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TM 9-254
7-7. Semiconductor Identification - Continued
a. Transistors. Transistors are now found in almost every type of electronic circuit Although they come in many
sizes and serve many functions, the two most common types encountered are the N-P-N and the P-N-P. The
schematic diagrams for these transistors are found in figure 7-15. Standard convention is for the arrow in the
schematic to point toward the N type material.
N-P-N
P-N-P
Figure 7-15. N-P-N and P-N-P Transistors
(1)
Transistors are marked with a 2N which identifies the part as a transistor followed by a series of numbers which
identify the type of transistor. This number is found on the top or side of the transistor package. Transistors are
packaged in a wide variety of different containers. The most common packaging encountered is the three lead,
can-like package shown in figure 7-16.
Figure 7-16. Transistor Packaging
(1)
Typically the emitter (E) is the lead closest to the tab on the transistor as shown in figure 7-16. The base (B) and
collector (C) are found by going clockwise from the emitter while looking at the bottom of the transistor.
NOTE
These are typical connections most commonly found. A transistor data book
which provides drawings of connection layout should be used to verify the proper
connections for a specific type of transistor.
a. Dual-In-Line Packages (DIPs). These components are rectangular, integrated circuit components with leads usually
mounted through the board Dimensions and numbers of leads vary. Index or orientation markings appear in the center of
one short side of the component body, while lead numbers appear on top of the component and are read in a
counterclockwise direction.
Change 6 7-15
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