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ELECTRONICS
BASIC
OF3 COMPONENTS
POSTVENTAFORMACION
Service
BASIC SELF-STUDY MANUALS
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No part of this document may be reproduced or transmitted in any form or by any means, electronic, mechanical, photocopyng, recording, or
otherwise without the prior written permission of the copyright holders.
TITLE: Basic Components of Electronics B.M. No 3 - AUTHOR: Service Organisation - SEAT, S.A. Zona Franca, Calle 2Register of business names Barcelona. Volume 23662, Folio 1, Page 56855
1st edition - PUBLICATION DATE: April 97 - LEGAL REGISTER: B. 4508-98Preprinting and printing: TECFOTO, S.L. - Ciutat de Granada, 55 - 08005 Barcelona - Desing and Composition: WIN&KEN
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C O N T E N T S
PASSIVE COMPONENTS:FIXED RESISTORS 4-5
PASSIVE COMPONENTS:
VARIABLE RESISTORS 6-9
PASSIVE COMPONENTS:
THE CAPACITOR 10-13
ACTIVE COMPONENTS 14-15
ACTIVE COMPONENTS:
THE DIODE 16-19
ACTIVE COMPONENTS:
ZENER DIODE, LED, PHOTODIODE 20-21
ACTIVE COMPONENTS:
THE TRANSISTOR 22-23
APPLICATIONS OF TRANSISTORS 24-25
ACTIVE COMPONENTS:
THE THYRISTOR, PHOTOTRANSISTOR,TRIAC AND DIAC 26-27
INTEGRATED CIRCUITS 28-29
SELF-CHECK EXERCISES 30-33
Dear reader, to facilitate your understanding
of this manual we recommend that you
revise edition number ONE from this
series with the title: BASIC CONCEPTS OF
ELECTRICI TY.
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Construction andoperation
Resistors are passive
components used to reduce the
current flowing in a circuit, or as
voltage dividers which permit
the voltage to be adjusted in a
specific point in the circuit to a
set value.
Using the hydraulic analogy, the
resistors could be compared to
the length, section and shape of
tubes through which water
flows; according to these char-
acteristics the flow will be
restricted to a greater or lesser
extent, thus loosing part of its
energy.
The resistors placed in a circuit
cause a “drop” in voltage
between their ends when
current flows through, this drop
is proportional to the value of
the resis tor.
They are made from materials
with a high specific resistance
value (for example coiled wire,
carbon or metallic foil), thus
obtaining the desired ohm value
in a small dimensioned
component.
The most common resistors are
made from carbon. These are
formed by a cylindrical ceramic
body with a carbon coating. The
resistance value is set by a
carbon winding process or by
varying the thickness of the
carbon coating.
The metallic foil resistors are
based on a ceramic substrate on
which a fine layer made of a
mixture of metals and resins is
deposited; the resistance value
PA S S I V E CO M P O N E N T S :F I X E D RE S I S T O R S
“All electronic circuits are made up not only of semiconductors but
also from a series of passive components which are essential to the
operation of any circuit, these so called passive components are:
resistors, potentiometers and capacitors”.
B3-02
LAYOUT OF A RESISTOR
Covering
Metallic terminalCarbon coating
Ceramic support
RESISTOR symbol
Hydraulic analogy.
The greater the value of the resistance, the
smaller the current which will flow through it.
B3-01
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desired is obtained by acting on
the type of mixture and the
quantities. These resistors are
generally more temperature
stable and more precise than the
carbon type resistors.
The resistor body is generally
painted with yellow rings which
correspond to an international
identification code. The colour
code identifies the ohm value
and the manufacturing toler-
ance of the resistance, due to
the impossibility of obtaining
absolute precise ohm values an
effort is made to manufacture
within certain tolerance limits, a
colour code has been established
to indicate these limits.
The size of the resistors has a
direct relation to the amount
of power they can dissipate.
Standard power figures range
from 1/8 th of a watt to several
watts. When hi gher power
figures have to be absorbed it is
more common to find
wirewound or vitrified resistors.
Resistor colour code
In order to interpret the
international colour code, the
resistor should be placed so the
“gold” or “silver plated” band (which
indicates the tolerance) is located at
the right.The colour code bands are
read from left to right.
The first two bands designate
numerical values, while the third
band is a multiplier that tells how
many zeros to add to the ohmic
value.
The standard tolerance values
are: 20 %, 10 %, 5 %, 2 % and 1 %.
For tolerance values under 5 %
metallic foil resistors are used.
1st digit 2nd digit
Multiplier Tolerance
1 st Digit Brown (1)...1
2 st Digit Blak (0)...... 0
Multipl ier Red (2).. ... .. .. 00
1.000 Ω
RESISTOR COLOUR CODES
BLACK
BROWN
RED
ORANGE
YELLOW
GREEN
BLUE
VIOLET
GREY
WHITE
X1
X10
X100
X1.000
X10.000
X100.000
X1.000.000
-
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
B2-F2I N T E R E S T I N G F A C T S
Th e s i z e o f t h e r e s i s t o r s b e a r s a
d i re c t re l a t i on sh ip t o t h e amoun t o f
p owe r t h e y c a n d i s s i p a t e .
The d i a g ram shows t h e ou t l i n e o f
s ome re s i s t o r s , enab l i n g t h e i r powe r
va l u e t o b e de t e rm ined f rom t he i r
s i z e .
Wirewound
Ceramic resistor
TYPES OF RESISTORS
5
SILVER
GOLD
10 %
5 %
2 W
1 W
0.5 W
0.25 W
TOLERANCE
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Variable resistors and
potentiometers
A potent iometer is a
res istance on which a
s l id ing pointer d ivides the
res istance in two parts
whose sum is cons tant . The
res istance is made up of a
carbon f i lm or a res ist ive
wire coi l depending on its
va lue and power
speci f icat ions . Potent iometers
made from a f i lm of res istant
plast ic or conduct ive ceramic
a lso exist .
