Transistors

Transistors may be in plastic or metal can packages. Value of the transistor is printed on its body. Pin numbers are generally assigned as 1,2 and 3 from the facing side.
  

General purpose NPN transistors have pins 1-Collector, 2-Base, 3- Emitter. That is CBE. In PNP types the pins are reversed. 1-Emitter, 2-Base and 3- Collector. That is EBC. Metal can transistors have a small projection in the rim of the body.

The pin close to it is the emitter. Pin opposite to the emitter is Collector and the middle pin is base. Pin assignment of some common transistors is given below.

 

    

Transistor	Type	Pins 1 2 3	Transistor	Type	Pins 1 2 3
BC546,547,548,549 550, BC 337,AC 187	NPN	CBE	2N 2222A,2N 3904	PNP	EBC
TIP 120,121,122	NPN	BCE	TIP 125,126,127	PNP	EBC
BD139	NPN	ECB	BD140	PNP	ECB
BF494,495	NPN	CEB	MPSA 92,42,44	PNP	EBC
C2570	NPN	BEC	BC636	PNP	BCE
C1730	NPN	ECB	SK/CK/BEL100P	PNP	EBC
BD677	NPN	BCE	AC188	PNP	EBC
D882 / 2SD882	NPN	ECB	BC557	PNP	EBC
D313/MJE 13005	NPN	BCE	BC558	PNP	EBC