
cathode. Semiconductor diodes were the first
semiconductor electronic devices. The
discovery of crystals' rectifying abilities was
made by German physicist Ferdinand Braun in
1874. The first semiconductor diodes, called
cat's whisker diodes, developed around 1906,
were made of mineral crystals such as galena.
Today, most diodes are made of silicon, but other semiconductors such as
selenium or germanium are sometimes used.
Main functions
The most common function of a diode is to allow an electric current to pass
in one direction (called the diode's forward direction), while blocking
current in the opposite direction (the reverse direction). Thus, the diode
can be viewed as an electronic version of a check valve. This
unidirectional behavior is called rectification, and is used to convert
alternating current to direct current, including extraction of modulation
from radio signals in radio receivers—these diodes are forms of rectifiers.
However, diodes can have more complicated behavior than this simple on–
off action, due to their nonlinear current-voltage characteristics.
Semiconductor diodes begin conducting electricity only if a certain
threshold voltage or cut-in voltage is present in the forward direction (a
state in which the diode is said to be forward-biased). The voltage drop
across a forward-biased diode varies only a little with the current, and is a
function of temperature; this effect can be used as a temperature sensor or
voltage reference.
22
Semiconductor diodes' current–voltage characteristic can be tailored by
varying the semiconductor materials and doping, introducing impurities into
the materials. These are exploited in special-purpose diodes that perform
many different functions. For example, diodes are used to regulate voltage
(Zener diodes), to protect circuits from high voltage surges (avalanche
diodes), to electronically tune radio and TV receivers (varactor diodes), to
generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT
diodes), and to produce light (light emitting diodes). Tunnel diodes exhibit
negative resistance, which makes them useful in some types of circuits.
converting ac to dc
Rectifiers are constructed from diodes, where they are used to convert
alternating current (AC) electricity into direct current (DC). Automotive
alternators are a common example, where the diode, which rectifies the AC
into DC, provides better performance than the commutator or earlier,
dynamo. Similarly, diodes are also used in Cockcroft–Walton voltage
multipliers to convert AC into higher DC voltages.
7rectifier
A rectifier is an electrical device that converts alternating current (AC),
which periodically reverses direction, to direct current (DC), which flows in
23
only one direction. The process is known as rectification. Physically,
rectifiers take a number of forms, including vacuum tube diodes, mercuryarc valves, copper and selenium oxide rectifiers,semiconductor diodes,
silicon-controlled rectifiers and other silicon-based semiconductor switches.
Historically, even synchronous electromechanical switches and motors
have been used. Early radio receivers, called crystal radios, used a "cat's
whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve
as a point-contact rectifier or "crystal detector".
Rectifiers have many uses, but are often found serving as components of
DC power supplies and high-voltage direct current power transmission
systems. Rectification may serve in roles other than to generate direct
current for use as a source of power. As noted, detectors of radio signals
serve as rectifiers. In gas heating systems flame rectification is used to
detect presence of flame.
Because of the alternating nature of the input AC sine wave, the process of
rectification alone produces a DC current that, though unidirectional,
consists of pulses of current. Many applications of rectifiers, such as power
supplies for radio, television and computer equipment, require a steady
constant DC current (as would be produced by a battery). In these
applications the output of the rectifier is smoothed by an electronic filter to
produce a steady current.
A more complex circuitry device that performs the opposite function,
converting DC to AC, is called an inverter.
A rectifier is an electrical device that converts alternating current (AC),
which periodically reverses direction, to direct current (DC), which flows in
only one direction. The process is known as rectification. Physically,
24
rectifiers take a number of forms, including vacuum tube diodes, mercuryarc valves, copper and selenium oxide rectifiers,semiconductor diodes,
silicon-controlled rectifiers and other silicon-based semiconductor switches.
Historically, even synchronous electromechanical switches and motors
have been used. Early radio receivers, called crystal radios, used a "cat's
whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve
as a point-contact rectifier or "crystal detector".
