ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc. Lecture 27 Bipolar Junction Transistors.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Lecture 27Bipolar Junction Transistors


Bipolar Junction Transistors

1. Understand bipolar junction transistor operation in amplifier circuits.

2. Analyze simple amplifiers using the load-line technique and understand the causes of nonlinear distortion.


Tubes


Deforest’s Audion


Triode Tube


Bardeen, Brittain and Shockley

Discovery of the transistor in 1947


First Transistor


Initial Demonstration of Solid State Amplification



First Integrated Circuit (IC)

Jack Kilby at Texas Instruments (1958)


Early Integrated Circuit (IC)


Chip Evolution


NPN and PNP Bipolar Junction Transistors (BJT)

http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm


NPN Bipolar Junction Transistor


Bias Conditions for PN Junctions

The base emitter p-n junction of an npn transistor is normally forward biased

The base collector p-n junction of an npn transistor is normally reverse biased


Bias Conditions for NPN Junctions












Equations of Operation

1exp

T

BEESE V

vIi

BCE iii

From Kirchoff’s current law:



E

C

i

i

Define as the ratio of collector current to emitter current:

Values for range from 0.9 to 0.999 with 0.99 being typical. Since:

EBBEBCE iiiiiii 01.099.0

Most of the emitter current comes from the collector and very little (1%) from the base.



1exp

T

BEESC V

vIi

1exp

T

BEESE V

vIi

E

C

i

i


1exp)1(

T

BEESB V

vIi

)1(1

EE

CECEB

BCE

ii

iiiii

iii




1B

C

i

i

Define as the ratio of collector current to base current:

Values for range from about 10 to 1,000 with a common value being 100.

BC ii

The collector current is an amplified version of the base current.



1exp

T

BEESE V

vIi

1exp

T

BEESC V

vIi 99.0

E

C

i

i

1exp)1(

T

BEESB V

vIi

BC ii 1001

B

C

i

i


Only a small fraction of the emitter current flows into the base provided that the collector-base junction is reverse biased and the base-emitter junction is forward biased.

The base region is very thin


Exercise 13.1A certain transistor has = 50, IES = 10-14A, vCE = 5 V, and iE = 10 mA. Assume VT = 0.026 V. Find vBE, vBC, iB, iC and .

AmAi

i

mAii

VVVvvv

mVmVI

iVv

V

vIiIi

V

vIi

CB

EC

CEBEBC

ES

ETBE

T

BEESE

T

BEESE

19650

80.9

80.9

980.051

50

1

282.45718.0

4.71810

10ln26ln

expwith operation For 1exp

14

2

ESE


Exercise 13.2Compute the corresponding values of if = 0.9, 0.99 and 0.999

999999.01

999.0

9999.01

99.0

99.01

9.01

999.0

99.0

9.0


Exercise 13.3A certain transistor operated with forward bias of the base-emitter junction and reverse bias of the base-collector junction has iC = 9.5 mA and iE = 10 mA. Find the value of iB, and .

19

95.010

5.9

5.0

B

C

E

C

CEB

i

i

mA

mA

i

i

mAiii


Common-Emitter Characteristics

biasreversevvif v

vvv

BCBECE

CEBEBC

0

vBC

vCE


Common-Emitter Input Characteristics

1exp)1(

T

BEESB V

vIi


Common-Emitter Output Characteristics

100 forii BC


Amplification by the BJT

A small change in vBE results in a large change in iB if the base emitter is forward biased. Provided vCE is more than a few tenth’s of a volt, this change in iB results in a larger change in iC since iC=iB.


