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Basic Electrical Components
There are several important basic electrical components that are
commonly found in the circuits of virtually all PC
parts and peripherals. These devices are the fundamental
building blocks of electrical and electronic circuits, and can
be found in great numbers on motherboards, hard disk logic
boards, video cards and just about everywhere else in
the PC, including places that might surprise you. They can be
used and combined with each other and dozens of
other devices, in so many different ways that I could not even
begin to describe them all. Still, it is useful to know abit about
how they work, and this page will at least provide you with a basis
for recognizing some of what you see
on those boards, and perhaps understanding the fundamentals of
circuit schematics. Bear in mind when reading the
descriptions below that it would really take several full pages
to fully describe the workings of most of these
components! Fortunately, this level of detail isn't really
necessary to provide the background necessary whenworking with
PCs.
Battery: A direct current electricity source of a specific
voltage, used primarily in smallcircuits.
Resistor: As you could probably guess from the name, a resistor
increases the resistance of a
circuit. The main purpose of this is to reduce the flow of
electricity in a circuit. Resistors
come in all different shapes and sizes. They dissipate heatas a
result of their opposingelectricity, and are therefore rated both
in terms of their resistance (how much they
oppose the flow of electrons) and their power capacity (how much
power they can
dissipate before becoming damaged.) Generally, bigger resistors
can handle more power.There are also variable resistors, which can
have their resistance adjusted by turning a
knob or other device. These are sometimes called
potentiometers.
Capacitor: A capacitor is a component made from two (or two sets
of) conductive plates withan insulator between them. The insulator
prevents the plates from touching. When a DC
current is applied across a capacitor, positive charge builds on
one plate (or set of plates)
and negative charge builds on the other. The charge will remain
until the capacitor isdischarged. When an AC current is applied
across the capacitor, it will charge one set of
plates positive and the other negative during the part of the
cycle when the voltage is
positive; when the voltage goes negative in the second half of
the cycle, the capacitor willrelease what it previously charged,
and then charge the opposite way. This then repeats
for each cycle. Since it has the opposite charge stored in it
each time the voltage changes,
it tends to oppose the change in voltage. As you can tell then,
if you apply a mixed DC
and AC signal across a capacitor, the capacitor will tend to
block the DC and let the ACflow through. The strength of a
capacitor is called capacitance and is measured infarads
(F). (In practical terms, usually microfarads and the like,
since one farad would be a very
large capacitor!) They are used in all sorts of electronic
circuits, especially combinedwith resistors and inductors, and are
commonly found in PCs.
Inductor: An inductor is essentially a coil of wire. When
current flows through an inductor, a
magnetic field is created, and the inductor will store this
magnetic energy until it is
released. In some ways, an inductor is the opposite of a
capacitor. While a capacitorstores voltage as electrical energy, an
inductor stores current as magnetic energy. Thus, a
capacitor opposes a change in the voltage of a circuit, while an
inductor opposes a change
in its current. Therefore, capacitors block DC current and let
AC current pass, whileinductors do the opposite. The strength of an
inductor is called--take a wild guess--its
inductance, and is measured in henrys (H). Inductors can have a
core of air in the middle
of their coils, or a ferrous (iron) core. Being a magnetic
material, the iron core increases
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the inductance value, which is also affected by the material
used in the wire, and the
number of turns in the coil. Some inductor cores are straight in
shape, and others are
closed circles called toroids. The latter type of inductor is
highly efficient because theclosed shape is conducive to creating a
stronger magnetic field. Inductors are used in all
sorts of electronic circuits, particularly in combination with
resistors and capacitors, and
are commonly found in PCs.Transformer: A transformer is an
inductor, usually with an iron core, that has two lengths of
wire wrapped around it instead of one. The two coils of wire do
not electrically connect,
and are normally attached to different circuits. One of the most
important components inthe world of power, it is used to change one
AC voltage into another. As described above,
when a coil has a current passed through it, a magnetic field is
set up proportional to the
number of turns in the coil. This principle also works in
reverse: if you create a magneticfield in a coil, a current will be
induced in it, proportional to the number of turns of the
coil. Thus, if you create a transformer with say, 100 turns in
the first orprimary coil, and
50 turns in the second orsecondary coil, and you apply 240 VAC
to the first coil, acurrent of 120 VAC will be induced in the
second coil (approximately; some energy is
always lost during the transformation). A transformer with more
turns in its primary thanits secondary coil will reduce voltage and
is called a step-down transformer. One with
more turns in the secondary than the primary is called a step-up
transformer.Transformers are one of the main reasons we use AC
electricity in our homes and not
DC: DC voltages cannot be changed using transformers. They come
in sizes ranging from
small ones an inch across, to large ones that weigh hundreds of
pounds or more,depending on the voltage and current they must
handle.
Diode / LED: A diode is a device, typically made from
semiconductor material, that restricts
the flow of current in a circuit to only one direction; it will
block the bulk of any current
that tries to go "against the flow" in a wire. Diodes have a
multitude of uses. Forexample, they are often used in circuits that
convert alternating current to direct current,
since they can block half the alternating current from passing
through. A variant of thecommon diode is the light-emitting diode
orLED; these are the most well-known andcommonly-encountered kind
of diode, since they are used on everything from keyboards
to hard disks to television remote controls. An LED is a diode
that is designed to emit
light of a particular frequency when current is applied to it.
They are very useful as statusindicators in computers and
battery-operated electronics; they can be left on for hours or
days at a time because they run on DC, require little power to
operate, generate very little
heat and last for many years even if run continuously. They are
now even being madeinto low-powered, long-operating
flashlights.
Fuse: A fuse is a device designed to protect other components
from accidental damage due to
excessive current flowing through them. Each type of fuse is
designed for a specific
amount of current. As long as the current in the circuit is kept
below this value, the fusepasses the current with little
opposition. If the current rises above the rating of the fuse--
due to a malfunction of some sort or an accidental
short-circuit--the fuse will "blow" and
disconnect the circuit. Fuses are the "heroes" of the
electronics world, literally burning upor melting from the high
current, causing a physical gap in the circuit and saving other
devices from the high current. They can then be replaced when
the problem condition has
been corrected. All fuses are rated in amps for the amount of
current they can toleratebefore blowing; they are also rated for
the maximum voltage they can tolerate. Always
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