week 4 chapter 3-electronic devices and transducers (2)

8/13/2019 Week 4 Chapter 3-Electronic Devices and Transducers (2)

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CGE535

Munawar Zaman Shahru

Faculty of Chemical Enginee

Universiti Teknologi MARA, Shah A

munawar_zaman@salam.uitm.edu

Tel: 03-5544 8019; 019-249

ELECTRICAL ANDINSTRUMENTATION TECHNOLOGY

Week 4

Chapter 3: Electronic Devices andTransducers

Describe the concept of semiconductors and its application

Explain the principle of diode, bipolar and field effecttransistors, thyristors and triacs operation and identify theifunction in various applications.

Describe Transducer application in electric circuit

Lesson Outcome

At the end of class, students should be able to:

TOPIC 1: Semiconductors

Semiconductors

What is Semiconductor?

Conductivity

Glass:10-16 and 10-13 S/cm Copper:0.59 x 106 S/cm Silicon10-8 x 10-1

Semiconductors

Definition:

Semiconductors are materials whose electrical properties between Conductors and Insulators.

Semiconductor is a substance, usually a solid chemical element

compound that can conduct electricity.

Semiconductors are materials that essentially can be conditionedact as good conductors, or good insulators, or any thing in betwe

Semiconductor is a material with electrical conductivity due electron flow intermediate in magnitude between that ofconductor and an insulator.

Why Semiconductors?

If you use conductors instead, you will have no control over voltage/electrical properties of your power source. We use semiconductolimit the properties of your power source to the desired output power. It’sused for logical circuits on your computer.

The main reason semiconductor materials are so useful is that the behavioa semiconductor can be easily manipulated by the addition of impurknown as doping.

Semiconductor conductivity can be controlled by introduction of an electrmagnetic field, by exposure to light or heat, or by mechanical deformation

doped mono-crystalline grid; thus, semiconductors can make excesensors.

Semiconductors in our Daily Lif

Examples of Semiconductors

Diodes

Transistor

Thyristors

Semiconductors

Common elements such as carbsilicon, and germanium semiconductors.

Silicon is the best and most wiused semiconductor.

Semiconductors

The main characteristic of asemiconductor element is that itfour electrons in its outer or valeorbit.

Semiconductors

The unique capability ofsemiconductor atoms is theirability to link together to form aphysical structure called a crystal

lattice. The atoms link together with one

another sharing their outerelectrons.

These links are called covalent

bonds.

Doping

A pure silicon crystal is nearly an insulator - very lielectricity will flow through it

To make the semiconductor conduct electricity, ot

atoms called impurities must be added. “Impurities” are different elements. This process is called doping. Intrinsic – based on temperature increment (no doping)

Extrinsic – based on doping with impurities.

Doping

An impurity, or element likearsenic, has 5 valenceelectrons.

Adding arsenic (doping) will

allow four of the arsenicvalence electrons to bondwith the neighboring siliconatoms.

The one electron left over for

each arsenic atom becomesavailable to conduct currentflow.

Doping: Different Approach

You can also dope a semiconductormaterial with an atom such as boronthat has only 3 valence electrons.

The 3 electrons in the outer orbit doform covalent bonds with itsneighboring semiconductor atoms

as before. But one electron ismissing from the bond. This place where a fourth electron

should be is referred to as a hole. The hole assumes a positive charge

so it can attract electrons from someother source.

Holes become a type of currentcarrier like the electron to supportcurrent flow.

Doping Effect

If you use lots of arsenic atoms for doping, there will belots of extra electrons so the resistance of the materialwill be low and current will flow freely.

If you use only a few boron atoms, there will be fewerfree electrons so the resistance will be high and lesscurrent will flow.

By controlling the doping amount, virtually any

resistance can be achieved.

Types of Semiconductor

The silicon doped with extra electrons is called an “N type” semiconduct

“N” is for negative, which is the charge of an electron.

In N-type doping, phosphorus or arsenic is added to the silicon in s

quantities. Phosphorus and arsenic each have five outer electrons, so they're ou

place when they get into the silicon lattice. The fifth electron has nothinbond to, so it's free to move around.

