3 CONCEPTOS DE ELECTRONICA

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ELECTRONICS

BASIC

OF3 COMPONENTS

POSTVENTAFORMACION

Service

BASIC SELF-STUDY MANUALS



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



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.



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



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



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



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



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



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



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.



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



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



“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.


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.



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



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



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



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



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.



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.



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.



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



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



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



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


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”.



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.


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



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)



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



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.



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



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



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



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



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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