A needle moves a long the
res istance and makes contact
between the termina l which
corresponds to the base
of the needle and one of the
outputs . The movement of the
needle could be s imple or
mult i -rotat ion, the latter
of fers more precise
adjustment .
Applications of potentiometers
Potentiometers are basically
used as voltage dividers or
current reducers, a common
potentiometer application is in
the fuel gauge, in the light
intensity regulator of the dash
panel or integrated in the
headlight height adjustment
mechanism.
Exit+
-
PA S S I V E CO M P O N E N T S :VA R I A B L E RE S I S T O R S
“Variable resistors are those whose resistance
could vary under the influence of some physical phenomena
such as temperature, light or magnetism and they
can therefore be used as sensors”.
B3-05
LAYOUT OF APOTENTIOMETER
The resistance value betweenA and C is fixed
The resistance value betweenA and B or B and C is variable
Slidingpointer
POTENTIOMETER symbol
A C
B
Various types of potentiometers
Potentiometer for headlightreach adjustment
Miniature multi-rotation potentiometers
Partial rotary potentiometer
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Special resistors
As well as the fixed resistors
and potentiometers, certain
resistors are available whose
resistance varies under the
influence of some physical
phenomena.
These special characteristics are
available of in applications
where it is necessary to have
components capable of
detecting and measuring
temperature, voltage, pressure,
traction, etc. They have many
applications in the automobile
since they are among the
components none as sensors:
these are components capable
of transforming a physical
variation into an electrical
variation.
NTC resistors (Negative
Temperature Coefficient)
NTC resistors are capable of
reducing their resistance as
their temperature increases.
They are made from ferric
oxide semiconductors and
they could be designed in
diverse shapes: encapsulated
in the shape of a drop, tablet,
spherical, f lat, or other
shapes.
The resistance variat ion is
generally in the range between
-3 and -5 % per centigrade
degree and the nominal value
is usu ally taken at 25 °C . They
are commonly used for
measuring air temperature (in
air intake, air conditioning and
heating systems, etc.) .
7
NTC type resistor for temperature
sender and response curve.
Equivalent symbols forNTC resistors
ϑ
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PTC resistors (Positive
Temperature Coefficient)
PTC resistors increase their
resistance value as
temperature rises, althoughonly within a specific range
and outside this the change
could be zero or even
negative. A filament lamp is a
good example of a PTC
resistance, when cold, the
resistance is about a tenth of
its value when working and
hot.
A typical important use of the
property of PTC resistors is in
the area of diesel engine
preheating with plugs which
are self adjusting. Their
characteristic behaviour
consists in the increase of
their resistance as their
temperature increases, so that
when the plugs are cold their
resistance is very low, so a
very high current will f low
through them and therefore
their temperature will increase
very fast and quickly heat up
the pre-combustion chamber.
As the plugs heat up, the
current flow is reduced. This
property ensures rapid heating
and self adjustment of the
current consumption.
This resistance property of a
PTC, giving a rapid heating
with a self adjusting
consumption makes for an
excellent heating system which
is used to heat the lambda
sensor, the door lock barrels,
PTC type resistor for heater plug
and response curve.
Equivalent symbolsfor PTC resistors
ϑ
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the water jets for the window
wash to avoid freezing, etc.
LDR resistors (Light
Dependent Resistor)
LDR resistors are more
commonly know as
photoresistors, and are made
from a disk of semiconductive
material (generally sulphuric
cadmium) on which
semiconductor tracks are
printed.
Their resistance depends on
the amount of light shining on
them. As the light inc reases
their resi stance decreases . This
characteristic is used in
systems which switch on the
lights automatically, eg. when
the vehicle goes through dark
tunnels, and it is also used in
solar radiation detectors for
air conditioning systems.
VDR resistors (Voltage
Dependent Resistor)
The VDR resistors also known
as varistors, are resistors
whose value depends on the
voltage applied across their
ends.
They have a high electrical
resistance, which reduces under
the application of voltage. This
characteristic is due to the
materials used in their
manufacture, (silicon carbide
and titanium oxide). They can be
used to stabilise voltage, protect
a circuit or suppress the sparks
created by the brushes of small
V V
LDR VDR
Shape and response curve for LDR
and VDR resistance.
Photoresistor symbol (LDR)
Varistor symbol (VDR)
9
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Construction and
operation
A capacitor is a component which
has the ability to store electrical
charge, it is made basically from
two plates or armatures separated
by an insulator made from a
material called dielectric; when a
constant voltage is applied to the
armatures, an accumulation of
electrical charge takes place, so that
the plate which is connected to the
negative pole will be fill with
electrons, while at the other plate
(which is connected to the positive
side) an evacuation of electrons will
take place (holes).
If the source voltage decreases, the
capacitor will release its charge
until its electrical charge becomes
equal to the source again.
This ability to charge and discharge
is used to “filter” current. An
analogy can be drawn with that of a
“reservoir” which dampens and
regulates the current flowing
into it.
Capacitors also form part of the
oscillator and timing circuits and a
specific application can be found in
the ignition systems which are
based on a capacitor discharge to
the primary winding of the coil.
The material used in the
manufacture of a capacitor is very
important since it determines
factors such as the maximum
working voltage an above all the
capacity.
The symbol for the capacitor shows
LAYOUT OF A CAPACITOR
PA S S I V E CO M P O N E N T S :TH E CAPACITORS
“The capacitor is a component which possesses the ability
to store and release electrical charge and this characteristic converts it into
a very useful part of electrical circuits which require current to be “filtered” or
require the use of timing devices”.
