Semiconductor Devices and Circuits
sec.1-1 d 3 kinds of
4mulas
a defi nition is a 4mula invented 4
a new concept.A law is a 4mula 4
a rel8on in nature.A deriv8on is a
4mula produced with mathem8cs.
sec.1-2 approxim8ons
approxim8ons r widely used in
d electronics industry.D ideal
approxim8on is useful 4 troubleshooting.
d 2nd approxim8on
is useful 4 preliminary circuit calcul8ons.
higher approxim8ons r
used with computers.
sec.1-3 voltage sources
an ideal voltage source hs no internal
resistance.
D 2nd approxim8on
of a voltage source hs an internal
resistance in series with d source.A
stiff voltage source is defi ned as 1
whose internal resistance is less than
1?100 of d load resistance.
sec.1-4 current sources
an ideal current source hs an infi nite
internal resistance.D 2nd approxim8on
of a current source hs
a large internal resistance in parallel
with d source.A stiff current source
is defi ned as 1 whose internal resistance
is more than 100 times d
load resistance.
sec.1-5 thevenins theorem
d thevenin voltage is defi ned as
d voltage across an open load.D
thevenin resistance is defi ned as
d resistance an ohmmeter would
measure with an open load & ol
sources reduced 2 zero.Thevenin
proved dat a thevenin equivalent
circuit will produce d same load current
as ne other circuit with sources
& linear resistances.
sec.1-6 nor2ns theorem
d nor2n resistance equals d
thevenin resistance.D nor2n
current equals d load current
wen d load is shorted.Nor2n
proved dat a nor2n equivalent circuit
produces d same load voltage
as ne other circuit with sources &
linear resistances.Nor2n current
equals thevenin voltage divided by
thevenin resistance.
sec.1-7 troubleshooting
d most common troubles r
shorts,opens,& intermittent troubles.
a short always hs zero voltage
across it;d current thru a short
must b calcul8d by examining
d rest of d circuit.An open always
hs zero current thru it;
d voltage across an open must b
calcul8d by examining d rest of
d circuit.An intermittent trouble is
an on-again,off -again trouble dat
requires p8ent & logical troubleshooting
2 isol8 it.
sec.2-1 conduc2rs
a neutral copper a2m hs only 1
electron in its outer orbit.Since dis
single electron can b easily dislodged
frm its a2m,it is called a
free electron.copper is a gud conduc2r
coz d slightest voltage
causes free electrons 2 fl ow frm
1 a2m 2 d next.
sec.2-2 semiconduc2rs
silicon is d most widely used
semiconduc2r m8rial.An isol8d
silicon a2m hs 4 electrons in its
outer,or valence,orbit.D #
of electrons in d valence orbit is
d key 2 conductivity.Conduc2rs
have 1 valence electron,semiconduc2rs
have 4 valence electrons,
& insula2rs have 8 valence
electrons.
sec.2-3 silicon crystals
each silicon a2m in a crystal hs
its 4 valence electrons plus 4
more electrons dat R shared by
d neighboring a2ms.@ room temperature,
a pure silicon crystal hs only a few
thermally produced free
electrons & holes.D amount
of time btwn d cre8on &
recombin8on of a free electron
& a hole is called d lifetime.
sec.2-4 intrinsic
semiconduc2rs
an intrinsic semiconduc2r is a pure
semiconduc2r.Wen an external
voltage is applied 2 d intrinsic
semiconduc2r,d free electrons
fl ow 2ward d positive battery
terminal & d holes fl ow 2ward
d neg8ve battery terminal.
Sec.2-5
2 types
of flow
2 types of carrier fl ow exist in an
intrinsic semiconduc2r.1st,there
is d fl ow of free electrons thru
larger orbits (conduction band).
2nd,there is d fl ow of holes
thru smaller orbits (valence
band).
sec.2-6 doping a
semiconduc2r
doping increases d conductivity
of a semiconduc2r.A doped
semiconduc2r is called an extrinsic
semiconduc2r.wen an intrinsic
semiconduc2r is doped with pentavalent
(donor) a2ms,it hs more
free electrons than holes.Wen an
intrinsic semiconduc2r is doped with
trivalent (accep2r) a2ms,it hs more
holes than free electrons.
