bjt, bipolar junction transisor

1

BJT, Bipolar Junction Transisor

Bollen

Base CurrentBase Current

ControlsControls

Output currentOutput current

2

AGENDA

Bollen

BJT transistormanTransistor typesBipolar Junction TransistorBJT modelsparameterswater modelNPN and PNPoperation modesswitch openswitch closed

BJTlinear, controlled current sourceactive operationcharacteristicsDC input characteristicsac input characteristicsBJT DC biasing circuitsbase biasbase bias + collector feedbackbase bias + emitter feedbackvoltage divider

3

BJT, transistor man

Bollen

4

TransistorTypes

Bollen

Output currentOutput current controlled controlled

by by input currentinput current

Output currentOutput current controlledcontrolled

by by input voltageinput voltage

BJT ==

Bipolar Junction Bipolar Junction TransistorTransistor

FET ==

Field Effect TransistorField Effect Transistor

5


Bollen

BE ForwardBE Forward bias, bias, BC ReverseBC Reverse bias bias

So So lowlow ohmic ohmic highhigh ohmic ohmic

TransistorTransistor == TranTransfersfer ReResistorsistor

6


Bollen

Emitter Emitter = Sent = Sent electronselectrons

BaseBase = Base = Base

CollectorCollector = Get = Get electrons electrons

7

BJT, Models

Bollen

8

BJT, parameters

Bollen

9

BJT, Water model

Bollen

10

BJT, Water model

Bollen

11

BJT, NPN and PNP

Bollen

12

BJT, Operation modes

Bollen

Cut-off and Cut-off and saturation;saturation;

BJT is used as a BJT is used as a switchswitch

Active operationActive operation

Quiecent Point;Quiecent Point;

BJT is used as a BJT is used as a

controlled controlled

current source,current source,

or or analog amplifieranalog amplifier

13

BJT, Switch open

Bollen

14

BJT, Switch closed

Bollen

15

BJT, Lineair, controlled current source

Bollen

16

BJT, active operation

Bollen

17

BJT, characteristics

Bollen

DCDC model model acac model model

DCDC model; Vbe = 0V7 Ube, Uce, Ic, Ib, Ie model; Vbe = 0V7 Ube, Uce, Ic, Ib, Ie CapitalsCapitals

acac model; re = 26mV/Ie ube, uce, ic, ib, ie model; re = 26mV/Ie ube, uce, ic, ib, ie Low Low casescases

18

BJT, DC input characteristics

Bollen

Vbe = 0V7

19

BJT, AC input characteristics

Bollen

re = 26mV/Ic

The dynamic resistor can be calculated by the DC current

Ic

20

BJT, characteristics

Bollen

21

BJT, DC biasing circuits

Bollen

A base biasA base bias

B base bias + emitter feedbackB base bias + emitter feedback

C base bias + collector feedbackC base bias + collector feedback

D voltage dividerD voltage divider

22

BJT, base bias, introduction

Bollen

Base current determined by Vcc, Rb and Vbe

23

BJT, base bias

Bollen

cc Rb beV U U

cc b b beV I R U

c bI I Calculate Ib and then Ic

Ic directly dependent on ß variation

So, for stability a “bad” circuit

24

BJT, base bias load line

Bollen

Load line is the loading of the transistor seen from Uce (>0V7)

Vcc and Rc determines the; “open voltage” and the “short circuit current”

Q-point = Quiecient

point= Working point

25


Bollen


Vcc and Rc determines the; “open voltage” and the “short circuit current”

Reliable circuit= Q-point

stability

26


Bollen

Vce always > 0V7BC junction

REVERSE

If Rc too big, transistor in saturation; then;

27


Bollen

Vce always > 0V7BC junction

REVERSE

If Vcc too small, transistor in saturation; then;

28

BJT, base bias example

Bollen

Calculate;

Ib, IcURc, Uc, Uce

Draw output caracteristic

Calculate now;

Uce if ß = 40How many % did Uce

ChangeIb = 47 uA, Ic = 2,35 mA, URc = 5,17 V, Uc = 6,83 V, Uce = 6,83 VUce (for ß = 40) = 7,86 Ξ 15 %

29


Bollen

Ib = 33 uA, Ic = 2,9 mA URc = 7,9 V, Uc = 8,1 V

Rb = 282,5 kΩ, Ic = 3,2 mA,

Rc = 1,855 kΩ

30


Bollen

ß = 200, VRc = 8,8 VVcc = 16 VRb = 765 kΩ

31

BJT, base bias + emitter feedback

Bollen

Base current determined by Vcc, Rb, Vbe and Ve

More stable for ß variations, than base bias.