Rectifiers have many uses, but are often found serving as components of
DC power supplies and high-voltage direct current power transmission
systems. Rectification may serve in roles other
than to generate direct current for use as a
source of power. As noted, detectors of radio
signals serve as rectifiers. In gas heating
systems flame rectification is used to detect
presence of flame.
Because of the alternating nature of the input AC sine wave, the process of
rectification alone produces a DC current that, though unidirectional,
consists of pulses of current. Many applications of rectifiers, such as power
supplies for radio, television and computer equipment, require a steady
constant DC current (as would be produced by a battery). In these
applications the output of the rectifier is smoothed by an electronic filter to
produce a steady current.
A more complex circuitry device that performs the opposite function,
converting DC to AC, is called an inverter.
25
8-transformer
A transformer is an electrical device that transfers energy between two
circuits through electromagnetic induction. A transformer may be used as a
safe and efficient voltage converter to change the AC voltage at its input to
a higher or lower voltage at its output. Other uses include current
conversion, isolation with or without changing voltage and impedance
conversion.
A transformer most commonly consists of two windings of wire that are
wound around a common core to provide tight electromagnetic coupling
between the windings. The core material is often a laminated iron core. The
coil that receives the electrical input energy is referred to as the primary
winding, while the output coil is called the secondary winding.
An alternating electric current flowing through the primary winding (coil) of a
transformer generates a varying electromagnetic field in its surroundings
which causes a varying magnetic flux in the core of the transformer. The
varying electromagnetic field in the vicinity of the secondary winding
induces an electromotive force in the secondary winding, which appears a
26
voltage across the output terminals. If a load impedance is connected
across the secondary winding, a current flows
through the secondary winding drawing power
from the primary winding and its power source.
A transformer cannot operate with direct current;
although, when it is connected to a DC source, a
transformer typically produces a short output
pulse as the current rises.
application
A transformer is an electrical device that transfers energy between two
circuits through electromagnetic induction. A transformer may be used as a
safe and efficient voltage converter to change the AC voltage at its input to
a higher or lower voltage at its output. Other uses include current
conversion, isolation with or without changing voltage and impedance
conversion.
A transformer most commonly consists of two windings of wire that are
wound around a common core to provide tight electromagnetic coupling
between the windings. The core material is often a laminated iron core. The
coil that receives the electrical input energy is referred to as the primary
winding, while the output coil is called the secondary winding.
An alternating electric current flowing through the primary winding (coil) of a
transformer generates a varying electromagnetic field in its surroundings
which causes a varying magnetic flux in the core of the transformer. The
varying electromagnetic field in the vicinity of the secondary winding
induces an electromotive force in the secondary winding, which appears a
voltage across the output terminals. If a load impedance is connected
27
across the secondary winding, a current flows through the secondary
winding drawing power from the primary winding and its power source.
A transformer cannot operate with direct current; although, when it is
connected to a DC source, a transformer typically produces a short output
pulse as the current rises.
9-power (watt)
Electric power is the rate at which electric energy is transferred by an
electric circuit. The SI unit of power is the watt, one joule per second.
28
Electric power is usually produced by electric generators, but can also be
supplied by sources such as electric batteries. Electric power is generally
supplied to businesses and homes by the electric power industry. Electric
power is usually sold by the kilowatt hour (3.6 MJ) which is the product of
power in kilowatts multiplied by running time in hours. Electric utilities
measure power using an electricity meter, which keeps a running total of
the electric energy delivered to a customer.
definition
Electric power is the rate at which electric energy is transferred by an
electric circuit. The SI unit of power is the watt, one joule per second.
Electric power is usually produced by electric generators, but can also be
supplied by sources such as electric batteries. Electric power is generally
supplied to businesses and homes by the electric power industry. Electric
power is usually sold by the kilowatt hour (3.6 MJ) which is the product of
power in kilowatts multiplied by running time in hours. Electric utilities
measure power using an electricity meter, which keeps a running total of
the electric energy delivered to a customer.
Electricity generation
The fundamental principles of electricity generation were discovered during
the 1820s and early 1830s by the British scientist Michael Faraday. His
basic method is still used today: electricity is generated by the movement of
a loop of wire, or disc of copper between the poles of a magnet.[1]
29
For electric utilities, it is the first process in the delivery of electricity to
consumers. The other processes, electricity transmission, distribution, and
electrical power storage and recovery using pumped-storage methods are
normally carried out by the electric power industry.
