1. Packaging and Terminal Identification of Transistor

3. Packaging of Transistor
2N3055, NPN TO3
BD178, PNP TO126
BC327, PNP TO92
TO-126
TO-92

4. Packaging Approx. power Power range SOT-23 0.3W 0.2-0.5W TO-92 0.5W
Power capability
continuous maximum power 
Packaging
Approx. power
Power range
SOT-23
0.3W W
TO-92
0.5W
0.4-1W
TO-126 (SOT-32)
40W
12.5W-40W
TO-220
80W
40-350W
TO-247
100W
70-370W
TO-3
200W W

6. Instructions
Ensure that the 2N3055 transistor sits so its two legs point down.
Turn the transistor horizontally until one of the mounting holes is nearer to you, and the legs are closer to you than the other mounting hole. The legs are not the same distance from the mounting holes; they are closer to one hole than the other.
Identify the transistor's legs. The left one is the base, the right one is the emitter and the case is the collector.

7.  2N TRANSISTOR, NPN, 15A, 40V, TO220

8. SB1560 – pnp Power TRANSISTOR, 100W, MT 100 (TO3P)C E

9. BJT terminals
pnp or npn transistor
BD178, PNP TO126

12. Transistor Prefix Table
Prefix class
Type and usage
Example AC
Germanium small-signal AF transistor
AC126 AD
Germanium AF power transistor
AD133 AF
Germanium small-signal RF transistor
AF117 AL
Germanium RF power transistor
ALZ10 AS
Germanium switching transistor
ASY28 AU
Germanium power switching transistor
AU103 BC
Silicon, small-signal transistor ("general purpose")
BC548 BD
Silicon, power transistor
BD139 BF
Silicon, RF (high frequency) BJT or FET
BF245 BS
Silicon, switching transistor (BJT or MOSFET)
BS170 BL
Silicon, high frequency, high power (for transmitters)
BLW60 BU
Silicon, high voltage (for CRT horizontal deflection circuits)
BU2520A CF
Gallium Arsenide small-signal Microwave transistor (MESFET) 
CF739 CL
Gallium Arsenide Microwave power transistor (FET)
CLY10