It takes only a very small quantity of the impurity to create enough electrons to allow an electric current to flow through the silicon.

N-type silicon is a good conductor. Electrons have a negative charge, hthe name N-type.

N:Current Flow

The DC voltage source has apositive terminal that attracts thefree electrons in thesemiconductor and pulls themaway from their atoms leaving the

atoms charged positively. Electrons from the negativeterminal of the supply enter thesemiconductor material and areattracted by the positive charge ofthe atoms missing one of theirelectrons.

Current (electrons) flows from thepositive terminal to the negativeterminal.

Silicon doped with material missing electrons that produce locations calledholes is called “P type” semiconductor.

“P” is for positive, which is the charge of a hole.

In P-type doping, boron or gallium is the dopant. Boron and gallium each honly three outer electrons.

When mixed into the silicon lattice, they form "holes" in the lattice where asilicon electron has nothing to bond to.

The absence of an electron creates the effect of a positive charge, hence tname P-type. Holes can conduct current.

A hole happily accepts an electron from a neighbor, moving the hole over aspace. P-type silicon is a good conductor.

P:Current Flow

Electrons from the negative supplyterminal are attracted to the positiveholes and fill them.

The positive terminal of the supplypulls the electrons from the holes

leaving the holes to attract moreelectrons. Current (electrons) flows from the

negative terminal to the positiveterminal.

Inside the semiconductor currentflow is actually by the movement of

the holes from positive to negative.

END OF TOPIC 1

23Video 1

TOPIC 2: Diodes

Diodes

The diode is the simplest and most fundamental nonlinecircuit element.

Just like resistor, it has two terminals.

Unlike resistor, it has a nonlinear current-voltagecharacteristics.

Its use in rectifiers is the most common application.

Diodes

The most important

region, which is callejunction, is the bounbetween n-type andtype semiconductor.

Diodes

Even though N-type silicon by itself is aconductor, and P-type silicon by itself is also aconductor, the combination shown in thediagram does not conduct any electricity

The negative electrons in the N-type silicon getattracted to the positive terminal of the battery.The positive holes in the P-type silicon getattracted to the negative terminal of the battery

No current flows across the junction becausethe holes and the electrons are each moving inthe wrong direction

Diodes

If the battery is flip around, the diode conducts electricity jusfine. The free electrons in the N-type silicon are repelled bthe negative terminal of the battery

The holes in the P-type silicon are repelled by the positivterminal. At the junction between the N-type and P-typsilicon, holes and free electrons meet

The electrons fill the holes. Those holes and free electroncease to exist, and new holes and electrons spring up to taktheir place. The effect is that current flows through th

junction

Diodes Characteristics

Rule 1 : When no voltage is applied, it acts like an openswitch.

Rule 2 : When an inversed voltage is applied, its

continues to act as an open switch (reversed-biased). Rule 3 : When a forward voltage is applied, it acts like a

closed switch and current flow from A to C (forward-biased).

Rule 4 : If current stop flowing, the diode returns to its

original open states.

Conducting in one direction and not in the other is theI-V characteristic of the diode.

The arrow-like circuit symbol shows the direction of

conducting current. Forward biasing voltage makes it turn on (ideal). Reverse biasing voltage makes it turn off (non-ideal).

Forward Bias (Current is permitted):

Small amount of voltage necessary to get the diode going. Isilicon, this voltage is about 0.7 volts. This voltage is needed to starthe hole-electron combination process at the junction

Reverse Bias (Current is prohibited):

Ideal diode would block all current. A real diode lets perhaps 1microamps through not a lot, but still not perfect. And if you appenough reverse voltage (V), the junction breaks down and letcurrent through. Usually, the breakdown voltage is a lot mor

voltage than the circuit will ever see, so it is irrelevant.

Function of Diodes

It conducts current in ONE direction only from Anode Cathode.

A diode is said to be forward biased when the anode is slightpositive with respect to the cathode and the diode conducts.

