Session 11 Introduction to bipolar junction transistor...

Session 11

Introduction to bipolar junction transistor (BJT)

Electronic Components and Circuits

José A. Garcia Souto

www.uc3m.es/portal/page/portal/dpto_tecnologia_electronica/Personal/JoseAntonioGarcia

Bipolar Junction Transistor

BJT

OBJECTIVESOBJECTIVES• Knowing the structure of the device and the transistor

effect

• Knowing and distinguishing basic parameters related to BJT transistors: α, β, hFB, hFE, ICBO, VBE(on), VCE(sat)

• Reading the current-voltage characteristic of the device

• Identifying the operating regions• Identifying the operating regions

Active, Cut-off, Saturation, Inverse Active

• Analyze basic cases in DC of BJT circuits

2UC3M 2010 CCE - Session 11

Bipolar Transistor Structure

n+ np

Emitter Base Collector

E Cn+ npE

B

C


p + pnE

B

C

Operation: Transistor Effect

p ++ pn

W

CiE

ip pn

E

B

Ch+

Bi

EBV

BCV

BCEIII +=

4

CBOECIII +⋅= α

CBOEBIII −⋅−= )1( α

1≈α

ECII ≈

UC3M 2010 CCE - Session 11

Characteristic parameters

• Physical Parameters

– α ECII ⋅≈ α 1≈α α

β =– α

– β

– ICBO

• Daasheet:

– hFB

ECII ⋅≈ α

BCII ⋅≈ β

CBOECIII +⋅= α

1≈α

1>>β α

αβ

−=1

CBOBCIII +⋅= β

Search BC547 in http://www.fairchildsemi.com/

I_Emitter I_Collector

I_Collector

I_Base– h

– hFE

– ICBO


I_Emitter I_Collector

Common-Base Common-Emitter

I_Base

Dual case: Transistor NPN

n ++ np

E CIe+

CiE

i

E

B

CIe+

Bi

BEV

CBV


n ++

n

p

BE C

6

IC (mA)

6 mA

Interpretation: current-voltage

characteristic

5

4

3

2

IE =4 mA

5 mA

3 mA

2 mA

1 mA

In ACTIVE the BC junction is OFF

The output current IC of the device is

contant even the VCB voltage changes

The IC current is determined by IE

In SATURATION the

BC junction is ON

The output voltage VCB

is constant even the IC

current changes

0 2 4 6 8 10 12 14 16

1 1 mA

VCB (V)

0 mA

The IC current is determined by IEcurrent changes


There is a curve for each input value IE

Operating RegionsRegion Base-Emitter Junction Base-Collector Junction

Cut-off Reverse(OFF) Reverse

Active Forward (ON) Reverse (Transistor Effect)Active Forward (ON) Reverse (Transistor Effect)

Saturation Forward (ON) Forward (Saturated)

Active Reverse Reverse Forward

Region Conditions NPN Operation NPN

Cut-off VBE < VBE-ON o IB = 0 IB=0, IC=IE=0

Active VBE-ON y VCE > VCE-SAT IC ≈ hFE·IB [VBE=VBE-ON]

8

Saturation VBE-ON y VCE-SAT VCE =VCE-SAT [VBE=VBE-SAT]

• Datasheet VBE(on) VCE(sat) hFE VBE(sat)



Output Characteristics

(Common - Emitter)

6

IC (mA)

60µA

5

4

3

2

1

IB =40µA

50µA

30µA

20µA

10µA

What input characteristic represent?


0µA

0 2 4 6 8 10 12 14 16

1 10µA

VCE (V)

Transfer Charateristic

60

IC (mA)

50

40

30

20

10


0 0,2 0,4 0,6 0,8

10

VBE (V)

What operating regions can be identified?

Example: Operating Regions

EXAMPLE

RC = 100 Ω CI

RC = 100 Ω

RB = …

VCC = 10 V

VBB = …

VBE(on) = 0,7 V

VCE(sat) = 0,2 V

hFE = 100

CI

EI

BI

BEV

CEV

11

Case 1 Case 2 Case 3 Case 4

VBB = 0 V IB = 0 VBB = 10 V VBB = 10 V

RB = 10 kΩ RB = 10 kΩ RB = 10 kΩ RB = 1 kΩ


Currents and Voltages of

NPN and PNP

CI

EI

BI

BEV

CEV

EI

I

EBV

ECV

BI

UC3M 2010 12CCE - Session 11

EI

CI

Operating RegionsCase of PNP transistor

• Datasheet VEB(on) VEC(sat) hFE VEB(sat)


Region Emitter-Base Junction Collector-Base Junction

Cut-off Reverse(OFF) Reverse

Active Forward (ON) Reverse (Transistor Effect)

Saturation Forward (ON) Forward (Saturated)


Region Conditions PNP Operation PNP

Cut-off VEB < VEB-ON o IB = 0 IB=0, IC=IE=0

Active VEB-ON y VEC > VEC-SAT IC ≈ hFE·IB [VEB=VEB-ON]

Saturation VEB-ON y VEC-SAT VEC =VEC-SAT [VEB=VEB-SAT]


Exercise: Operating Regions

DATA

RC = 100 Ω

RB = …

EI

BI V RB = …

VCC = 10 V

VBB = …

VEB(on) = 0,7 V

VEC(sat) = 0,2 V

hFE = 100 CI

BI

EBV

ECV

Case 1 Case 2 Case 3 Case 4

VBB = 0 V IB = 0 VBB = 10 V VBB = 10 V

RB = 10 kΩ RB = 10 kΩ RB = 10 kΩ RB = 1 kΩ


Proposed exercise

Voltages and currents

EI

CI

EBV

ECV

BI

15

Indicate what type of transistor is

Reasoning the operating region

Relate VB and VE, VB and IB, VE and IE, IE and IB.

Relate VC and IC


Session 11 Introduction to bipolar junction transistor...

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