32


Bollen

Always calculate in the smallest current Ib !!

Recc Rb beV U U U

Re1cc b b be bV I R U I U

Rc c cV I R

c cc c cV V I R

e e eV I R

ce c eV V V

33


Bollen


Vcc, Rc and Re determines the; “open voltage” and the “short circuit current”

34

BJT, base bias + emitter feedback example

Bollen

Calculate;

Ib, IcURc, Uc, Ue, Uce


Ib = 6,2 uA, Ic = 0,74 mA, URc = 8,9 V, Uc = 7,1 V, Ue =-0,9 V, Uce = 8,0 V

35

BJT, base bias + emitter feedback example

Bollen

Calculate;

Ib, IeURe, Ue, Uce


Ib = 24 uA, Ie = 2,9 mA, URc = 3,5 V, Ue = -2,5 V, Uce = 2,5 V

36

BJT, base bias + collector/emitter feedback

Bollen

If Ic > then Uc < then Ib <

If Ic > then Uc <and Ue > then Ib <

37

BJT, base bias + collector feedback

Bollen

cc Rc Rb beV U U U

1cc b c b b beV I R I R U


The current through Rc is not Ic but Ic + Ib,

so (β+1)Ib !!!

If Ic rises for any reason, then Uc falls and

also Ib decreases, so then Ic decreases

38

BJT, base bias collector feedback example

Bollen

Calculate;

Ib, ß, Ic


Ib = 13 uA, ß = 196, Ic = 2,5 mA

39

BJT, base bias collector/emitter feedback

Bollen

Recc Rc Rb beV U U U U

1

1

cc b c

b b

be

b e

V I R

I R

U

I R


40

BJT, base bias collector/emitter feedback ex

Bollen

Calculate;

Ib, IeURc, Uc, Ue, Uce


Ib = 11,8 uA, Ie = 1,1 mA

URc = 5,2 V, Uc = 4,8 V

Ue = 1,3 V, Uce = 3,5 V

41

BJT, voltage divider

Bollen

Vb is a stable voltage - 0,7 V =

so Ve is a stable voltageIe is determined by Ve/ Re

Ic = Ie . ß/(ß+1)

Ic is very stable and nearly independent to ß

variation, as long as ß is BIG in value

2 methods of calculating Ic - neglegting Ib, use voltage divider - not neglecting Ib and use thevenin

42

BJT, voltage divider, neglect Ib

Bollen

2

1 2b cc

RV V

R R

0 7e bV V V

ee

e

VI

R

1c eI I

So neglegt Ib to R2, or in general Ri >> R2In practice 10 times bigger

43

BJT, voltage divider, exact, thevenin

Bollen

Thevenin resistance

R1 // R2 62k // 9k1= 7k9

Thevenin voltage 2

1 2th cc

RV V

R R

9 116 2 0

62 9 1th

kV V

k k

44

BJT, voltage divider, exact, thevenin

Bollen

2V0

7k9

1th b th be b eV I R V I R

2,0 7 9 0,7 80 1 0,68b bI k I k Ib = 20 uA

45

BJT, voltage divider, example

Bollen

Thevenin resistance = 6k8

Thevenin voltage = 3V1

Ib = 18,8 uAIc = 2,25 mAre = 11,5 ΩURc = 7V4Uc = 10V6Ue = 2V3Uce = 5V1

46

BJT, voltage divider, example

Bollen

Thevenin resistance = 255k

Thevenin voltage = 0V0

Ib = 14,3 uAIc = 1,9 mAre = 14 ΩURc = 17V3Uc = 0V7Ue = -3V7Uce = 4V4

47

BJT

Bollen

48

BJT

Bollen

bjt, bipolar junction transisor

Documents