# Prepared by: Cesar Mendoza

Ηλεκτρονική - Συσκευές

2 Νοε 2013 (πριν από 4 χρόνια και 8 μήνες)

93 εμφανίσεις

Prepared by: Cesar Mendoza

Applied Technology Teacher

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

Upon successful completion of this module, students should be able to:

1.
State the advantages of a transistor over vacuum tubes.

2.
Define a Bipolar Junction Transistor.

3.
Differentiate between an NPN and a PNP transistor in terms of their
construction, two
-
diode analogy and symbols.

4.
Identify the three different BJT terminals and state the function of each
terminal.

5.
Recognize the low
-
power and high
-
power BJTs.

6.
Measure transistor currents, and confirm that the emitter current is the sum of
the collector and base currents.

7.
State the common applications of a Bipolar Junction Transistor.

8.
Describe the three different BJT configurations with the help of circuit
diagrams.

9.
Describe the application of a BJT as a switch through a practical
demonstration.

10.
Build and test an ‘automatic night lamp circuit’ to demonstrate the function of
a BJT as a switch.

11.
Build and test a simple temperature control system.

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

The reasons are obviously its
such as :

1.
compact size,

2.
light weight,

3.
more resistive to shocks and vibrations,

4.
low operating voltage,

5.
long life and so on.

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

A
B
ipolar
J
unction
T
ransistor (
BJT
) is defined as a
three
-
terminal semiconductor device, whose
operation depends upon the flow of electric charge
carriers within the solid.

The word
transistor

is derived from the combination of two
words, “Transfer
-
Resistance”. It means that it is a device,
which transfers a low resistance into a circuit having high
resistance.

Transistors in general are classified as bipolar or
unipolar

type. The bipolar type has two PN
-
Junctions, while
unipolar

types have only one PN
-
Junction.

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

The three regions are called

1.
Emitter (E),

2.
Base (B), and

3.
Collector (C),

and the two PN
-
junctions are

a.
C
-
B junction and

b.
E
-
B junction
.

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

E

E
-

Emitter

C
-

Collector

Base
-
B

Emitter:

To emit majority charge
carriers into the base.

Base:

Base is the middle, extremely
thin, and lightly doped region. It
controls the electrons flowing to the
collector.

Collector:

To collect the emitted
charge carriers through the base.

The functions of the three regions
are as follows:

Low

power
, small
-
signal transistors are sealed in a metal, plastic or
epoxy package.

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

High power

transistors are usually designed to be
mounted onto a metal frame, which acts as a heat sink
(to conduct heat away).

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

To use a BJT, we connect it so that:

A.
Its emitter is its negative terminal.

B.
The collector is several volts positive
of its emitter.

C.
The base is 0.7V (or slightly more)
positive of its emitter.

Under these conditions, we find that:

1.
A small base current flows into the base.

2.
A much larger current flows into the
collector.

3.
The base and collector currents flow out
of the emitter

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

I
E

= I
C

+ I
B

where I
E

Emitter current, I
C

Collector current, and
I
B

Base current

Common applications of a transistor include the following:

1.
A switch

2.
An amplifier

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

When the switch is closed,

a small current flows into the
base (B) of the transistor,
which is just enough to make
LED B glow dimly.

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

When the switch is open
,

no base
current flows, so the transistor
switches off the collector current.

Amplification is the process of increasing the level of a weak signal. A
small change in the base current of a transistor produces a large variation
in the collector current

Prepared by: CESAR MENDOZA
-
Applied Technology Teacher

Prepared by: CESAR MENDOZA
-
Applied Technology
Teacher

Prepared by: CESAR MENDOZA
-
Applied Technology
Teacher

Prepared by: CESAR MENDOZA
-
Applied Technology
Teacher