TRANSISTOR - Introduction and Electronics/F.Y.BSc Transistor.pdf · The input signal is applied to the base terminal and the output is taken from the emitter terminal. Collector terminal

TRANSISTOR

Mr. Kishor.S.Bonde

Department of Physics

Moolji Jaitha College, Jalgaon. (MS)

M.J.COLLEGE, JALGAON

Background

Invented at Bell Laboratories in 1947.

John Bardeen, Walter Brattain, and William Schockly received Nobel Prize in Physics in 1956 for Inventing Transistors.

First application: telephone signal amplification

Replaced cumbersome and inefficient vacuum tubes

Transistors can now be found on a single silicon wafer in most common electronic devices

Introduction

What are Transistors?• Versatile three lead semiconductor devices whose applications

include electronic switching and modulation (amplification)

• Transistors are miniature electronic switches.

• Configuration of circuit determines whether the transistor will serve a switch and amplifier

• Building blocks of the microprocessor, which is the brain of the computer.

• Have two operating positions- on and off.

• Binary functionality of transistors enables the processing of information in a computer.

Transistor Structure BJT is bipolar because both holes (+) and electrons (-) will take part in the

current flow through the device

N-type regions contains free electrons (negative carriers)

P-type regions contains free holes (positive carriers)

2 types of BJT

NPN transistor

PNP transistor

P

P

P

N

N

N

PNP and NPN transistor structure

IB(µA)

IB(µA)Ic(mA)

IE(mA) IE(mA)

IC(mA)

Arrow shows the current flowsArrow shows the current flows

NPN transistor:- A n p n transistor consist of thin p-type material sandwitched between two n-type matériel

PNP transistor:- A p n p transistor consist of thin n-type material sandwitched between two p-type matériel

The transistor regions are:

Emitter (E) – It is more heavily doped than other two region because it supplies charge carriers to the base send the carriers into the base region and then on to the collector

Base (B) – It is very thin(10-6m) as compare to emitter & collector & is very lightely doped. acts as control region. It can allow none , some or many carriers to flow

Collector (C) – Its main function is to collect the majority charge carriers through the base.

Collector

Base

Emitter

EB

C

PNP Schematic Symbol

Emitter

Base

Collector

Memory aid: NPN

means Not Pointing iN.

EB

C

NPN Schematic Symbol

N

P

NThe collector is lightly doped. C

The base is thin and

is lightly doped.B

The emitter is heavily doped. E

NPN Transistor Structure

TRANSISTOR BIASING

• Fundamental operation of pnp transistor and npn transistor is similar except for: – role of electron and hole, – voltage bias polarity, and – Current direction

For proper working of transistor, it is essential to apply voltage of correct polarity across its two junction The main condition;1) Emitter junction is always forward biased2) Collector junction is always reverse biased

Transistor configuration

Transistor configuration –is a connection of transistor to get variety operation.

3 types of configuration:

Common Base.

Common Emitter.

Common Collector.

Common-Base Configuration Base terminal is a common point for input and output.

Input – EB

Output – CB

Not applicable as an amplifier because the relation between input current gain (IE) and output current gain (IC) is approximately 1

Current amplification factor

It is the ratio of collector current to emitter current is called Current

amplification factor (α)

α =

Common-Emitter Configuration Emitter terminal is common for input and output circuit

Input – BE

Output – CE

Mostly applied in practical amplifier circuits, since it provides good voltage, current and power gain

Common-Collector Configuration The input signal is applied to the base terminal and the output is taken

from the emitter terminal.

Collector terminal is common to the input and output of the circuit

Input – BC

Output – EC

Input = Output

I-V Characteristic for CE configuration : Input characteristic

Input characteristic: input current (IB) against input voltage (VBE) for several output voltage (VCE)

From the graph IB = 0 A VBE < 0.7V (Si) IB = value VBE > 0.7V (Si)

The transistor turned on whenVBE = 0.7V

I-V Characteristic for CE configuration : Output characteristic

Output characteristic: output

current (IC) against output

voltage (VCE) for several

input current (IB)

3 operating regions:

Saturation region

Cut-off region

Active region

I-V Characteristic for CE configuration : Output characteristic

Saturation region – in which both junctions are forward-biased and IC increase linearly with VCE

Cut-off region – where both junctions are reverse-biased, the IB is very small, and essentially no IC flows, IC is essentially zero with increasing VCE

Active region – in which the transistor can act as a linear amplifier, where the BE junction is forward-biased and BC junction is reverse-biased. IC increases drastically although only small changes of IB.

Saturation and cut-off regions – areas where the transistor can operate as a switch

Active region – area where transistor operates as an amplifier

Current Relationships

Relations between IC and IE :α = IC

IE

Value of α usually 0.9998 to 0.9999, α ≈ 1

Relations between IC and IB :β = IC @ IC = βIB

IB

Value of β usually in range of 50 400 The equation, IE =IC + IB can also written in β

IC = βIB

IE = βIB + IB => IE = (β + 1)IB

The current gain factor , α and β is: α = β @ β = α .

β + 1 α - 1