Bi l J ti T i tBipolar Junction Transistor(BJT)(BJT)

Sub Title :Transistor CharacteristicsTransistor Characteristics

Introduction

A bipolar transistor consists of a three-layer "sandwich" of doped (extrinsic)layer sandwich of doped (extrinsic)semiconductor materials, either P-N-Por N-P-N. Each layer forming theor N P N. Each layer forming thetransistor has a specific name, and eachlayer is provided with a wire contact forlayer is provided with a wire contact forconnection to a circuit.

Introduction

IntroductionThe only functional difference between a PNP transistorand an NPN transistor is the proper biasing (polarity) ofthe junctions when operating. For any given state ofoperation the current directions and voltage polarities foroperation, the current directions and voltage polarities foreach type of transistor are exactly opposite each other.Bipolar transistors work as current-controlled currentregulators. In other words, they restrict the amount ofregulators. In other words, they restrict the amount ofcurrent that can go through them according to a smaller,controlling current. The main current that is controlledgoes from collector to emitter, or from emitter tocollector depending on the type of transistor it is (PNP orcollector, depending on the type of transistor it is (PNP orNPN, respectively). The small current that controls themain current goes from base to emitter, or from emitterto base, once again depending on the type of transistor it, g p g ypis (PNP or NPN, respectively).

IntroductionAccording to the confusingstandards of semiconductorsymbology, the arrow alwayspoints against the direction ofp gelectron flow:Bipolar transistors are calledbipolar because the main flowof electrons through them takesl i t t fplace in two types of

semiconductor material: P andN, as the main current goesfrom emitter to collector (or viceversa). In other words, twoversa). In other words, twotypes of charge carriers {electrons and holes { comprisethis main current through thetransistor.

Transistor as A SwitchBecause a transistor's collectorcurrent is proportionally limited byits base current, it can be used as

t f t t ll d it ha sort of current-controlled switch.A relatively small flow of electronssent through the base of thetransistor has the ability to exerttransistor has the ability to exertcontrol over a much larger flow ofelectrons through the collector.Suppose we had a lamp that wewanted to turn on and or by meanswanted to turn on and or by meansof a switch. Such a circuit would beextremely simple:

Transistor as A SwitchFor the sake of illustration, let's inserta transistor in place of the switch toshow how it can control the flow ofl t th h th lelectrons through the lamp.

Remember that the controlledcurrent through a transistor must gobetween collector and emitter. Sincebetween collector and emitter. Sinceit's the current through the lamp thatwe want to control, we must positionthe collector and emitter of ourtransistor where the two contacts oftransistor where the two contacts ofthe switch are now.

Transistor as A Switch

In this example Ihappened to choose anNPN transistor. A PNPtransistor could also haveb h f th j bbeen chosen for the job,and its application wouldlook like this:look like this:

Transistor as A SwitchGoing back to the NPN transistor in ourexample circuit, we are faced with theneed to add something more so thatwe can have base current Without awe can have base current. Without aconnection to the base wire of thetransistor, base current will be zero,and the transistor cannot turn on,resulting in a lamp that is always orresulting in a lamp that is always or.Remember that for an NPN transistor,base current must consist of electronsflowing from emitter to base (againstthe emitter arrow symbol just like thethe emitter arrow symbol, just like thelamp current). Perhaps the simplestthing to do would be to connect aswitch between the base and collectorwires of the transistor like this:wires of the transistor like this:

Transistor as A SwitchIf the switch is open, the base wire of the transistorwill be left “floating" (not connected to anything) andthere will be no current through it In this state thethere will be no current through it. In this state, thetransistor is said to be cutoff. If the switch is closed,however, electrons will be able to flow from theemitter through to the base of the transistor throughemitter through to the base of the transistor, throughthe switch and up to the left side of the lamp, backto the positive side of the battery. This base currentwill enable a much larger flow of electrons from thewill enable a much larger flow of electrons from theemitter through to the collector, thus lighting up thelamp. In this state of maximum circuit current, thetransistor is said to be saturatedtransistor is said to be saturated.

Biasing Transistor

Biasing Transistor

Forward – ForwardForward – ReverseForward – ReverseReverse – Reverse

dReverse - Forward

Biasing Transistor

Forward - Forward

Biasing Transistor

Forward - Reverse

Biasing Transistor

Reverse - Reverse

Biasing Transistor

Reverse - Forward

Essential Characteristics

Output Characteristic

EECECC

RIVVRIRIVRIVcc =⋅−−⋅− 0

C

EECEC

EECECC

RRIVVccI

RIVVccRI⋅−−

=

⋅−−=⋅

EECCCE

C

RIRIVccVatau

⋅−⋅−=

Input Characteristic

RIVRIV =⋅−−⋅− 0

EEBEBB

EEBEBBBB

EEBEBBBB

RIVVI

RIVVRIRIVRIV

⋅−−⋅−−=⋅

=⋅−−⋅− 0

B

EEBEBBB R

I =

Current Ratio Characteristic

CIβ

C

B

C

II

=β

E

C

II

=α

Final CharacteristicsIc

RasioPenguatan Arus

KarakteristikOutputOutput

Ib1

Ib4Ib3

Ib2

Ib Vce

Karakteristik

Ib1

Vb

KarakteristikInput

Vbe