If the anode is negative with respect to the cathode a diodesaid to be reversed biased.

A diode can be used as a rectifier that converts AC (AlternatinCurrent) to DC (Direct Current) for a power supply device.

Diode can be used to separate the signals from radio frequencie

Diode can be used as an on/off switch that controls current.

Types of Diodes

PN JunctionDiodes:

Are used to allow

current to flow in onedirection while blockingcurrent flow in theopposite direction. Thepn junction diode is thetypical diode that has

been used in theprevious circuits.

Schematic Symbol for a PN

Junction Diode

Representative Structure for aPN Junction Diode

Types of Diodes

Zener Diodes:

Are specifically designed to operate

under reverse breakdown conditions.These diodes have a very accurate andspecific reverse breakdown voltage.

Schematic Symbol for a ZenerDiode

Types of Diodes

Schottky Diodes:

These diodes are designed to have a

fast switching time which makes thegreat diode for digital circuit applicatThey are very common in compubecause of their ability to be switcheand off so quickly.

Schematic Symbol for aSchottky Diode

Types of Diodes

Shockley Diodes:

The Shockley diode is a four-layer d

while other diodes are normally mwith only two layers. These typediodes are generally used to controaverage power delivered to a load.

Schematic Symbol for a four-layer Shockley Diode

Types of Diodes

Light-EmittingDiodes:

Light-emitting diodes are designed very large bandgap so movement of across their depletion region emits p

of light energy. Lower bandgap LEDsEmitting Diodes) emit infrared radwhile LEDs with higher bandgap energvisible light. Many stop lights arstarting to use LEDs because thextremely bright and last longer than bulbs for a relatively low cost.

Schematic Symbol for a Light-Emitting Diode

The arrows in the LEDrepresentation indicateemitted light.

Types of Diodes

Schematic Symbols forPhotodiodes

Photodiodes:

While LEDs emit light, Photodiodes are sensitreceived light. They are constructed so thejunction can be exposed to the outside through a

window or lens.In Photoconductive mode the saturation cincreases in proportion to the intensity of the relight. This type of diode is used in CD players.In Photovoltaic mode, when the pn junction is exto a certain wavelength of light, the diode gen

voltage and can be used as an energy source. Thof diode is used in the production of solar power.

Application of Diodes

Radio demodulation The first use for the diode was the demodulation of amplitudmodulated (AM) radio broadcasts. The history of this discoveis treated in depth in the radio article. In summary, an AM sign

consists of alternating positive and negative peaks of voltagwhose amplitude or “envelope” is proportional to the originaudio signal. The diode rectifies the AM radio frequency signaleaving an audio signal which is the original audio signal, minatmospheric noise. The audio is extracted using a simple filtand fed into an audio amplifier or transducer, which generat

sound waves.

Power conversion

We can construct rectifiers from diodes. They are used toconvert alternating current (AC) electricity into direct

current (DC).

Example : Automotive alternators, where the diode, whicconvert AC into DC, provides better performance than thecommutator of earlier dynamo.

Over-voltage protection Diodes are used to conduct damaging high voltages away frosensitive electronic devices. They are usually reverse-biased (noconducting) under normal circumstances. When the voltage rises, t

diodes become forward-biased (conducting).For example, diodes are used in motor controller and relay circuits de-energize coils rapidly without the damaging voltage spikes thwould otherwise occur. Many integrated circuits also incorporadiodes on the connection pins to prevent external voltages frodamaging their sensitive transistors. Diodes are used to protect froover-voltages at higher power.

Logic gates Diodes can be combined with other components to construct AND and ORlogic gates. This is referred to as diode logic

Temperature measurementsA diode can be used as a temperature measuring device, since the forwavoltage drop across the diode depends on temperature, as in a Silicbandgap temperature sensor. From the Shockley ideal diode, it appears tvoltage has a positive temperature coefficient (at a constant current) bdepends on doping concentration and operating temperature. Ttemperature coefficient can be negative as in typical thermistors or positifor temperature sense diodes down to about 20 kelvins. Typically, silicdiodes have approximately −2 mV/˚C temperature coefficient at roo

temperature.