Sec.2-7
2 types
of extrinsic
semiconduc2rs
in an n-type semiconduc2r,d free
electrons R d majority carriers,&
d holes R d minority carriers.In
a p-type semiconduc2r,d holes
R d majority carriers,& d free
electrons R d minority carriers.
sec.2-8 d unbiased
diode
an unbiased diode hs a depletion
layer @ d pn junction.D ions in
dis depletion layer produce a barrier
potential.@ room temperature,dis
barrier potential is approxim8ly
0.7 v 4 a silicon diode & 0.3 v 4
a germanium diode.
Sec.2-9
4ward bias
wen an external voltage opposes d
barrier potential,d diode is 4wardbiased.
if d applied voltage is gre8r
than d barrier potential,d current
is large.In other words,current fl ows
easily in a 4ward-biased diode.
sec.2-10 reverse bias
wen an external voltage aids
d barrier potential,d diode is
reverse-biased.D width of d
depletion layer increases wen d
reverse voltage increases.D current
is approxim8ly zero.
sec.2-11 breakdown
2o much reverse voltage will produce
either avalanche or zener eff ect.
then,d large breakdown current
destroys d diode.In general,diodes
R never oper8d in d breakdown
region.D only exception is d
zener diode,a special-purpose diode
discussed in a l8r chapter.
sec.2-12 energy levels
d larger d orbit,d higher d
energy level of an electron.If an
outside 4ce raises an electron 2 a
higher energy level,d electron will
emit energy wen it falls back 2 its
original orbit.
sec.2-13 barrier potential
& temperature
wen d junction temperature
increases,d depletion layer
becomes narrower & d barrier
potential decreases.It will decrease
approxim8ly 2 mv 4 each degree
celsius increase.
sec.2-14 reverse-biased
diode
there R 3 comp1nts of
reverse current in a diode.1st,
there is d transient current dat
occurs wen d reverse voltage
changes.2nd,there is d
minority-carrier current,also called
d satur8on current coz it is
independent of d reverse voltage.
3rd,there is d surface-leakage
current.It increases wen d
reverse voltage increases.
SEC. 3-1
BASIC IDEAS
A diode is a nonlinear device. The
knee voltage, approximately 0.7 V
for a silicon diode, is where the forward
curve turns upward. The bulk
resistance is the ohmic resistance
of the p and n regions. Diodes have
a maximum forward current and a
power rating.
SEC. 3-2
THE IDEAL DIODE
This is the fi rst approximation of a
diode. The equivalent circuit is a
switch that closes when forward
biased and opens when reverse
biased.
SEC. 3-3
THE SECOND
APPROXIMATION
In this approximation, we visualize
a silicon diode as a switch in series
with a knee voltage of 0.7 V. If the
Thevenin voltage facing the diode is
greater than 0.7 V, the switch closes.
SEC. 3-4
THE THIRD
APPROXIMATION
We seldom use this approximation
because bulk resistance is usually
small enough to ignore. In this approximation,
we visualize the diode
as a switch in series with a knee voltage
and a bulk resistance.
SEC. 3-5
TROUBLESHOOTING
When you suspect that a diode is
the trouble, remove it from the circuit
and use an ohmmeter to measure
its resistance in each direction. You
should get a high resistance one
way and a low resistance the other
way, at least 1000:1 ratio. Remember
to use a high enough resistance
range when testing a diode to avoid
possible diode damage. A DMM will
display 0.50.7 V when a diode is
forward biased and an overrange
indication when it is reverse biased.
SEC. 3-6
READING A DATA
SHEET
Data sheets are useful to a circuit
designer and may be useful to a
repair technician when selecting
a substitute device, which is
sometimes required. Diode data
sheets from diff erent manufacturers
contain similar information, but
diff erent symbols are used to indicate
diff erent operating conditions.
