Ch8 ทรานซิสเตอร์

  • View
    158

  • Download
    1

Embed Size (px)

Text of Ch8 ทรานซิสเตอร์

  • 353152 1,

    8 ( BIPOLAR JUNCTION TRANSISTORS )

  • 353152 1

    Motivation

    ( BIPOLAR JUNCTION TRANSISTORS )

  • 353152 1

    PN 2 (Bipolar Junction Transistor) BJT

  • 353152 1

    3

    ( Base : B ) ( Emitter : E ) ( Collector : C ) 2

    1) ( PNP )

    2) ( NPN )

  • 353152 1

    3 3

    1. (Common Base) 2. (Common Collector) 3. (Common Emitter)

  • 353152 1

    1. (Common Base)

  • 353152 1

    ( )() 3

    ()

    ( )() ( ) 1. (Cut-off Region) : 2. (Saturation Region) : 3. (Active Region) :

    1. (Common Base)

  • 353152 1

    1. (Common Base)

    (Cut-off)

    (Saturation)

    EC II

  • 353152 1

    1. (Common Base Configuration) ON

    = 0.7 (C)

    10

  • 353152 1

    Common Base

  • 353152 1

    Example 1(a) IE= 3 mA VCB= 10 V.(b) IE = 3 mA VCB = 2 V.(c) VBE IC= 4 mA VCB=20 V.(d) (c) 10(c).

    (a) (b) VCB IC 3 mA (c) VBE 0.74 V.(d) 10(c), VBE 0.7 V

    11

  • 353152 1

    1. (Common Base Configuration)

    Alpha () IC IE : =1 : 0.9 0.998

    Alpha ()

    E

    Cdc

    I

    I

    COBEC III

    constant

    CBVE

    Cac

    I

    I

  • 353152 1

    Transistor Amplifier Action

    20 Voltage amplification:

    V 50)k 5)(mA 10(

    mA 10

    RL

    IL

    V

    iI

    LI

    EI

    CI

    iR

    iV

    iI 10mA20

    200mV

    Currents and Voltages:

    250200mV

    50V

    iV

    LV

    vA

    The combination of the two terms in italics results in the label transistor; that is, transfer + resistor transistor.

  • 353152 1

    1. (Common Base Configuration)

    Beta () IC IB beta :

    50 400 :

    represents the amplification factor of a transistor. ( is sometimes referred to as hfe, a term used in transistor modeling calculations)

    B

    Cdc

    I

    I

    constant

    CEVB

    Cac

    I

    I

  • 353152 1

    factors and

    1. (Common Base Configuration)

    108

    A 25

    mA 2.77.5Vdc CE

    B

    C

    I

    I

    100

    A 10

    mA 1

    A) 20 A (30

    mA) 2.2mA (3.2

    7.5V

    ac

    CE

    constantCEVB

    C

    I

    I

    1

    1

    BC II BE 1)I(I

  • 353152 1

    2.(Common-Emitter Configuration) pnp

    npn

    (base-emitter) (collector-emitter).16

  • 353152 1

    active reverse-biased - forward-biased

    active voltage, current, or power amplification.

    cutoff IC IB

    17

    2.(Common-Emitter Configuration)

  • 353152 1

    2.(Common-Emitter Configuration)

    AI

    CBOCEO

    B

    II

    01

    ICBO = minority collector currentICBO is usually so small that it can be ignored, except in high power transistors and in high temperature environments.

  • 353152 1

    Example 2(a) Using the characteristics of Fig. 14, determine IC at IB=30 A and VCE=10 V.(b) Using the characteristics of Fig. 14, determine IC at VBE=0.7 V and VCE=15 V.

    (a) At the intersection of IB=30 A and VCE=10 V, IC =3.4 mA (b) Using Fig. 14(b), IB=20 A at VBE=0.7 V. From Fig. 14(a) we find that IC =2.5 mA at

    the intersection of IB=20 A and VCE=15 V.19

  • 353152 1

    3. (Common Collector Configuration)

  • 353152 1

    (IB) () ()

    =

    = = 200 50= 10mA

    = +

  • 353152 1

  • 353152 1

    VCE IC (ICmax= ICEO) (Cutoff region) IC VCE (VCE max = VCEsat = VCEO) (saturation region) The transistor operates in the active region between saturation and cutoff.

    Common-emitter:

    Common-base:

    Common-collector:

    23

    CCECmax IVP

    CCBCmax IVP

    ECECmax IVP

  • 353152 1

    Transistor Specification Sheet The information provided as Fig. is taken directly from the Small-Signal

    Transistors, FETs, and Diodes publication prepared by Motorola Inc.

    Note in the maximum rating list that VCEmax=VCEO=30 V with Icmax=200 mA. The maximum collector dissipation Pcmax=PD=625 mW.

    The specification sheet can be a very valuable tool in the design or analysis mode Every effort should be made to be aware of the importance of each parameter and

    how it may vary with changing levels of current, temperature, and so on.24

  • 353152 1

    TransistorCurve Tracer

    Provides a graph of the characteristic curves.

    DMM Some DMMs measure DC or hFE.

    Ohmmeter

    25

  • 353152 1

    Transistor Casing and Terminal Identification The entire structure of transistor is encapsulated in a container such as that shown in Fig. 3.29. Those with the heavy duty construction are high-power devices, while those with the small can (top hat) or plastic

    body are low- to medium-power devices.

    26

  • 353152 1

  • 353152 1

    1

  • 353152 1

    1. IE= 4.5 mA VCB= 4 V2. 1 IE= 4.5 mA VCB= 16 V3. .

    4. Using the characteristics of Fig 2. 1. Determine ICEO at VCE = 10 V.2. Determine dc at IB =10 mA and VCE = 10 V.3. Using the dc determined in part (b), calculate ICBO.

  • 353152 1

    2

  • 353152 1

    8 5.