chapter 3: islamic university of gaza bipolar junction...

Chapter 3:

Bipolar Junction Transistors

Islamic University of Gaza

Dr. Talal Skaik

Copyright ©2009 by Pearson Education, Inc.

Upper Saddle River, New Jersey 07458 • All rights reserved.

Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

Common–Emitter Configuration

•The emitter is common to both input (base-emitter) and output (collector-

emitter).

•The input is on the base and the output is on the collector.

2 Dr. Talal Skaik 2014




Common-Emitter Characteristics


(a) collector characteristics; (b) base characteristics.




Common-Emitter Amplifier Currents

IC = IE + ICBO

When IB = 0 A the transistor is in cutoff, but there is some

minority current flowing called ICEO.

B

B

1 1

I =0, and take 0.996,

(0 A)250

1 1 0.996 1 0.996 0.004

If were 1 A, the resulting collector current with I =0 A would

be 250(1 A) =0.25 mA, as reflect

CBOBC

CBO CBO CBOC CBO

CBO

III

For

I I II I

I

ed in the characterestics.

where ICBO = minority collector current

4

ICBO is usually so small that it can be ignored, except in high

power transistors and in high temperature environments.

Dr. Talal Skaik 2014

Since IE = IC + IB , IC = (IC + IB ) + ICBO

0 μA1 B

CBOCEO I

II

α




Beta ()

In DC mode:

In AC mode:

represents the amplification factor of a transistor. ( is sometimes

referred to as hfe, a term used in transistor modeling calculations)

B

C

I

Iβ dc

constantac

CEVB

C

I

I


For practical devices is typically 50 to over 400.




Determining from a Graph

Beta ()

108

A 25

mA 2.7β 7.5VDC CE

100

μA 10

mA 1

μA) 20 μA (30

mA) 2.2mA (3.2β

7.5V

AC

CE

6

ac and dc are usually reasonably close and are often used

interchangeably.





Relationship between amplification factors and :-

1β

βα

1α

αβ

Beta ()

Relationship Between Currents

BC βII BE 1)I(βI

7

using ,

1 1 1

( 1)

C C

B E

E C B

C CC

I I

I I

and I I I

I II

, = ,E C B B BI I I I I





Biasing


Determining the proper biasing arrangement for a common-emitter

npn transistor configuration.




Common–Collector Configuration The input is on the base and the output is on the emitter.





Common–Collector Configuration The characteristics are similar to those of the common-emitter

configuration, except the vertical axis is IE.





Transistor Testing

• DMM

Some DMMs measure DC or hFE.

• Ohmmeter

11

Checking the forward-biased base-to-

emitter junction of an npn transistor.

Checking the reverse-biased base-to-

collector junction of an npn transistor.





12

Various types of general-purpose or switching transistors:

(a) low power; (b) medium power; (c) medium to high power.


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