END OF TOPIC 2

TOPIC 3: Transistors

Transistors

“The Transistor was probably the most important inventionof the 20th Century and the story behind the invention isone of clashing egos and top secret research.”

Ira Flatow

Transistors

Transistor is a 3 terminal electronic device made of semiconductomaterial.

It is a controllable current source.

An electronic device made of a semiconductor that can act as a

insulator and a conductor. The ability to change from these two states enables the device switch o

amplify.

Other uses including voltage regulation and the modulation of signals.

Transistors are central to the Integrated Circuit, and therefore, aelectronic devices of the information age, such as: pc’s, cellular phone

ipods, pda’s, intelligent cars and buildings…….. are made possible.

T i t ’ E l ti

Transistors’ Evolution

T i t ’ E l ti

Transistors’ Evolution

T f T i t

Types of Transistor

Bipolar Junction

Transistor(BJT)

Junction Field Effect

Transistor(JFET)

Metal-OxideSemiconductorFET(MOSFET)

Field EfTransis

Bi l J ti T i t (BJT

Bipolar Junction Transistor (BJT

BaseCollector

Emitter

Bipolar J nction Transistor (BJT

52Flyod (2001)

BJT is constructed with 3 doped semiconductregions separated by 2 P-N junctions.

The 3 regions called emitter base and collector.

The term Bipolar refers to the use of both holes aelectrons as charge carriers in the structure.

NPN BJT Transistor

High potential at collector

Low potential at emitter

Allows current flow whenthe base is given a highpotential

NPN BJT Transistor

The base-emitter diode(forward) acts as a switch.when v1>0.7 it lets the

electrons flow towardcollector. so we can control ouroutput current (Ic) with theinput current (Ib) by usingtransistors. Forwardbackward

PNP BJT Transistor

High potential at emitter

Low potential at collector

Allows current flow whenbase is connected to alow potential

Junction Field-Effect Transistor

(JFET)

BJT JFET

Collector Drain

Base Gate

Emitter Source

N/A Body

(JFET)

Field Effect Transistors, or FET's are unipolar rather thanbipolar devices.

It means that the main current through them is comprised

either of electrons through an N-type semiconductor or holethrough a P-type semiconductor.

FET can be divided into two main types: Junction-gatedevices called JFET's and Insulated-gate devices calledIGFET´s or more commonly known as MOSFET's (metal oxide

semiconductor FET)

(JFET)

The device terminals are the drain (D), GATE (G), source (S) andbody (B)

In normal operation, negligible current flows through the body

terminal. Sometimes, the body is connected to the source so thawe have three terminal device

The gate is insulated from the substrate by a thin layer of silicondioxide and negligible current flows through the gate terminal.

Metal-Oxide Semiconductor FET

(MOSFET)

The device terminals are the drain (D), GATE (G), source (S) and bod(B)

It can be divided into two types: Depletion and Enhancement (D and E

MOFSET). However, D-MOFSET can also be operated in Enhancement mode a

well while not for E-MOFSET.

The MOSFET operates in depletion when a negative gate-to-sourcvoltage is applied.

The MOSFET operates in depletion when a positive gate-to-sourcvoltage is applied.

(MOSFET)-D-MOSFET

(MOSFET)-E-MOSFET

Metal-Oxide Semiconductor FET( )

(MOSFET)

When the Gate is positive voltage ,it allows electrons toflow from drain to source .In this case transistor is on.

END OF TOPIC 3

Thyristors

In power electronics the choice of the switch to be used is always veryimportant for the designer.

This is specially important in automotive where the designer has tooptimize the numerous switching devices implemented for a wide field of

applications: ignition circuits, various electric motor controls, actuators insecurity systems

the thyristor must be considered as a low cost and powerful device formany functions in a car.

Thyristors

The thyristor is a four-layer, three terminal semiconducting device, with each layconsisting of alternately N-type or P-type material, for example P-N-P-N.