CAPACITOR symbol
Armatures
Generic
Biased
Hydraulic analogy.
The capacitor acts like a reservoir
which dampens current
oscillations.
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11
two “plates” which divide the
circuit: the armatures. Depending
on the type of capacitor, it could be
biased, which makes it necessary to
take care as to the position of the
terminals when fitting, for example
the electrolytic type whose
capacitor symbol shows the polarity
of each terminal.
The capacitor reacts differently
when supplied with direct current
or alternating current.When direct
current is applied to the capacitor,
it charges to the same value as the
source but does not permit passage
of current. On the contrary, when
alternating current is applied, the
capacitor is charged and discharged
according to the current
fluctuations and it permits the
passage of current. If we refer to
the hydraulic analogy, the capacitor
could be compared to a reservoir
divided by an elastic membrane.The
water current will not flow when it
is continuous since the membrane
will stop it.The water is stored
with a specific pressure, being equal
to that in the circuit.
However if the water is moved by
impulses, the membrane will
transmit these pressure variations
to the opposite chamber thus
producing water circulation.
This characteristic in relation to
alternating current is used to filter
a continuous current superimposed
on an alternating one, allowing it to
pass and retaining the continuous
current; also another use is in
switching circuits which have
inductive charges (relays, coils,
etc.).
·Types of capacitors
These can be classified
according to the material used
in their manufacture and their
capacity:
·Ceramic and plastic, for
low capacitance.
·Polyester and tantalum,
for medium capacitance.
·Electrolytic, for high
capacitance.
Waterpressure
Elastic membrane
Hydraulic comparison of the reaction of the
capacitor to alternating current.
Polyester
Plastic
Electrolytic
Ceramic
Tantalum
TYPES OF CAPACITOR
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Applications of capacitors
·Filters, resonant circuits
To prevent parasitic noises in
car radio operation, capacitorsare used as current filters due
to their properties in relation
to ac and dc current.
Capacitors are fitted in
parallel with inductors (coils,
relays, etc.) or other sources
of parasitic noises (switches,
motors, etc.) and deviate to
earth any alternating current
peaks susceptible of creating
interferences.
When fitted at the outlet of
the rectif ier, as shown in the
diagram, the capacitor
“flattens” the voltage peaks
since it is charged during the
build up of the positive
waveform and discharged when
the wave form begins its
descent, thus filling the vacant
areas with the charge
accumulated by the capacitor.
This effect produces a filtered
current and a greater voltage
efficiency.
When an alternating signal is
needed for processing from a
direct current which has
pulsations (rev counter) a
series fitting is done so that
only the alternating part of
the signal is passed.
A capacitor fitted in series
with a coil (inductor),
constitutes a resonant circuit
which performs as a filter for
a specific frequency of
oscillation, and this method is
used for the reader unit of the
electronic immobi liser, since
the circuit is capable of
I N T E R E S T I N G F A C T S
Units of capacitance
The capacitance (C) of a capacitor is directly
proportional to the amount of electrons stored
in each plate (Q) and indirectly proportional to
the voltage applied to each one of the
plates (U).
This can be expressed by the formula:
C = Q/U
1 farad (C) = 1 coulomb (Q) / 1 volt (V)
C = Capacitance of the capacitor in farads (F)
Q = Amount of electrical charge in coulombs (C)
U = Potential difference between the plates in
volts (V)
The unit of capacitance called the farad is the
relation between the amount of electrical
charge (Q) in amperes per second which can
be stored by a capacitor and the voltage
between its plates.
The unit of electrical charge (Q) is the coulomb
and is defined as the amount of electrons
transferred by one ampere (A) in time period of
one second (s) between two points in a circuit.
This means that one coulomb is the same as
one ampere per second (C = As). In reality a
farad is a very large value, so that in practice
only fractional values of farads are used:
MICROFARAD mF = 0,000001 F
N AN OFA RAD nF = 0 ,0 01 mF
PICOFARAD pF = 0 ,001 nF
Diagram of a half wave rectifier with
a filter capacitor.
Capacitoreffect
Non rectifiedcurrent
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“recognising” the signal
emitted by the key.
Timing devices
A capacitor is used as a timing
device in combination with aresistance fitted in series. The
capacitor charges or discharges
through the resistance in a
specific period of time. This
method is used to control
illumination period of the
interior light or as a part of the
reserve operating module for
the Airbag Control Unit.
I N T E R E S T I N G F A C T S
Time constants RC
Despite the fact that a capacitor charges in
a NON LINEAR fashion, since at the
beginning it charges very quickly and then
more and more slowly, there is however a
section of the curve (charging and
discharging) which is practically linear and
this is the section which is used to calculate
the time constant (T).This constant is the
time the capacitor takes to charge to 63 %
of the supply voltage value.The discharge is
calculated in the same fashion, and the time
(T) for the RC constant is obtained when the
capacitor has discharged to 37 % of the
source voltage value.
13
12 V (100 %)
7,56 V
V
V
T t
12 V
R
R
12 V (100 %)
4,44 V
T t
12 V
R
R
CHARGING CURVE
DISCHARGING CURVE
The capacitor constantly charges and
discharges through a resistance.
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Semiconductors
In electronic technology, we
distinguish between two types of
materials, those which conduct
electricity, called conductors and
those which resist conduction,
called non conductors or
insulators . However between the
conductive and insulating materials,
there is the third group called
semiconductors .These
components originate from
materials, which in their natural
and pure state are insulators, but
they can become conductors, due
to the introduction (doping) of
impurities from other different
substances.
