Download Electronic Conditioners

Electronic Conditioners
Unit 11
Objectives
1.
2.
3.
4.
5.
Describe basic semiconductor theory.
Describe basic transistor theory.
Describe an IC.
Describe how an op-amp works.
Describe how an audio-transformer works.
An electronic conditioner is any device that conditions or changes a voltage
or wave form. Many electronic conditioners can be found in everyday life in
radios, microwave ovens, automobiles and airplanes. Electronic conditioners
include transistors, diodes, regulators, op-amps, audio-transformers, and
integrated circuits (IC’s).
In modern society we take these components for granted, yet we could not
function without them.
Basic semiconductor theory has existed since the 1930’s. But the transistor
was not invented until the late 1940s because manufacturing technology had
not sufficiently advanced until then. The first transistor was invented by John
Bardeen, William Shockley, and Walter Brattain at Bell Labs in New Jersey.
The invention won the trio a Nobel Prize in Physics.
To understand semiconductors, you must first recall what you already
learned about atoms. An atom consists of a nucleus made of protons
and neutrons, surrounded by electrons that orbit the nucleus. The
number of protons and electrons in an atom are equal. The electrons
have negative charges that are equal to the positive charges of the
protons in the nucleus. This balance permits electroneutrality , which
means the positive and negative charges are exactly balanced and the
atom has no net charge or is neutral.
The electrons of an atom
move around the nucleus in
paths called energy levels.
Not all electrons in an atom
share the same energy level.
For example, an oxygen atom
has 8 protons in its nucleus
and 8 electrons orbiting the
nucleus with 2 of its electrons
in the first energy level and 6
electrons in its second energy
level.
You can compare the energy levels of an atom to steps on a staircase.
An electron can be on one step or the next, but not in-between steps.
When an electron absorbs energy, it moves to a higher energy level, or
one farther from the nucleus. When an electron loses energy, it falls to
a lower energy level.
The flow of electricity through a material depends on the electrons in
the outer energy level of the atoms. These electrons are called valence
electrons. The valence electrons in a metal are not held tightly to the
nuclei of their atoms, but are free to move in the material. That is why
metals are good conductors. The valence electrons in insulators, such
as glass and rubber, are tightly bound to nuclei of their atoms.
Whether a substance is classified as a conductor or insulator depends
on how tightly the nuclei of their atoms hold their electrons. Some
materials, such as silicon and germanium, are good insulators in their
pure crystalline form. But these materials increase in conductivity
tremendously when a tiny amount of impurity is added that adds or
removes an electron from their crystal structure. This process is called
doping. For this reason, silicon and germanium are classified as
semiconductors. Semiconductors are used in the manufacturing of
transistors, IC’s and diodes.
Germanium has 32 protons in
its nucleus and 32 electrons
orbiting in four energy levels
(see Figure ->). The innermost
energy level has 2 electrons,
the second energy level has 8
electrons, and the third
energy level has 18 electrons,
and the outer energy level
has 4 electrons (valance
electrons). Germanium’s
outer most level is not stable
because this energy level can
hold 8 electrons.
Silicon has 14 protons in
its nucleus and 14
electrons orbiting in
three energy levels (see
Figure). The innermost
energy level has 2
electrons, the second
energy level has 8
electrons and the third
energy level had 4
electrons (valance
electrons).
Notice that both germanium and silicon have 4 valence electrons.
Because of this, they are called tetravalent elements. Tetravalent
elements will try to assume a stable configuration (8 valence electrons)
by forming bonds with adjoining atoms, where they share valence
electrons. A cluster of silicon or germanium atoms sharing valence
electrons forms a regular arrangement called a crystal.
A tetravalent material can be doped with a pentavalent ( 5 valence
electrons) material, such as phosphorus, arsenic, or antimony. A
phosphorus atom in a cluster of silicon atoms donates an extra
electron. This extra electron can move through the crystal with ease.
This allows the material to carry an electric charge. A material doped
with a pentavalent material is an n-type semiconductor. The “n” stands
for “negative” which is the charge resulting from extra electron.
If the tetravalent material is doped with a trivalent (3 valence
electrons) material, such as boron, a p-type semiconductor is formed.