The main terminals, labeled anode and cathode, are across the full four layers, anthe control terminal, called the gate, is attached to p-type material near to th

cathode In fact the term "thyristor" defines a silicon bipolar semi-conductor family includin

any switch whose bistable action depends on PN-PN regenerative feed back. Thmain members of this family are the Silicone’s Controlled Rectifiers and the Triac. Othe other hand, this structure is also widely used in the new product famintegrating several "discrete“ components to build various power functions.

Thyristors

If a supply is connected across the device, and a small amount of current isinjected into the gate, then the device will "fire" and conduct.

It will remain in the conducting state until the supply is removed.

Thyristor has the ability to switch from off-state to on-state in response toa low gate current.

As soon as the latching current through the device is reached, the switchremains ON and the gate current can be removed. This "memory" effectcan be used in a broad area of applications, reducing the consumption ofdrivers and saving auxiliary components.

Triacs

Triode for Alternating Current can conduct current in either direction wheit is triggered (turned on).

It is formally called a bidirectional triode thyristor or bilateral triodthyristor.

Once triggered, the device continues to conduct until the current througit drops below a certain threshold value, the holding current, such as at thend of a half-cycle of alternating current (AC) mains power.

A TRIAC is approximately equivalent to two complementary unilaterthyristors (one is anode triggered and another is cathode triggered) joinein inverse parallel (paralleled but with the polarity reversed) and with the

gates connected together.

Triacs

TRIACs are usually seen in simple, low power applications likehousehold dimmer switches

Low power TRIACs also are used in many applications such asspeed controls for electric fans and other electric motors, and in

the modern computerized control circuits of many household smaand major appliances.

Triacs

TRIACs are usually seen in simple, low power applications likehousehold dimmer switches

Low power TRIACs also are used in many applications such asspeed controls for electric fans and other electric motors, and in

the modern computerized control circuits of many household smaand major appliances.

END OF TOPIC 4

TOPIC 5: Tranducers

Transducers

A transducer is a device that converts one type of energy tanother

The conversion can be to/from electrical, electro-mechanicaelectromagnetic, photonic, photovoltaic, or any other form o

energy. In electric circuit, transducer are used to produce a voltage ( o

sometimes a current) that is proportional to physical quantity ointerest, such as distance, pressure or temperature.

Transducers

Actuator

•An actuator acceptsenergy and producesmovement (action).

•The energy supplied toan actuator might beelectrical ormechanical

(pneumatic, hydraulic,etc.).

•An electric motor anda loudspeaker are bothactuators, convertingelectrical energy intomotion for differentpurposes

Sensor

•A sensor is used todetect a parameter inone form and report itin another form ofenergy (usually anelectrical and/or digitalsignal).

•For example, apressure sensor mightdetect pressure (amechanical form ofenergy) and convert itto electricity fordisplay at a remotegauge.

Combination

•Combinationtransducers have bothfunctions; they bothdetect and create action.

•For example, a typicalultrasonic transducerswitches back manytimes a second between

acting as an actuator toproduce ultrasonicwaves, and acting as asensor to detectultrasonic waves.

•Rotating a DC electricmotor's rotor willproduce electricity andvoice-coil speakers canalso act as microphones.

Transducers: Application

Antenna

converts electromagnetic waves into electric current and vice versa

Cathode ray tube (CRT)

converts electrical signals into visual form

Fluorescent lamp, light bulb

converts electrical power into visible light

Magnetic cartridge

converts motion into electrical form

Tape head

converts changing magnetic fields into electrical form

Transducers: Application

Loudspeaker/ earphone

converts electrical signals into sound

Microphone

converts sound into an electrical

Tactile transducer

converts solid-state vibrations into electrical signal

Piezoelectric crystal

converts solid-state electrical modulations into an electrical signal

Geophone

converts a ground movement (displacement) into voltage

Hydrophone

converts changes in water pressure into an electrical form

Conclusion

Semiconductor?

Diode?

Transistors? Thyristors and triacs?

Transducer?

week 4 chapter 3-electronic devices and transducers (2)

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