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Home > Ordnance Documents and other related manuals > > Transistor Theory.
Transistor Fundamentals.
NPN Transistor Operation

Electronic Principles
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ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 2
c. Classification. The two basic types of transistors are the
negative­positive­negative (NPN) and the positive­negative­
positive (PNP). The only difference in symbology between the
two transistors is the direction of the arrow on the emitter.
If the arrow points in, it is a PNP transistor and if it points
outward, it is an NPN transistor.
d. Construction. The four transistor manufacturing processes
are:
(1) Point contact;
(2) Grown or rate­grown junction;
(3) Alloy or fused junction; and
(4) Diffused junction.
Each of these types of manufacture will he discussed briefly in
the following paragraphs.
Point­contact transistors are now practically obsolete. They
have been replaced by junction transistors, which are superior
to point­contact transistors in nearly all respects. The
junction transistor generates less noise, handles more power,
provides higher current and voltage gains, and can be mass­
produced more cheaply than the point­contact transistor.
Junction transistors are manufactured in much the same manner as
the PN­junction diode discussed in paragraph 3i(1)(c) on pages
112 and 113 of this task. However, when the PNP or NPN material
is grown, the impurity mixing process must be reversed twice in
order to obtain the two junctions required in a transistor.
Likewise, when the alloy­junction on or the diffused junction
process is used, two junctions must also be created within the
crystal.
e. Transistor Theory. The proper biasing of a transistor
enables the transistor to be used as an amplifier. To function
in this capacity, the emitter­to­base junction of the transistor
is forward biased, while the base­to­collector junction is
reverse biased.
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