Electricity is most often generated at a power station by electromechanical
generators, primarily driven by heat engines fueled by chemical combustion
or nuclear fission but also by other means such as the kinetic energy of
flowing water and wind. There are many other technologies that can be and
are used to generate electricity such as solar photovoltaics and geothermal
power.
power(W) = current (A) X voltage
(V)
10-resistance (ohm)
The electrical resistance of an electrical conductor is the opposition to the
passage of an electric current through that conductor. The inverse quantity
is electrical conductance, the ease with which an electric current passes.
Electrical resistance shares some conceptual parallels with the mechanical
30
notion of friction. The SI unit of electrical resistance is the ohm(Ω), while
electrical conductance is measured in siemens (S).
An object of uniform cross section has a resistance proportional to its
resistivity and length and inversely proportional to its cross-sectional area.
All materials show some resistance, except for superconductors, which
have a resistance of zero.
The resistance (R) of an object is defined as the ratio of voltage across it
(V) to
current through it (I),
while
the conductance (G)
is the
inverse:
11-light emitting diode(L.E.D.)
A light-emitting 1diode (LED) is a two-lead semiconductor light source
that resembles a basic pn-junction diode, except that an LED also emits
light.[7] When an LED's anode lead has a voltage that is more positive than
its cathode lead by at least the LED's forward voltage drop, current flows.
Electrons are able to recombine with holes within the device, releasing
energy in the form of photons. This effect is called electroluminescence,
31
and the color of the light (corresponding to the energy of the photon) is
determined by the energy band gap of the semiconductor.
An LED is often small in area (less than 1 mm2), and integrated optical
components may be used to shape its radiation pattern.[8]
Appearing as practical electronic components in 1962,[9] the earliest LEDs
emitted low-intensity infrared light. Infrared LEDs are still frequently used
as transmitting elements in remote-control circuits, such as those in remote
controls for a wide variety of consumer electronics. The first visible-light
LEDs were also of low intensity, and limited to red. Modern LEDs are
available across the visible, ultraviolet, and infrared wavelengths, with very
high brightness.
Early LEDs were often used as indicator lamps for electronic devices,
replacing small incandescent bulbs. They were soon packaged into
numeric readouts in the form of seven-segment displays, and were
commonly seen in digital clocks.
Recent developments in LEDs permit them to be used in environmental
and task lighting. LEDs have many advantages over incandescent light
sources including lower energy consumption, longer lifetime, improved
physical robustness, smaller size, and faster switching. Light-emitting
diodes are now used in applications as diverse as aviation
lighting,automotive headlamps, advertising, general lighting, traffic signals,
and camera flashes. However, LEDs powerful enough for room lighting are
still relatively expensive, and require more precise current and heat
management than compact fluorescent lamp sources of comparable
output.
32
LEDs have allowed new text, video displays, and sensors to be developed,
while their high switching rates are also useful in advanced
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12-power supply
A power supply is a device that supplies electric power to an electrical
load. The term is most commonly applied to electric power converters that
convert one form of electrical energy to another, though it may also refer to
devices that convert another form of energy (mechanical, chemical, solar)
to electrical energy. A regulated power supply is one that controls the
33
output voltage or current to a specific value; the controlled value is held
nearly constant despite variations in either load current or the voltage
supplied by the power supply's energy source.
Every power supply must obtain the energy it supplies to its load, as well as
any energy it consumes while performing that .
Types of power supply
Power supplies for electronic devices can be broadly divided into linefrequency (or "conventional") and switching power supplies. The linefrequency supply is usually a relatively simple design, but it becomes
increasingly bulky and heavy for high-current equipment due to the need
for large mains-frequency transformers and heat-sinked electronic
regulation circuitry. Conventional line-frequency power supplies are
sometimes called "linear", but that is a misnomer because the conversion
from AC voltage to DC is inherently non-linear when the rectifiers feed into
capacitive reservoirs. Linear voltage regulators produce regulated output
voltage by means of an active voltage divider that consumes energy, thus
making efficiency low. A switched-mode supply of the same rating as a
line-frequency supply will be smaller, is usually more
efficient, but would be more complex.
