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Electronic Devices by Floyd
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Chapter by chapter summary of Electronic Devices by Floyd 9th Edition
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Chapter 1 Summary (Introduction to Semiconductors)• According to the classical Bohr model, the atom is viewed as having a
planetary-type structure with electrons orbiting at various distances around the central
nucleus.
• The nucleus of an atom consists of protons and neutrons. The protons have a positive
charge and the neutrons are uncharged. The number of protons is the atomic number
of the atom.
• Electrons have a negative charge and orbit around the nucleus at distances that
depend on their energy level. An atom has discrete bands of energy called shells in
which the electrons orbit. Atomic structure allows a certain maximum number of
electrons in each shell. These shells are designated 1, 2, 3, and so on. In their natural
state, all atoms are neutral because they have an equal number of protons and
electrons.
• The outermost shell or band of an atom is called the valence band, and electrons that
orbit in this band are called valence electrons. These electrons have the highest energy
of all those in the atom. If a valence electron acquires enough energy from an outside
source such as heat, it can jump out of the valence band and break away from its atom.
• Insulating materials have very few free electrons and do not conduct current at all
under normal circumstances. Semiconductive materials fall in between conductors and
insulators in their ability to conduct current.
• Materials that are conductors have a large number of free electrons and conduct
current very well.
• Semiconductor atoms have four valence electrons. Silicon is the most widely used
semiconductive material.
• Semiconductor atoms bond together in a symmetrical pattern to form a solid material
called a crystal. The bonds that hold a crystal together are called covalent bonds.
Within the crystal structure, the valence electrons that manage to escape from their
parent atom are called conduction electrons or free electrons. They have more energy
than the electrons in the valence band and are free to drift throughout the material.
• When an electron breaks away to become free, it leaves a hole in the valence band
creating what is called an electron-hole pair. These electron-hole pairs are thermally
produced because the electron has acquired enough energy from external heat to break
away from its atom.
• A free electron will eventually lose energy and fall back into a hole. This is called
recombination. But, electron-hole pairs are continuously being thermally generated so
there are always free electrons in the material.
• When a voltage is applied across the semiconductor, the thermally produced free
electrons move in a net direction and form the current. This is one type of current in
an intrinsic (pure) semiconductor.
,• Another type of current is the hole current. This occurs as valence electrons move
from hole to hole creating, in effect, a movement of holes in the opposite direction.
• An n-type semi-conductive material is created by adding impurity atoms that have
five valence electrons. These impurities are pentavalent atoms. A p-type
semiconductor is created by adding impurity atoms with only three valence electrons.
These impurities are trivalent atoms.
• The process of adding pentavalent or trivalent impurities to a semiconductor is called
doping.
• The majority carriers in an n-type semiconductor are free electrons acquired by the
doping process, and the minority carriers are holes produced by thermally generated
electron-hole pairs. The majority carriers in a p-type semiconductor are holes acquired
by the doping process, and the minority carriers are free electrons produced by
thermally generated electron-hole pairs.
• A pn junction is formed when part of a material is doped n-type and part of it is
doped p-type. A depletion region forms starting at the junction that is devoid of any
majority carriers. The depletion region is formed by ionization.
• The barrier potential is typically 0.7 V for a silicon diode and 0.3 V for germanium.
• There is current through a diode only when it is forward-biased. Ideally, there is no
current when there is no bias nor when there is reverse bias. Actually, there is a very
small current in reverse bias due to the thermally generated minority carriers, but this
can usually be neglected.
• Avalanche occurs in a reverse-biased diode if the bias voltage equals or exceeds the
breakdown voltage.
• A diode conducts current when forward-biased and blocks current when
reversed-biased.
• Reverse breakdown voltage for a diode is typically greater than 50 V.
• An ideal diode presents an open when reversed-biased and a short when
forward-biased.
• The V-I characteristic curve shows the diode current as a function of voltage across
the diode.
• The resistance of a forward-biased diode is called the dynamic or ac resistance.
• Reverse current increases rapidly at the reverse breakdown voltage.
• Reverse breakdown should be avoided in most diodes.
• The ideal model represents the diode as a closed switch in forward bias and as an
open switch in reverse bias.
• The practical model represents the diode as a switch in series with the barrier
potential.
• The complete model includes the dynamic forward resistance in series with the
practical model in forward bias and the reverse resistance in parallel with the open
switch in reverse bias.
, • Many DMMs provide a diode test function.
• DMMs display the diode drop when the diode is operating properly in forward bias.
• Most DMMs indicate “OL” when the diode is open.
Chapter 2 Summary (Diode Applications)
• The single diode in a half-wave rectifier is forward-biased and conducts for 180º of
the input cycle.
• The output frequency of a half-wave rectifier equals the input frequency.
• PIV (peak inverse voltage) is the maximum voltage appearing across the diode in
reverse bias.
• Each diode in a full-wave rectifier is forward-biased and conducts for 180º of the
input cycle.
• The output frequency of a full-wave rectifier is twice the input frequency.
• The two basic types of full-wave rectifier are center-tapped and bridge.
• The peak output voltage of a center-tapped full-wave rectifier is approximately
one-half of the total peak secondary voltage less one diode drop.
• The PIV for each diode in a center-tapped full-wave rectifier is twice the peak output
voltage plus one diode drop.
• The peak output voltage of a bridge rectifier equals the total peak secondary voltage
less two diode drops.
• The PIV for each diode in a bridge rectifier is approximately half that required for an
equivalent center-tapped configuration and is equal to the peak output voltage plus
one diode drop.
• A capacitor-input filter provides a dc output approximately equal to the peak of its
rectified input voltage.
• Ripple voltage is caused by the charging and discharging of the filter capacitor.
• The smaller the ripple voltage, the better the filter.
• Regulation of output voltage over a range of input voltages is called input or line
regulation.
• Regulation of output voltage over a range of load currents is called load regulation.
• Diode limiters cut off voltage above or below specified levels. Limiters are also
called clippers.
• Diode clampers add a dc level to an ac voltage.
• A dc power supply typically consists of an input transformer, a diode rectifier, a
filter, and a regulator.
• Voltage multipliers are used in high-voltage, low-current applications such as for
electron beam acceleration in CRTs and for particle accelerators.
• A voltage multiplier uses a series of capacitor/diode stages.
• Input voltage can be doubled, tripled, or quadrupled.
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