In insulating materials the electrons
are strongly attached to the atoms
forming a crystalline network,
making conduction impossible,
while in conductors the electrons
can be easily pull away and
conduction takes place due to the
free movement of these electrons.
Doping
The nature of semiconductors
materials, such as silicon or
germanium, is such that in their
pure state they are insulating
crystals, however if their atomic
structure is contaminated with
arsenic, gallium or indium
they are transformed into crystals
which facilitate the conduction of
negative or positive charges.The
joining of these two crystal
varieties creates a component
whose current conduction
properties are completely
different to those of the crystals
in their pure state.
·Creation of N and P type
crystals
The manufacture of the crystals is
achieved by doping, which consists
in the addition of specific
quantities of other elements to
the material in its pure state.
For example silicon (four
electrons) can be doped with
antimonium or indium, the atoms
of the doping material will mix
with those of the semiconductor;
these could be one which has an
excess electron (antimonium with
five electrons) in its external shell,
in which case each atom of the
doping material provides an
electron which is not connected
to the crystalline structure
AC T I V E CO M P O N E N T S
“Active components are those which form part of
electrical circuits and systems providing the possibility to
switch or regulate the current.
These components cover the group known as semiconductors”.
Sketch of the internal structure of
pure silicon.
All the atoms form a crystalline network
which share electrons with the adjoining
atoms.
SILICON ATOMWith four electrons in its
external shell shared with theadjoining
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Free electron
Indium atom
Hole
Antimonium atom
N type crystalCrystalline structure of silicon doped with anantimonium atom which has five electrons.
One electron remains free.
P type crystalCrystalline structure of silicon doped with an
indium atom which has three electrons.One hole remains free.
and is there for “free” to act
as a charge carrier; the crystal
thus obtained is known as
N type.
Alternatively, the silicon
semiconductor can be doped with
a material which has three
electrons in its external shell
(indium), so that where this doping
material is placed, an electron will
be lacking and a connection will be
made with the nearest silicon
electron.This lack of an electron is
known as a hole, although this unit
does not exist as such and it only
refers to a missing electron, it can
be considered as a charge carrier.
The silicon atom now has a
vacancy or hole which can “travel”
as an electron, although the
mobility of the holes is based on
the change in the position of the
electrons connected to them and
not to their real physical
movement.
The material which has been
doped in this way is known as a
P type crystal since it is capable
of moving “holes”, as opposed to
the electron which could be
considered as a positive charge
carrier. 15
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The PN junction: the
diode
The joining of two P and N type
crystals forms a semiconductor
diode. Current will pass in one
direction only, and the diode will
offer high resistance to passage in
the other direction.
·P o l a r i s a t i o n o f a
s e m i c o n d u c t i v e d i o d e
When a reverse polarity is applied
to the junction (reverse bias), the
electrons are pulled towards the
positive pole and move away from
the zone where the holes are
located.A barrier is thus formed
which makes the flow of electrons
difficult.
When a direct voltage is applied
to the junction (forward bias), the
electrons flow in the opposite
direction and when they reach the
centre of the junction they are
able to jump to the holes of the
adjoining element, and flow
towards the positive pole.The
insulating barrier is thus removed
and electrons can flow freely.To
generate current flow, a minimum
voltage capable of overcoming the
inherent potential barrier needs
to be applied.This voltage
depends on the nature of the
semiconductor material, in the
case of silicon which is the most
commonly used material, the
voltage required is 0.7 volts and
for diodes made from germanium,
the minimum voltage is 0.3.
Forward and reverse biasing of a diode.
AC T I V E CO M P O N E N T S :TH E D I O D E
“The joining of two P and N type crystals creates the first of the active components:
the diode, whose operation is similar to that of an electrical valve”.
Anode Cathode
DIODE symbol
REVERSEbiased
(no conduction)
Anode Cathode
FORWARDbiased
(conducts)
Ring which indicatesthe cathode
DIODES
Diode for high power
Diode for low power
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P type crystal N type crystal
Flow of electrons
Conventional current(holes)
Anode Cathode
Hydraulic comparison
The working cycle of the diode
shows how the current varies
according to the biasing applied.
The horizontal axis represents the
voltage value applied and the
vertical axis indicates the current
flowing. It can be seen that when
forward biased (a), current will
flow, while when reverse biased (b),
the current flow is so small
that it is practically negligible.
When the reverse voltage is
increased (c), we enter the
breakdown area where the diode
could degenerate.
Diode applications
·Application as a rectifier
The characteristic of the diode
which enables it to operate as a
one way valve, makes it ideally
suited as an alternating current
rectifier.
The number of diodes used
depends on the number of
phases and the alterations: on a
single phase alternator, four
diodes are required (two for
each phase). On a three phase
alternator, six diodes are
needed.
Working cycle of a diode.
Internal structure of diode made from
two crystals, N and P type and the
hydraulic analogy.
bc
I
V
a
Diagram of a rectifier bridge with four diodes
E
E
Diagram of a rectifier bridge with six diodes for a three phase alternator
17
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Fitting of diodes in the
instrument panel
Diodes are normal ly used in
the instrument panel to
prevent the return currentform l ight ing the charge
warning l ight in the
instrument panel .
The diagram shows the
f it t ing of a d iode to prevent
the reverse f low of current
in an a lternator excitat ion
circuit .
When the key is switched on
with the eng ine s topped, the
required current for
excitat ion f lows through the
res istors and the warning
l ight .
When the car has been
started and current
generat ion has c ommenced, a
voltage is generated in
termina l D+ (with
a current f lowing in the
oppos ite d irect ion) and the
charge warning l ight goes
out. The diode prevents
reverse f low of current and
consequent backfeeding of
ignit ion l ine 15.
·Voltage peak protection
When a d iode is f i t ted in the
30
31
D+
D
G
K2
R2
R1
15
G: Alternator.