Diode data sheets may list the
following: breakdown voltage
(VR, VRRM, VRWM, PIV, PRV, BV),
maximum forward current
(IF(max
), IF(av), I0), forward voltage drop
(VF(max), VF), and maximum reverse
current (IR(max), IRRM).
SEC. 3-7
HOW TO CALCULATE
BULK RESISTANCE
You need two points in the forward
region of the third approximation.
One point can be 0.7 V with zero
current. The second point comes
from the data sheet at a large forward
current where both a voltage and a
current are given.
SEC. 3-8
DC RESISTANCE OF
A DIODE
The dc resistance equals the diode
voltage divided by the diode current
at some operating point. This
resistance is what an ohmmeter will
measure. DC resistance has limited
application, aside from telling you that
it is small in the forward direction and
large in the reverse direction.
SEC. 3-9
LOAD LINES
The current and voltage in a diode
circuit have to satisfy both the diode
curve and Ohms law for the load
resistor. These are two separate requirements
that graphically translate
to the intersection of the diode curve
and the load line.
SEC. 3-10
SURFACE-MOUNT
DIODES
Surface-mount diodes are often
found on modern electronics circuits
boards. These diodes are small, effi –
cient, and typically found either as an
SM (surface-mount) or an SOT (small
outline transistor) case style.
SEC. 3-11
INTRODUCTION
TO ELECTRONIC
SYSTEMS
Semiconductor components are
combined to form circuits. Circuits
can be combined to become functional
blocks. Functional blocks can
be interconnected to form electronic
systems.
SEC. 4-1
THE HALF-WAVE
RECTIFIER
The half-wave rectifi er has a diode
in series with a load resistor. The
load voltage is a half-wave output.
The average or dc voltage out of a
half-wave rectifi er equals 31.8 percent
of the peak voltage.
SEC. 4-2
THE TRANSFORMER
The input transformer is usually a
step-down transformer in which the
voltage steps down and the current
steps up. The secondary voltage
equals the primary voltage divided
by the turns ratio.
SEC. 4-3
THE FULL-WAVE
RECTIFIER
The full-wave rectifi er has a centertapped
transformer with two diodes
and a load resistor. The load voltage
is a full-wave signal whose peak
value is half the secondary voltage.
The average or dc voltage out of a
full-wave rectifi er equals 63.6 percent
of the peak voltage, and the
ripple frequency equals 120 Hz
instead of 60 Hz.
SEC. 4-4
THE BRIDGE
RECTIFIER
The bridge rectifi er has four diodes.
The load voltage is a full-wave signal
with a peak value equal to the secondary
voltage. The average or dc
voltage out of a half-wave rectifi er
equals 63.6 percent of the peak voltage,
and the ripple frequency equals
120 Hz.
SEC. 4-5
THE CHOKE-INPUT
FILTER
The choke-input fi lter is an LC voltage
divider in which the inductive
reactance is much greater than the
capacitive reactance. The type of
fi lter allows the average value of the
rectifi ed signal to pass through to the
load resistor.
SEC. 4-6
THE CAPACITORINPUT
FILTER
This type of fi lter allows the peak
value of the rectifi ed signal to pass
through to the load resistor. With a
large capacitor, the ripple is small,
typically less than 10 per cent of
the dc voltage. The capacitor-input
fi lter is the most widely used fi lter in
power supplies.
SEC. 4-7
PEAK INVERSE
VOLTAGE AND SURGE
CURRENT
The peak inverse voltage is the
maximum voltage that appears
across the nonconducting diode of
a rectifi er circuit. This voltage must
be less than the breakdown voltage
of the diode. The surge current is
the brief and large current that exists
when the power is fi rst turned on.
It is brief and large because the fi lter
capacitor must charge to the peak
voltage during the fi rst cycle or, at
most, during the fi rst few cycles.
SEC. 4-8
OTHER POWERSUPPLY
TOPICS
Real transformers usually specify the
secondary voltage at a rated load
current. To calculate the primary
current, you can assume that the
input power equals the output
power. Slow-blow fuses are typically
used to protect against the surge
current. The average diode current
in a half-wave rectifi er equals the
dc load current. In a full-wave or
bridge rectifi er, the average current
in any diode is half the dc load
current. RC fi lters and LC fi lters may
occasionally be used to fi lter the
rectifi ed output.