1-DC power supply
An AC powered unregulated power supply usually uses a transformer to
convert the voltage from the wall outlet (mains) to a different, nowadays
usually lower, voltage. If it is used to produce DC, a rectifier is used to
convert alternating voltage to a pulsating direct voltage, followed by a filter,
comprising one or more capacitors, resistors, and sometimes inductors, to
34
filter out (smooth) most of the pulsation. A small remaining unwanted
alternating voltage component at mains or twice mains power frequency
(depending upon whether half- or full-wave rectification is used)—ripple—is
unavoidably superimposed on the direct output voltage.
For purposes such as charging batteries the ripple is not a problem, and
the simplest unregulated mains-powered DC power supply circuit consists
of a transformer driving a single diode in series with a resistor.
Before the introduction of solid-state electronics, equipment used valves
(vacuum tubes) which required high voltages; power supplies used step-up
transformers, rectifiers, and filters to generate one or more direct voltages
of some hundreds of volts, and a low alternating voltage for filaments. Only
the most advanced equipment used expensive and bulky regulated power
supplies.
2-AC power supply
An AC power supply typically takes the voltage from a wall outlet (mains
supply) and lowers it to the desired voltage. Some filtering may take place
as well.
3-linear regulated power supply
The voltage produced by an unregulated power supply will vary depending
on the load and on variations in the AC supply voltage. For critical
electronics applications, a linear regulator may be used to set the voltage to
a precise value, stabilized against fluctuations in input voltage and load.
The regulator also greatly reduces the ripple and noise in the output direct
35
current. Linear regulators often provide current limiting, protecting the
power supply and attached circuit from overcurrent.
Adjustable linear power supplies are common laboratory and service shop
test equipment, allowing the output voltage to be adjusted over a range.
For example, a bench power supply used by circuit designers may be
adjustable up to 30 volts and up to 5 amperes output. Some can be driven
by an external signal, for example, for applications requiring a pulsed
output
4-switched-mode power supply
In a switched-mode power supply (SMPS), the AC mains input is directly
rectified and then filtered to obtain a DC voltage. The resulting DC voltage
is then switched on and off at a high frequency by electronic switching
circuitry, thus producing an AC current that will pass through a highfrequency transformer or inductor. Switching occurs at a very high
frequency (typically 10 kHz — 1 MHz), thereby enabling the use of
transformers and filter capacitors that are much smaller, lighter, and less
expensive than those found in linear power supplies operating at mains
frequency. After the inductor or transformer secondary, the high frequency
AC is rectified and filtered to produce the DC output voltage. If the SMPS
uses an adequately insulated high-frequency transformer, the output will be
electrically isolated from the mains; this feature is often essential for safety.
Switched-mode power supplies are usually regulated, and to keep the
output voltage constant, the power supply employs a feedback controller
that monitors current drawn by the load. The switching duty cycle increases
as power output requirements increase.
SMPSs often include safety features such as current limiting or a crowbar
circuit to help protect the device and the user from harm.[1] In the event that
36
an abnormal high-current power draw is detected, the switched-mode
supply can assume this is a direct short and will shut itself down before
damage is done. PC power supplies often provide a power good signal to
the motherboard; the absence of this signal prevents operation when
abnormal supply voltages are present.
SMPSs have an absolute limit on their minimum current output.[2] They are
only able to output above a certain power level and cannot function below
that point. In a no-load condition the frequency of the power slicing circuit
increases to great speed, causing the isolated transformer to act as a Tesla
coil, causing damage due to the resulting very high voltage power spikes.
Switched-mode supplies with protection circuits may briefly turn on but then
shut down when no load has been detected. A very small low-power
dummy load such as a ceramic power resistor or 10-watt light bulb can be
attached to the supply to allow it to run with no primary load attached.
Power factor has become an issue of concern for computer manufacturers.