D+: Energising terminal.
K2: Charge warning light.
D: Diode.
R1 and R2: Resistors.
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reverse d irect ion in an
induct ive supply c ircuit , ( for
example , a re lay) , i t acts as a
sa fety va lve which shorts to
earth any voltage peaks
caused by the autoinduct ion
ef fect which could be
dangerous for the e lectronic
circuits .
The coil in a relay, when fed
with a current , creates a
magnet ic f ie ld needed to pul l
the armature and close the
power switch. When the
supply is removed, the
magnet ic f ie ld d isappears
s lowly, and this s low
variat ion in the f lux wi l l
autoinduce a high voltage in
the coi l with a polarity
opposed to that of the
supply. This creates s erious
danger for the vehicle
e lectrica l insta l lat ion. The
diode which was reverse
biased wi l l now become
forward biased, short-
circuit ing the voltage peak
which occurs between the
ends of the coi l , thus
diss ipat ing a l l the energy at
this point .
19
Relay with protection diode.
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Zener diode
The Zener d iode a lso known
as the regulat ing d iode is made
in the same fashion as a
normal d iode except for the
fact that the doping materia l
introduced into its interna l
structure (PN junct ion) makes
it work in the “breakdown”
area without degenerat ing .
This part icularity means that
in the reverse d irect ion it
becomes a one way e lectrica l
va lve which “opens” to
regulate and mainta in a
constant voltage .
The voltage at which the d iode
“opens” is known as the
Zener voltage and this is
dependant on the
manufacturing characterist ics
of the component .
This characterist ic converts
the Zener d iode into a very
useful component in circuits
where the voltage has to be
mainta ined at a f ixed leve l (as
a regulator for an a lternator)
or to suppress voltage peaks
created by coi ls or inductances
which could be dangerous for
an e lectrica l insta l lat ion.
The working characterist ic
curve of a zener d iode shows
how it works in the
breakdown area (c) when
reverse biased, when the zener
voltage is reached the diode
becomes conduct ive and the
current f lows suddenly. When
forward biased, the zener
diode works l ike a normal
diode.
LED Diode
The l ight emitt ing d iode or in
abbreviated form LED, is a
luminous d iode made from
arsenium ga l l ium encapsulated
in plast ic . The operat ion of the
ACTIVE COMPONENTS:ZENER D IODES, LED AND PHOTODIODES
SHAPE OF ZENER DIODE
B3-27
ZENER DIODE, HYDRAULIC COMPARISON
The valve calibrated at a pressure of 10 kg will only open when this pressure is exceeded
Constantpressure
Calibrationpressure
Inletpressure
Inletpressure
1010 1012 2
10
bc
IOperatingarea
V
a
“Some diodes have special characteristics which make
them useful for various tasks such as, voltage regulation and light emission
in the same way as a warning light or they can be used to detect
a certain level of light intensity”.
Equivalent symbols forZENER DIODE
Anode
Ring whichindicates the cathode
Cathode
Working cycle of zener diode.
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Anode Cathode
Symbol for LED DIODE
21
LED is based on the principle
that when the diode is
forward biased, the movement
of the e lectrons in the PN
junct ion g ives of f l ight energy
in the form of photons . I f i t is
subjected to more than
5 volts , i t wi l l degenerate .
The colour of the LED
depends on the materia l used
to make the PN junct ion. I t
can a lso be dua l coloured
depending on the bias
received.
The appl icat ion of l ight
emitt ing d iodes is mainly in
the area of i l luminated
indicators and di splays . They
could be f i t ted as segments or
as part of a matrix of points ,
in which case they are used to
reproduce graphica l symbols
or ana log indicat ions .
A specia l type of d iode known
as intermittent , is a LED with
a minute e lectronic circuit
ins ide the capsule which
f lashes with a frequency of
about 3 Hz.
There are a lso d iodes which
emit l ight in the invis ib le
spectrum, known as infrared,
which are used for remote
control systems.
Photodiode
This has a s imi lar des ign to
that of a normal d iode except
for the fact that i ts coat ing
is transparent . I t is usua l ly
reverse biased and is normal ly
used in circuits des igned to
measure l ight intensity, or in
those which have to respond
to a set level of l ight intensity.
Certa in photodiodes which are
sens it ive to infrared radiat ion
also exist and are used for
anti-theft control and the
operat ion of remote
control led centra l lock ing
systems.
Each one of the seven graphical
“segments” of the number is
made from a LED.The diagram
shows their layout.
Semiconductor
Diffusing lens
TerminalsAnode
Cathode
LED DIODE
LEDindicator
LED supplyterminals
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Transistor
characteristics
A transistor is a semiconductor
component which is made of P and N
type materials, making a junction of
three semiconductor elements: these
could be of the PNP or NPN type,
depending on the layout of the
crystals. In practice the difference lies
in the polarity required by each
transistor to enable it to operate
correctly. Transistors have three
electrodes or connectors: the
Collector (C), the Base (B) and
the Emitter (E) and to enable
current to flow between the
collector and the emitter, the base
must be biased by means of a control
current. The voltage which needs to
be applied to the base (in relation to
the Emitter) to enable the transistor
to conduct current is about 0.7 volts
in the case of silicon transistors.
Operation
When the emitter base junction is
forward biased (as in a diode), the
barrier which separates them is
broken down and the flow of
electrons is permitted towards the
base. When the barrier is broken
down, the electrons can now also
move towards the collector.
The conventional current flow
(holes) takes place in the opposite
direction.
Using the hydraulic analogy, we can
say that a transistor conducts
when it receives a small current at
the base which opens the flap. The
regulation of the flow could vary
from zero to the maximum,
depending on the consumption of
the component being supplied by
the transis tor.