The “p” stand for “positive” which is the charge resulting from a
shortage of one electron. A boron atom in a cluster of silicon leaves a
vacant electron called a hole. An electron from a nearby atom can
move into the hole, thus causing the hole to move to a new location. In
a p-type semiconductor the holes carry the electric current.
Both n-type and p-type semiconductors conduct electric current. The
resistance of both types is determined by the proportion of excess
electrons or holes, so both types can function as resistors and can
conduct current in any direction.
The P-N junction is the interface between a p-type and an n-type
material and is the basic design of the unbiased diode, A diode can be
forward-biased where it can conduct or reverse-biased where it cannot
conduct.
When the charge from a battery repels holes toward the P-N junction,
electrons will cross the junction and combine with the holes and a
current will flow. The diode is then forward-biased. When the charge
from the battery attracts holes and electrons away from the P-N
junction, no current can flow, The diode is then reversed-biased.
Transistors
Transistors are semiconductor devices with three small leads. A very
small current or voltage at one lead can control a much larger current
flowing through the other two leads. This means that transistors can be
used as amplifiers and switches.
Transistors make our electronics world go ‘round. They’re critical as a control
source in just about every modern circuit. Sometimes you see them, but moreoften-than-not they’re hidden deep within the die of an integrated circuit. In this
lesson we’ll introduce you to the basics of the most common transistor around: the
bi-polar junction transistor (BJT).
A transistor is basically modeled after a pair of P-N junction diodes connected
together. These transistors have three divisions or segments: the emitter, the base
and the collector. The base is very thin and contains fewer doping atoms than the
emitter and collector. Thus a very small emitter-base current will cause a much
larger emitter-collector current to flow. Transistors are built by stacking three
different layers of semiconductor material together. Some of those layers have
extra electrons added to them (a process called “doping”), and others have
electrons removed (doped with “holes” – the absence of electrons). A
semiconductor material with extra electrons is called an n-type (n for negative
because electrons have a negative charge) and a material with electrons removed is
called a p-type (for positive). Transistors are created by either stacking an n on top
of a p on top of an n, or p over n over p. In both cases, the base ( the middle
segment) acts like a gate that controls the current moving through the three parts.
Because the emitter-collector current is up to several hundred times
greater than the emitter-base current, the transistor acts as a efficient
current amplifier. For example, a small current generated by a voice
directed towards a microphone is applied to the base of a transistor.
The small base current controls the much larger emitter-collector
current that is applied to the terminals of a loudspeaker, which emits a
greatly amplified sound.
It is important to know that in a silicon transistor, the base-emitter
junction will not conduct current until the forward voltage exceeds 0.6
volts. It is also important to know that too much current will cause a
transistor to become hot and not properly operate correctly. Too much
current or voltage can damage or destroy the transistor. The transistors
in the MB100 Kit are protected so that they can not be damaged.
Integrated Circuits
Integrated circuits (IC’s) are made by forming individual transistors, diodes and
resistors on small silicon chips (see Figure below). The components are connected
to one another with aluminum “wires” deposited on the chip. Integrated circuits
can contain few transistors or they can contain thousands of transistors. One kind
of integrated circuit contains over 260,000 transistors on a silicon chip that is only
about a quarter-inch square. By 1991, chips with 4 million transistors were being
produced and 2011, 3.9 billion transistors in a single IC.
Operational Amplifiers
Operational amplifiers (op-amps) are devices which are versatile
integrated chips. They are called “operational” because they were
originally designed to do mathematical operations. Analog computers
use op-amps to solve complex equations. Op-amps are used in
applications ranging from monitoring the faint electrical impulses
produced by living organisms to comparing the magnitude of two
signals and indicating which is larger. Op-amps designed to produce an
output voltage that is an amplified but faithful copy of input voltage.
Audio- Transformers
Audio-transformers are devices that have the ability to transform
voltage and current to higher or lower levels. They are used to match
the impedance (opposition to the flow of alternating current) of an
amplifier to that of a microphone, speaker or other device. Step-up
audio-transformers can be used to increase the power. In either case,
the audio-transformer isolates and supplies the output section with a
constant load, Audio-transformers are used in intercom systems and
televisions sets.