Switched mode power supplies have traditionally been a source of power
line harmonics and have a very poor power factor. The rectifier input stage
distorts the waveshape of current drawn from the supply; this can produce
adverse effects on other loads. The distorted current causes extra heating
in the wires and distribution equipment. Switched mode power supplies in a
building can result in poor power quality for other utility customers.
Customers may face higher electric bills for a low power factor load.
Some switch-mode power supplies use filters or additional switching stages
in the incoming rectifier circuit to improve the waveform of the current taken
from the AC line. This adds to the circuit complexity. Many computer power
supplies built in the last few years now include power factor correction built
37
right into the switched-mode supply, and may advertise the fact that they
offer 1.0 power factor.
5-AC adaptor
A power supply that is built into an AC mains power plug is known as a
"plug pack" or "plug-in adapter", or by slang terms such as "wall wart". They
are even more diverse than their names; often with either the same kind of
DC plug offering different voltage or polarity, or a different plug offering the
same voltage. "Universal" adapters attempt to replace missing or damaged
ones, using multiple plugs and selectors for different voltages and
polarities. Replacement power supplies must match the voltage of, and
supply at least as much current as, the original power supply.
The least expensive AC units consist only of a small transformer, while DC
adapters include a few additional diodes. Whether or not a load is
connected to the power adapter, the transformer has a magnetic field
continuously present and normally cannot be completely turned off unless
unplugged.
Because they consume standby power, they are sometimes known as
"electricity vampires" and may be plugged into a power strip to allow
turning them off.
In contrast, switched-mode power supplies can cut off leaky electrolytecapacitors, use powerless MOSFETs, and reduce their working frequency
to get a gulp of energy once in a while to power, for example, a clock,
which would otherwise need a battery.
38
13-inductor
An inductor, also called a coil or reactor, is a passive two-terminal
electrical component which resists changes in electric current passing
through it. It consists of a conductor such as a wire, usually wound into a
coil. When a current flows through it, energy is stored temporarily in a
magnetic field in the coil. When the current flowing through an inductor
changes, the time-varying magnetic field induces a voltage in the
conductor, according to Faraday’s law of electromagnetic induction, which
opposes the change in current that created it.
An inductor is characterized by its inductance, the ratio of the voltage to the
rate of change of current, which has units of henries (H). Inductors have
values that typically range from 1 µH (10-6H) to 1 H. Many inductors have a
magnetic core made of iron or ferrite inside the coil, which serves to
increase the magnetic field and thus the inductance. Along with capacitors
and resistors, inductors are one of the three passive linear circuit elements
that make up electric circuits. Inductors are widely used in alternating
current (AC) electronic equipment, particularly in radio equipment. They are
used to block the flow of AC current while allowing DC to pass; inductors
designed for this purpose are called chokes. They are also used in
electronic filters to separate signals of different frequencies, and in
39
combination with capacitors to make tuned circuits, used to tune radio and
TV receivers.
An inductor, also called a coil or reactor, is a passive two-terminal
electrical component which resists changes inelectric current passing
through it. It consists of a conductor such as a wire, usually wound into a
coil. When a current flows through it, energy is stored temporarily in a
magnetic field in the coil. When the current flowing through an inductor
changes, the time-varying magnetic field induces a voltage in the
conductor, according to Faraday’s law of electromagnetic induction, which
opposes the change in current that created it.
An inductor is characterized by its inductance, the ratio of the voltage to the
rate of change of current, which has units ofhenries (H). Inductors have
values that typically range from 1 µH (10-6H) to 1 H. Many inductors have a
magnetic coremade of iron or ferrite inside the coil, which serves to
increase the magnetic field and thus the inductance. Along withcapacitors
and resistors, inductors are one of the three passive linear circuit elements
that make up electric circuits. Inductors are widely used in alternating
current (AC) electronic equipment, particularly in radio equipment. They are
used to block the flow of AC current while allowing DC to pass; inductors
designed for this purpose are called chokes. They are also used in
electronic filters to separate signals of different frequencies, and in
combination with capacitors to make tuned circuits, used to tune radio and
TV receivers.
40
41