Prepared by: Cesar Mendoza Applied Technology Teacher Prepared
by: CESAR MENDOZA-Applied Technology Teacher
Slide 2
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
Slide 3
The reasons are obviously its advantages over vacuum tubes 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
Slide 4
A Bipolar Junction Transistor (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
Slide 5
Slide 6
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
Slide 7
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:
Slide 8
Lowpower, small-signal transistors are sealed in a metal,
plastic or epoxy package. Prepared by: CESAR MENDOZA-Applied
Technology Teacher
Slide 9
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
Slide 10
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
Slide 11
Common applications of a transistor include the following: 1. A
switch 2. An amplifier Prepared by: CESAR MENDOZA-Applied
Technology Teacher
Slide 12
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.
Slide 13
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