The current which flows through
the collector (Ic) could be very
AC T I V E CO M P O N E N T S :TH E TR ANS I S T O R
“The transistor was invented in 1948, it is a extremely
important electronic component since it acts as a unit which enables
small current values to be amplified and it can also work as an
electronic switch without metallic contacts”.
The transistor.
The union of three elements makes up the
internal structure of the transistor.
NPN transistors symbol
PNP transistors symbol
C
CE
B
E
B
TRANSISTORS
C B E
TRANSISTOR OPERATION
Flow of holes
Flow of electrons
Hydrauliccomparison
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large compared to that required
by the base, making the operation
of the transistor similar to that of
a relay: the relay terminals (30 and
87) could be compared to the
emitter and collector respectively,
while the coil feed terminals (86
and 85) could be compared to the
transistor base.
The main difference between the
operation of a relay and a
transistor lies in the ability of the
transistor to commute very high
current values at great speed
without creating voltage peaks and
only requiring very low base
current.
Transistors in the automobile
electronics industry are generally
used in switching circuits, being
used as rapid operating switches.
The Transistor changes its
electrical state, passing from being
a conductor at the Emitter
Collector junction to that of an
insulator without any transition
phase. Under these conditions, it is
said that the transistor is
operating in the saturation mode,
meaning that the Collector Emitter
junction has minimum resistance
and passes maximum current.
PNP and NPN
transistors
Depending on the internal layout
of the elements, transistors could
be PNP or NPN type. The
electrical characteristics are
practically similar (although the
NPN transistor switches a little
faster and is slightly cheaper to
make).The main difference is in the
bias voltage of the base. The PNP
works with negative base voltage,
while the NPN needs positive,
they are therefore symmetric or
complimentary, and operate in the
same way but with opposite
voltages.
23
Transistors could be PNP or NPN depending
on the crystal layout.
Ic
30 87
86 85
Comparison between a transistor and a relay.
Conventional current
Crystal junctions for transistor construction
PP N NN P
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Applications as voltage
regulators and
switches
Some transistors are made to
operate as voltage regulators
and others are destined as
switches. Switching requires
transistors which can operate
very fast and transmit very high
power, while voltage regulating
transistors must have a very
high gain factor. In the first
case, the transistor operates as
an open or closed switch, while
in the second case it operates
as a valve which regulates the
flow of current in a circuit
between a minimum and
maximum value.
The transistor is used as an
electronic switch and can be
found in the secondary power
circuits of the ignition and
injection, regulating circuits and
audio systems, etc.
Trigger circuits (Schmidt
trigger)
Here the transistors are fitted
in such a fashion that the out-
put signal does not changeuntil the input signal has
reached a certain value. Its
applications are numerous,
since a trigger circuit can be
used to shape pulses (make
them rectangular) or detect
slow voltage variations, such
as those provided by a tem-
perature sensor, in order to
perform an action when a set
value is reached.
The example in the diagram
shows how the lamp (B) lights
when the signal at the point
(A) reaches a set voltage.
This set up could be used to
convert sinusoidal waveforms
into rectangular shaped waves.
At the input to the first tran-
sistor a sinusoidal signal is
applied (slow increase and
decrease), while the on and off
signal of the lamp is made in
the form of instantaneous
pulses.
·Electronic regulat ion
In an al ternator regulator, a
transistor operates as a switch,
to enable the current to flow
through the excitation winding
in order to magnetise the rotor
I N T E R E S T I N G F A C T S
One o f t h e mos t impor t an t
cha ra c t e r i s t i c s o f t h e t ran s i s t o r
compared to a re lay i s i t s ab i l i t y to
“amp l i f y ” a sma l l c u r ren t t o a ve r y
h i gh va l u e .
Th i s ampl i f i ca t ion i s ach ieved th rough
the re la t ion be tween the cu rren t a t
t h e ba se ( I b ) wh i c h i s v e r y sma l l a nd
t ha t o f t h e c o l l e c t o r ( I c ) wh i c h c ou l d
b e ve r y l a rge . Fo r a s e t c o l l e c t o r
c u r ren t , a ve r y m inu t e ba se c u r ren t
i s r equ i red and t h i s r e l a t i on sh ip i s
ca l led the forward curren t ga in , a l so
known by the Greek symbol ß , “be ta” .
Th i s ga i n f a c t o r i s a f i gu re wh i c h i s
g i ven by the t rans i s tor manufac tu rer .
F o r e xamp le a c ommon t ran s i s t o r
w i th a be ta fac tor of 100 , means
t ha t i f t h e ba se i s s upp l i e d w i t h
1 mi l l iAmp, 100 mi l l iAmps can f low
th rough the co l lec tor .
Trigger circuit.
The lamp (B) lights when the
signal at the point (A) reaches
a set voltage level.
A
Sinusoidal waveform at A
Rectangular
wave format B
B
TR ANS I S T O R APPLI CAT I O NS
“The field of application of transistors is very vast,
since they could be used as electronic switches or current regulators.
They are an essential part of the power circuits
of electronic control units”.
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and enable current to be
generated in the stator.
· Power regulation circuits
The transistors destined for
power regulation have an
advantage over
potentiometers. The example
shown in the diagram is a
simplif ied sketch of the
adjustment system for the fan
speed on the SEAT Alhambra.
The electric motors for the
fans V2 and V80 are su pplied
directly with positive through
the relay J323, and receive
negative from the power
transistors J126 and J391,
which are fitted in series.
These transistors operate as
current regulators, providing
more or less current to the
motors. The transi stors are
governed by the control unit,
supplying the base of each
transistor according to the
program which has been
selected.