SEC. 4-9 TROUBLESHOOTING
Some of the measurements that can
be made with a capacitor-input fi lter
are the dc output voltage, the primary
voltage, the secondary voltage,
and the ripple. From these, you can
usually deduce the trouble. Open
diodes reduce the output voltage
to zero. An open fi lter capacitor
reduces the output to the average
value of the rectifi ed signal.
SEC. 4-10
CLIPPERS AND
LIMITERS
A clipper shapes the signal. It clips
off positive or negative parts of the
signal. The limiter or diode clamp
protects sensitive circuits from too
much input.
SEC. 4-11
CLAMPERS
The clamper shifts a signal positively
or negatively by adding a dc voltage
to the signal. The peak-to-peak detector
produces a load voltage equal
to the peak-to-peak value.
SEC. 4-12
VOLTAGE
MULTIPLIERS
The voltage doubler is a redesign
of the peak-to-peak detector. It uses
rectifi er diodes instead of smallsignal
diodes. It produces an output
equal to two times the peak value of
the rectifi ed signal. Voltage triplers
and quadruplers multiply the input
peak by factors of 3 and 4. Very high
voltage power supplies are the main
use of voltage multipliers.
SEC. 5-1
THE ZENER DIODE
This is a special diode optimized for
operation in the breakdown region.
Its main use is in voltage regulators
circuits that hold the load voltage
constant. Ideally, a reverse-biased
zener diode is like a perfect battery.
To a second approximation, it has a
bulk resistance that produces a small
additional voltage.
SEC. 5-2
THE LOADED ZENER
REGULATOR
When a zener diode is in parallel with
a load resistor, the current through
the current-limiting resistor equals
the sum of the zener current and the
load current. The process for analyzing
a zener regulator consists of fi nding
the series current, load current,
and zener current (in that order).
SEC. 5-3
SECOND
APPROXIMATION
OF A ZENER DIODE
In the second approximation, we visualize
a zener diode as a battery of
VZ and a series resistance of RZ. The
current through RZ produces an additional
voltage across the diode, but
this voltage is usually small. You need
zener resistance in order to calculate
ripple reduction.
SEC. 5-4
ZENER DROP-OUT
POINT
A zener regulator will fail to regulate
if the zener diode comes out of
breakdown. The worst-case conditions
occur for minimum source
voltage, maximum series resistance,
and minimum load resistance. For
the zener regulator to work properly
under all operating conditions, there
must be zener current under the
worst-case conditions.
SEC. 5-5
READING A DATA
SHEET
The most important quantities on the
data sheet of zener diodes are the
zener voltage, the maximum power
rating, the maximum current rating,
and the tolerance. Designers also
need the zener resistance, the
derating factor, and a few other
items.
SEC. 5-6
TROUBLESHOOTING
Troubleshooting is an art and a science.
Because of this, you can learn
only so much from a book. The rest
has to be learned from direct experience
with circuits in trouble. Because
troubleshooting is an art, you have
to ask What if? Often and feel your
way to a solution.
SEC. 5-7
LOAD LINES
The intersection of the load line and
the zener diode graph is the Q point.
When the source voltage changes,
a diff erent load line appears with a
diff erent Q point. Although the two Q
points may have diff erent currents,
the voltages are almost identical.
This is a visual demonstration of voltage
regulation.
SEC. 5-8
LIGHT-EMITTING
DIODES (LEDS)
The LED is widely used as an indicator
on instruments, calculators, and
other electronic equipment. Highintensity
LEDs off er high luminous
effi cacy (lm/W) and are fi nding their
way into many applications.
SEC. 5-9
OTHER OPTOELECTRONIC
DEVICES
By combining seven LEDs in a package,
we get a seven-segment indicator.
Another important optoelectronic
device is the optocoupler, which
allows us to couple a signal between
two isolated circuits.
SEC. 5-10
THE SCHOTTKY
DIODE
The reverse recovery time is the
time it takes a diode to shut off