what are and how are pnp npn transistor materials are made ?

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  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 1

    Transistor and their Characteristics

    Lesson-1 Junction Transistor

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 2

    1.1. Junction Transistor Junction Transistor Definition Definition

    The transferred-resistance or transistoris a multi-junction device that is capable of Current gain Voltage gain Signal-power gain

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 3

    Bipolar junction transistorBipolar junction transistorInvented in 1948 by Bardeen, Brattain and Shockley

    Contains three adjoining, alternately doped semiconductor regions: Emitter (E), Base (B), and Collector (C)

    The middle region, base, is very thin compared to the diffusion length of minority carriers

    Two kinds: npn and pnp

  • 2008 Junction Transistor Unit 4 Lesson 1-" , Raj Kamal, 4

    Bipolar junction transistor BJT Definition

    The Bipolar junction transistor is an active device that works as a voltage-controlled current source and whose basic action is control of current at one terminal by controlling voltage applied at other two terminals.

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 5

    Bipolar Junction Transistor Representation

    NPN PNP

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 6

    2.2. Transistor Current Transistor Current ComponentsComponents

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 7

    BJT circuit Current Components BJT circuit Current Components

    As shown, the currents are positive quantities when the transistor is operated in forward active mode.

    IE = IB + IC and VEB + VBC + VCE = 0 VCE = VEC

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 8

    Meaning of Forward biasingMeaning of Forward biasing

    When the p side is applied +ve and n side negative in a junction and applied voltage is grater than a threshold 0.65 V for Silicon (Si)

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 9

    Meaning of Reverse biasingMeaning of Reverse biasing

    When the p side is applied -ve and n side +ve in a junction and applied voltage is between 0 to a breakdown voltage

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 10

    3.3. Transistor as AmplifierTransistor as Amplifier

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 11

    BJT Common BJT Common Base Base

    configurationconfiguration

    BJT Common BJT Common EmitterEmitter

    configurationconfiguration

    BJT Common BJT Common Collector Collector

    configurationconfiguration

    PNPPNP PNP

    IB IE IC

    Three configurations

  • 2008 Junction Transistor Unit 4 Lesson 1-" , Raj Kamal, 12

    Six Problems

    Draw circuits of CB, CE, CC configurations for npn and pnp transistors Show current directions

  • 2008 Junction Transistor Unit 4 Lesson 1-" , Raj Kamal, 13

    npn transistor in a simple circuit, known ascommon-emitter amplifier

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 14

    Characteristics ofCharacteristics of Transistor Amplifier in three Transistor Amplifier in three regions of operations regions of operations

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 15

    Input or driving Point Input or driving Point Characteristics of Common Characteristics of Common Base transistor AmplifierBase transistor Amplifier

    Input or driving Point Characteristics of Common Emitter transistorAmplifier

    Active region

    Saturation region Saturation region

    Active region

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 16

    Output Collector Output Collector Characteristics of Common Characteristics of Common Base transistor AmplifierBase transistor Amplifier

    Output Collector Output Collector Characteristics of Common Characteristics of Common

    Emitter transistorEmitter transistorAmplifierAmplifier

    Saturation region Cut-off region Cut-off regionSaturation region

    Active region Active region

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 17

    First Approximation Relationship First Approximation Relationship between between IICC and and IIEE

    IC IEBJT Common BJT Common

    Base Base configurationconfiguration

  • 2008 Junction Transistor Unit 4 Lesson 1-" , Raj Kamal, 18

    The collector current is being controlled by the B-E voltage, orthe current in the one part of the device is being controlled bythe voltage in another part - transistor action

    Since the B-E junction is forward biased, holes from the baseare injected into the emitter. However, these injected holesdo not contribute to the collector current and are thereforenot part of the transistor action

    To design a useful device, we need mathematical expressionsfor the minority carrier concentrations shown in the figureabove.

    There are three modes of operation we must consider

    Forward-active (B-E FB, B-C RB) Cut-off (B-E RB, B-C RB) Saturation (B-E FB, B-C FB)

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 19

    BJT biasing modesBJT biasing modes

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 20

    In the cut-off region, the base emitter and collector base junctions of transistor are reverse biased IC IE 0

    CutCut--off defined as region of characteristics Ioff defined as region of characteristics ICC = 0= 0

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 21

    Saturation- region defined as region of characteristics left of VCB = 0 and IC increase

    exponentially with VCB increases toward 0

    In the saturation region region, the base emitter and collector base junctions of transistor are forward biased

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 22

    Active - region defined as region of characteristics right of VCB = 0 and IC first increases exponentially with VCB increases toward 0.7 V in Si transistor and then becomes constant In the active region region, the base emitter and

    collector base junctions of transistor are forward and reversed biased respectively IC IE 0 and is in mA IC

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 23

    Operation in the forward-activemode

    B-E junction is forward biased so electronscan be injected from the emitter to the base, B-Cjunction is reverse biased.

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 24

    4.4. Transistor Transistor Construction Construction

  • 2008 Junction Transistor Unit 4 Lesson 1-" , Raj Kamal, 25

    BJT structure - three regions, two p-n junctions, threeterminals (emitter, base, collector)

    ThinThin

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 26

    Construction Construction Devices can be p-n-p, or n-p-n structures Width of the base is small compared to the

    minority carrier length and is about 1/150 of total width, number of free carriers are small as doping level is 1/10 th or less compared to collector)

    Emitter is normally heavily doped, the collector has light doping

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 27

    SummarySummary

    We learnt (i) pnp transistor (ii) npn transistor (iii) Current Components (iv) Three configurations-

    Common base, common emitter and Common collector

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 28

    We learnt (v) Three regions- cut-off,

    saturation and active (vi) Transistor construction

  • 2008 Junction Transistor Unit 4 Lesson 1- " , Raj Kamal, 29

    End of Lesson 1End of Lesson 1

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