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TRANSISTOR

SEBAGAI FUNGSI PENGUAT

(Analisa DC)

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On = saturasi

Off = cut off

AB

C

Gb.1 Kurva karakteristik output transistor CE

ANALISA DC 1

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Current & Voltage Analysis Consider below figure. Three dc currents and three

dc voltages can be identified

IB: dc base current

IE

: dc emitter currentIC: dc collector currentVBE: dc voltage across base-

emitter junctionVCB: dc voltage acrosscollector-base junctionVCE: dc voltage from

collector to emitter

Transistor bias circuit.

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Collector Current (IC)

The ratio of IC to IE is called alpha (), values

typically range from 0.95 to 0.99.

E

C

I

I

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Base Current (IB) IB is very small compared to IC;

The ratio of IC to IB is the dc current gain of a

transistor, called beta ()

The level of beta typically ranges from about

50 to over 400

B

C

I

I

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Current & Voltage Analysis

When the BE junction is forward-biased, it islike a forward-biased diode. Thus; (Si = 0.7, Ge

= 0.3)

From HVK, the voltage across RB is

By Ohms law;

Solving for IB

BEBBR VVV B

BBR RIV B

B

BEBB

BR

VVI

V7.0VBE

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Current & Voltage Analysis The voltage at the collector is;

The voltage drop across RC is

VCE can be rewritten as

The voltage across the reverse-biased CB

junction is

CCR RIV C

CRCCCEVVV

CCCCCERIVV

BECECB VVV

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Transistor as Amplifier

Transistor is capable toamplify AC signal :(output signal > inputsignal)

Eg: Audio amplifier thatamplify the sound of aradio

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Transistor Amplifier Circuit Analysis

There are 2 analysis;

DC Analysis

AC Analysis Transistor will operate when DC voltage

source is applied to the amplifier circuit

Q-point must be determined so that thetransistor will operate in active region (can

operate as an amplifier)

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DC LOAD LINE (Example)

VCC = 8V

RB = 360 k

RC = 2 k

Draw DC Load Line and Find Q-point.

Answers;

mA

k

V

R

VI

CE

sat

VC

CCC 4

2

8

0

0)(

Coff ICCCCCE RIVV

VVV CCCEoff 8)(

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DC LOAD LINE (Example)

Draw DC Load Line and Find Q-point.

Answers;

Q-point can be obtained by

calculate the half values of

maximum IC and VCE

4V

2 mA

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DC Analysis of Amplifier Circuit

Amplifier Circuit Amplifier Circuit w/o capacitor

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DC Analysis of Amplifier Circuit

Amplifier Circuit w/o capacitor Simplified Circuit

Thevenin Theorem;

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DC Analysis of Amplifier Circuit

Important equation for DC Analysis

1

2

21

21

21//

RR

RRRRR

TH

CCTHV

RRRV

21

2

BC

ETH

BETH

B IIRR

VV

I

;)1(

)(ECCCCCE

RRIVV

1

2

From HVK;

From Thevenin Theorem;

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Contoh 1

Hitung Vc dan tentukan garis bebab DC

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Contoh 2

Dengan hfe = 200, tentukan Rb, Vbb, IB, IC,

IE, Vc, VE dan Vc

VCE= VC VE = 5,03 V