Seminar Amaljo Joju E EEE

TOPIC: TRANSISTOR

What is a transistor ?• A Transistor is a semiconductor device

used to amplify and switch electronics signals and electrical power supply

• An electronic device made of a semiconductor that can act as an insulator and a conductor.

• Transistors are central to the Integrated Circuit, and therefore, all electronic devices of the information age, such as: pc’s, cellular phones, ipods, pda’s, intelligent cars and buildings…….. are made possible

Transistor is known as WONDER BABY IN ELECTRONICS

It is the fundamental bulding blocks of modern electronic devices

Transistor is a 3 terminal device

It is represented by →→

Evolution of TRANSISTOR

Before transistors were invented, circuits used VACUUM TUBES:

Fragile, large in size, heavy, generate large quantities of heat, require a large amount of power

1895 John Ambrose Fleming

-developed the Vacuum Tube

a device that modify a signal by controlling the movement of electrons in an evacuated space.

The electrons flow only from filament to plate creating a diode (a device that can conduct current only in one direction)

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1946 –John Eckert & John W. Mauchly – ENIAC 1 Computer

ENIAC was short for Electronic Numerical Integrator And Computer. It was the first general purpose (programmable to solve any problem) electric computer. It contained over 17,000 vacuum tubes, weighed 27 tones and drew 150 kW of power to operate.

Aug 20 2007

1947 The first integrated transistor (Bell Telephone Laboratories)

Bardeen and Brattain built the point contact transistor.They made it from strips of gold foil on a plastic triangle, pushed down into contact with slab of germanium

1947 cont. Shockley make the

Junction transistor (sandwich).

This transistor was more practical and easier to fabricate.

The Junction Transistor became the central device of the electronic age

http://www.ecse.rpi.edu/Homepages/schubert/Unused%20stuff/Educational%20resources/Picture%20First%20junction%20transistor.jpg

1948 They decided to name it transistor

instead of Point-contact solid state amplifier

Foundation of Shockley Semiconductor, sowing the seeds of silicon valley

1958 cont. - Integrated Circuit

A single device that contains an interconnected array of elements like transistors, resistors, capacitors, and electrical circuits contained in a silicon wafer.

Just refresh………

• Doping: adding small amounts of other elements to create additional protons or electrons

• P-Type: dopants lack a fourth valence electron (Boron, Aluminum)

• N-Type: dopants have an additional (5th) valence electron (Phosphorus, Arsenic)

• Importance: Current only flows from P to N

• Diode: simple P-N junction.

• Forward Bias: allows current to flow from P to N.

• Reverse Bias: no current allowed to flow from N to P.

• Breakdown Voltage: sufficient N to P voltage of a Zener Diode will allow for current to flow in this direction.

Transistor types

MOS - Metal Oxide Semiconductor

FET - Field Effect Transistor

BJT - Bipolar Junction Transistor

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Architecture of BJTs The bipolar junction transistor

(BJT) is constructed with three doped semiconductor regions separated by two pn junctions

Regions are called emitter, base and collector

There are two types of BJTs, the npn and pnpThe two junctions are termed the base-emitter junction and the base-collector junctionThe term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structureIn order for the transistor to operate properly, the two junctions must have the correct dc bias voltages

npn BJT Transistors• High potential at

collector• Low potential at

emitter• Allows current flow

when the base is given a high potential

pnp BJT Transistors

• High potential at emitter• Low potential at collector• Allows current flow when

base is connected to a low potential

BJT npn Transistor

1 thin layer of p-type, sandwiched between 2 layers of n-type.

N-type of emitter: more heavily doped than collector. With VC>VB>VE: Base-Emitter junction forward biased, Base-Collector

reverse biased. Electrons diffuse from Emitter to Base (from n to p). There’s a depletion layer on the Base-Collector junction

no flow of e- allowed. BUT the Base is thin and Emitter region is n+ (heavily

doped) electrons have enough momentum to cross the Base into the Collector.

The small base current IB controls a large current IC

Architecture of MOS Field-Effect Transistors (FETs)

• The metal-oxide semiconductor field-effect transistor (MOSFET) : the gate is insulated from the channel by a silicon dioxide (SiO2) layer

Field Effect Transistors Three Types of Field Effect Transistors MOSFET (metal-oxide-semiconductor

field-effect transistors) JFET (Junction Field-effect transistors) MESFET (metal-semiconductor field-effect

transistors)

Other Types of Transistors

Various Types of Transistors TempFET – MOSFET’s with temperature

sensor

High Electron Mobility Transistors (HEMTs) – allows high gain at very high frequencies

Darlington – two transistors within the same device, gain is the product of the two inidvidual transistors

Shockley Diode/Thyristor Four-layer PNPN semiconductor devices Behaves as two transistors in series Once on, tends to stay on Once off, tends to stay off

TRIAC Triode alternating current switch Essentially a bidirectional

thyristor Used in AC applications Con: Requires high current to

turn on Example uses: Modern dimmer

switch

Used as…………….

Switching Amplification

Variable Resistor

Questionzzz

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