Common-Emitter Amplifier


Load-Line Analysis of a Common Emitter Amplifier (Input Circuit)

tvtiRtvV BEBBBB in


CECCCC viRV

Load-Line Analysis of a Common Emitter Amplifier (Output Circuit)


As vin(t) goes positive, the load line moves upward and to the right, and the value of iB increases. This causes the operating point on the output to move upwards, decreasing vCE An increase in vin(t) results in a much larger decrease in vCE so that the common emitter amplifier is an inverting amplifier

Inverting Amplifier


Load-Line Analysis of BJTAssume VCC = 10V

VBB = 1.6V

RB = 40 k

RC = 2 k

Vin = 0.4sin(t)

iBQ = 25 A

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

4040

6.100

6.100

406.1



VBB = 1.6V

RB = 40 k

RC = 2 k

Vin = 0.4sin(t)

iBmax= 35 A

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

5040

24.00

24.00

406.1



VBB = 1.6V

RB = 40 k

RC = 2 k

Vin = 0.4sin(t)

iBmin= 15 A

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

3040

2.14.00

2.14.00

406.1


VCEQ = 5V

iCEQ = 2.5 mA

VCEQ = 5V

VCEmin = 3V

VCEmax = 7V

CEC vik 210

Load-Line Analysis of BJTiBQ = 25 A

iBmin= 15 A

iBmax= 35 A


Load-Line Analysis of BJT

Voltage waveforms for the common emitter amplifier. The gain is -5 (inverting).


When iC becomes zero, we say that the transistor iscutoff.

When vCE 0.2 V, we say that the transistor is in saturation.

Clipping

Amplification occurs in the active region. Clipping occurs in the saturation or cutoff regions.


Clipping


Exercise 13.5

min

max

CE

CEQCE

V and

V,V Find

)sin(8.0)( ttvin Ai

QB 25

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

4040

6.100

6.100

406.1


min

max

CE

CEQCE

V and

V,V Find

)sin(8.0)( ttvin

Exercise 13.5

AiB 45max

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

6040

4.28.00

4.28.00

406.1


min

max

CE

CEQCE

V and

V,V Find

)sin(8.0)( ttvin

Exercise 13.5

AiB 5min

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

2040

8.08.00

8.08.00

406.1


Exercise 13.5

mAiVVAi

mAiVVAi

mAiVVAi

CCEB

CCEB

CCEBQ QQ

5.4145

5.095

5.2525

maxminmax

minmaxmin


Exercise 13.6

V

ttvin

2.1V

)sin(8.0)(

BB Ai

QB 15

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

3040

2.100

2.100

402.1


Exercise 13.6

V

ttvin

2.1V

)sin(8.0)(

BB AiB 35

max

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

5040

28.00

28.00

402.1


Exercise 13.6

V

ttvin

2.1V

)sin(8.0)(

BB AiB 1

min

Ak

Vivandv

vvandi

vikv

tvtiRtvV

BinBE

BEinB

BEBin

BEBBinBB

1040

4.08.00

4.08.00

402.1


Exercise 13.6

mAiVVAi

mAiVVAi

mAiVVAi

CCEB

CCEB

CCEBQ QQ

5.3335

0.18.91

5.1715

maxminmax

minmaxmin


PNP Bipolar Junction Transistor

Except for reversal of current directions and voltage polarities, the pnp BJT is almost identical to the npn BJT.


PNP Bipolar Junction Transistor

BCE

BC

EB

EC

iii

ii

ii

ii

)1(


Common-Emitter Characteristics for a PNP BJT

1exp)1(

1exp

T

EBESB

T

EBESE

V

vIi

V

vIi


Exercise 13.7

Find :

5050

5.2

A50i2.5mAi 6V,VFor BCCE

A

mA

i

i

B

C


Exercise 13.8

Common emitter amplifier

080008.0 BEBin viv


Exercise 13.8

Aivv

viv

Aivv

viv

Aivv

viv

viv

BBEin

BEBin

BBEin

BEBin

BBEin

BEBin

BEBin

1258000

102.0

102.0

758000

6.002.0

6.002.0

1008000

8.000

8.000

080008.0


Exercise 13.8

Ai

Ai

Ai

B

B

BQ

5

48

24

min

max


Common emitter amplifier

CCE

CEC

iv

vi

30009

030009

Exercise 13.8


mAiv

vi

iv

CCE

CEC

CCE

33000

90

90

30009

Exercise 13.8

Load line:


Exercise 13.8

VVAi

VVAi

VVAi

QQ

in

CEB

CEB

CEB

3.524

3.85

8.148

min

maxmax

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc. Lecture 27 Bipolar Junction Transistors.

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