·Transistorised ignition
circuits
In a transistorised ignition
circuit, the transistor takes on
the function of an electronic
switch since it is used to pass
the high current for the coil
primary winding, the control
signal could be generated by a
magnetic impulse or Hall
sender.
I N T E R E S T I N G F A C T S
The Darlington pair
This arrangement means that the transistors
are mounted in such a way that the two
collectors are connected to a common point
and the emitter of (T1) is connected to the
base of (T2).This arrangement known as the
Darlington pair is characterised by its high
forward gain factor (ß), since the total “beta”
(ß) or total gain factor is the multiplication of
the individual “beta” values, in other words:
ß total = ß1 x ß2.
This assembly is generally contained in one
capsule as if it was one single transistor an it
is used in power stages and switching circuits.
This arrangement is used in the ignition coil
secondary winding amplification.
The diode (D) fitted in parallel between the
emitter and collector and mounted in the
reverse direction is designed to protect the
transistor from voltage spikes which normally
occur in inductive circuits and which are of
opposite voltage to that applied in the circuit.
25
TRANSISTOR APPLICATION TO REGULATEFAN SPEED
30
J323: Control relay.
V2 and V80: Fans.
J126 and J391: Power transistors.
Control unit
J323
V2 V80J126 J391
D
T2
T1
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The thyristor
The thyristor, also known as a
controlled diode or SCR (Silicon
Controlled Rectifier) is a
semiconductor made of four
layers of silicon with alternating
P and N polarities. It could be
considered as the combination of
two independent transistors, one
PNP and one NPN type. It has
three contacts, the anode (A), the
cathode (K) and the gate (G) or
controlling electrode.
It operates like a controlled
diode, and starts to conduct
when its controlling electrode
(G) receives a positive impulse,
this impulse could be of very
short duration and provokes the
thyristor to start conducting. It
will continue to conduct until the
input current at the anode (A) is
cut off or the voltage drops to
zero.
·CDI ignition
An application of thyristors can
be found in the electronic
ignition of automobiles and
motorbikes operating on the
(CDI) capacitor discharge
principle. The sketch in the
diagram shows an ignition
system using condenser
discharge (CDI).The capacitor
is charged with 400 volts.
When the thyristor receives a
trigger impulse from the
control unit, it immediately
conducts, thus discharging
400 volts from the condenser
onto the primary winding of
the coil, and to the secondary
winding by induction, thus
creating high voltage.
AC T I V E CO M P O N E N T S :THE THYRISTOR, PHOTOTRANSISTOR,TRIAC AND DIAC
B3-39
LAYOUT OF A THYRISTOR
Crystal junction
Internal circuit
Anode(A)
Anode(A)
P PN N
Cathode(K)
Cathode(K)
400 Vsupply
Plug
Trigger
P
S
C
Gate(G)
Gate(G)
CDI ignition system sketch.
The condenser discharge onto the primary
winding (P) using a thyristor creates a high
voltage in the secondary winding (S).
“Although thyristors, phototransistors, triacs and diacs are little known
components; however a knowledge of their operation will greatly help to
understand the operation of certain electronic devices”.
THYRISTOR symbol
Cathode (K)
Anode(A) Gate
(G)
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TRIAC symbol
Phototransistors
These components have a
structure similar to that of a
normal transistor, the
phototransistor has a window in
its capsule (lens shape) which
concentrates light on the junction
of the transistor elements, so
that when light shines on the
phototransistor, a base current is
created. This current is amplified
as in the normal operation of a
transistor and therefore the
current at the collector is
increased.
Diacs
The diac (Diode Alternating
Current) is a bi-directional
component which is generally used
in combination with a triac.
When the voltage applied to its
ends reaches a specific value
(about 30 volts) the component is
primed and its resistance changes
form high to low, and it then holds
a voltage value of about 24 volts.
Triacs and diacs are very useful
components for building control
circuits for alternating current.
Triacs
A triac (Triode Alternating
Current) operates in the same
fashion as a thyristor. It consists
of a diode controlled in both
directions and it is used in full
wave rectification (for alternating
current circuits).
It operates as a bi-directional
diode (two thyristors fitted in
opposite directions) which needs
a gate current impulse to start
conducting. The current
conducting time of the positive
and negative half of the wave can
be controlled, making the triac a
very efficient component for the
control of devices supplied with
alternating current.
The following illustration shows a
light intensity control for a bulb.
The combination of a
potentiometer, a diac and a
condenser enables the triggering
of the triac to be delayed and
regulates the intensity of the
bulb (E) since according to the
position of the potentiometer the
bulb receives a partial alternating
current wave and thus a variation
in the voltage.
PHOTOTRANSISTORS
Collector
Emitter
Housing
Lens
C
E
C.A Triac
Diac
Potentiometer
Current
through
triac
FULL WAVE CONTROL CIRCUIT
A1 A2
Gate
DIAC symbol
PHOTOTRANSISTOR symbol
C E
27
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Types of integrated
circuits
Integrated circuits (IC) were
designed to carry out several
specific functions, which means
that a great variety of circuits
exists for many diverse
purposes.
Present IC can be divided into
two groups, according to the
basic use for which they have
been designed: either for analog
or digital circuits. Analog
circuits are used where
electricity varies in a linear
fashion (amplif ier circuits,
timing devices, etc.); on the
contrary, digital circuits work
on the bases of definite pulses,
being the origin of
microprocessors and
memories.
The vo l tage s tab i l i sers make
up one o f a ser ies o f ( IC)
used in the automobi le and
these are f i t ted to the
ins trument pane l to supp ly
the indicator gauges . A
constant f ixed vo l tage i s thus
ensured, irrespect ive of
ba t tery vo l tage , which cou ld
vary s l i ght ly accord ing to
eng ine rpm.
Hybrid Circuit
The des ign and construct ion
of power c ircu i t s (e .g .
i gn i t ion co i l s ) a re made us ing
the heavy layer hybrid circuit
technology. Severa l layers of
semiconductor mater ia l i s
p laced on a ceramic base ,
forming d i f f erent e lectron ic
components such as :
res i s tors , d iodes , t rans i s tors
and integra ted c ircu i t s ,
accord ing to the connect ions
which are made . Other
components such as
Dar l ing ton pa irs can a l so be
welded onto the
semiconductor mater ia l .
Th is makes i t poss ib le to
bu i ld a hybr id c i rcu i t
which inc ludes both the
technology o f the integra ted
c ircu i t together with the
vo luminous h igh power
components .
INTEGRATED C I R C U I T S
“Ten years after the discovery of the transistor in 1958, Jack Kilby from Texas
Instruments built the first integrated circuit, which included on one single silicon
chip components such as: transistors, diodes, resistors and capacitors.
All these components were connected in such a way that they made up a circuit
specifically designed for a concrete application”.
INTEGRATED CIRCUITS
HYBRID CIRCUIT
Stabiliser
12 V
15
31
J6
G1
G3
10 V
INSTRUMENT PANEL CIRCUIT
J6: Stabiliser.G1: Temperature indicator.G3: Fuel indicator.
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Printed Circuit
Electronic circuits made from
discrete components
(transistors, resistors) or
integrated circuits are generally
mounted on a printed
circuit.
A printed circuit consists of a
flat insulating plastic film
(usually fibreglass) on which
copper conduction tracks are
printed: the tracks join the
individual components.
For very complex circuits,
several layers of film are used,
which join components in
three dimensions, thus reducing
the size of the circuit even
more.
The manufacture of an
integrated circuit is initiated by
drawing the circuit tracks
between the different
components on film or
transparent p lastic foil. This
transparency is then used as a
photolith to transfer the
drawing to the copper plate
(the plate has a copper coating
which covers the entire surface)
which is also treated with a
ultraviolet light sensitive
material (similar to a
photographic film). Thetransparent film (the negative)
with the circuit tracks is placed
on top of the sensitive copper
plate and the track is then
transferred to the copper.
Finally the plate is submitted to
an acid treatment which attacks
and dissolves all the areas not
exposed to li ght, thus
transferring the tracks onto the
plate.
The components to be placed
on the plate can be welded
manually or automatically with a
layer of molten solder.
Printed circuits provide a base
for the fitting of
electronic components.
29
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V
+12 V
75 %
S E L F - C H E C K E X E R C I S E S
1 . Determine the value and
tolerance of thefollowing resistors:
A ................. B .................
C ................. D .................
2. High power resistors are
made from:
A. Metallic foil.B. Wirewound.
C. Carbon.
3. Determine the voltage
supplied by the
potentiometer on the
diagram if the pointer has
reached 75 % of its travel.
R .................................................
4. The voltage curve of the
Digifant throttle
potentiometer. Determine
the voltage supplied when
the throttle is open to
45 degrees.
R .................................................
The following questions serve as a self check to enable you todetermine your understanding of the subject matter.
A
B
C
D
0o 10o0
1.0
2.0
3.0
4.0
5.0
20o 30o 40o 50o 60o 70o 80o 90o
Potentiometer output voltage
o Throttleopenning
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31
5. When an NTC type
resistor is cooled it value
will:
A. Increase.B. Decrease.C. Remain static.
6. The adjoining graph shows a
coolant temperature
transmitter.With a
resistance of 350 ohms,
what is the corresponding
engine temperature?
A. Between 18 and 20º.B. Between 80 and 90º.C. Between 75 and 85º.
7. VDR resistors are used for:
A . To suppress int erferences
caused by sparks.B. To detect voltage.C. To protect against polar ity
changes.
8. A high value capacitor fitted
after a rectifier diode helps
to:
A. Convert alternating current
to direct current.B. Provide a more constant
direct current.C. Prevent passage of
alternating current.
9. Electron current flows
through the diode as
shown on the sketch:
A.
B.
C.
A
B
C
100
0 oC
ΩΩ
10 20 30 40 50 60 70 80 90100
200
300
400500
600
700
800
900
1000
1000
2000
3000
4000
5000
6000
7000
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10. The voltage drop in a
forward biased diode is:
A. 0,7 A.B. 0,7 mV.C. 700 mV.
11. To enable a PNP typetransistor to conduct, the
base has to be:
A. Reverse biased.B. Forward biased.C. Supplied with direct
current.
12. Whe n wi l l the bu lb i n
the ad jo in ing c i r cu i t
be l i t ?
A. With the switch in the
pos it ion A.B. With the switch in the
pos i t ion B .C . I t w i l l b e
p e r m a n e n t l y l i t .
A
B
V
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33
ANSWERS:
1:A.(1kΩ10 %) B.(10 kΩ5 %) C.(470 kΩ5 %) D.(2,2 MΩ5 %)
2:B.3:(75/100) x 12 = 9 V.4:2,5 V.5:A.6:C.7:A.8:B.9:C.
10:C.11:A.12:B.13:C.14:B.15:A.
13. If the first transistor
has a beta value of 100
and the second has a
beta value of 10, when
a current of 1 milliAmp
is applied to the baseof the first transistor,
what current will flow
through the bulb?
A. 10.000 mA.B. 100 mA.C. 1 A.
14 . The following symbolcorresponds to a:
A. Phototransistor.B. Thyristor.C. Triac.
15. On a control unit with a
microprocessor, we can
deduct that the majority
of the circuits will
operate on the principle
of :
A. Digital.B. Analog.C. Both.
1 mA
100
10
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