Most transistor markings follow one of these codes: JEDEC, JIS or Pro-Electron. For ICs, look for known
These part numbers take the form: digit, letter, sequential number, [suffix]
The letter is always 'N', and the first digit is 1 for diodes, 2 for transistors, 3 for four-leaded devices, and so forth. But 4N and 5N are reserved for opto-couplers. The sequential numbers run from 100 to 9999 and indicate the approximate time the device was first made.
If present, a suffix could indicate various things. For example, a 2N2222A is an enhanced version of a 2N2222. It has higher gain, frequency, and voltage ratings. Always check the data sheet.
Examples: 1N914 (diode), 2N2222, 2N2222A, 2N904 (transistors).
NOTE: When a metal-can version of a JEDEC transistor is remade in a plastic package, it is often given a number such as PN2222A which is a 2N2222A in a plastic case.
2. Japanese Industrial Standard (JIS)
These part numbers take the form: digit, two letters, sequential number, [optional suffix]
Digits are 1 for diodes, 2 for transistors, and so forth. The letters indicate the type and intended application of the device according to the following code:
SA: PNP HF transistor
SC: NPN HF transistor
SG: Gunn devices
SJ: P-channel FET
ST: Avalanche diodes
SZ: Zener diodes
SB: PNP AF transistor
SD: NPN AF transistor
SK: N-channel FET
SS: Signal diodes
The sequential numbers run from 10-9999. The optional suffix indicates that the type is approved for use by various Japanese organizations. Since the code for transistors always begins with 2S, it is sometimes omitted; for example, a 2SC733 could be marked C733.
Examples: 2SA1187, 2SB646, 2SC733.
3. Pro-Electron (European)
These part numbers take the form: two letters, [letter], sequential number, [suffix]
The first letter indicates the material:
A = Ge
B = Si
C = GaAs
R = compound materials.
The second letter indicates the device type and intended application:
A: diode, RF
C: transistor, AF, small signal
D: transistor, AF, power
E: Tunnel diode
F: transistor, HF, small signal
K: Hall effect device
L: Transistor, HF, power
P: Radiation sensitive device
Q: Radiation producing device
R: Thyristor, Low power
T: Thyristor, Power
U: Transistor, power, switching
Z: Zener, or voltage regulator diode
The third letter indicates if the device is intended for industrial or commercial applications. It's usually a W, X, Y, or Z. The sequential numbers run from 100-9999.
Examples: BC108A, BAW68, BF239, BFY51.
Instead of 2N and so forth, some manufacturers use their own system of designations. Some common prefixes are:
MJ: Motorola power, metal case
MJE: Motorola power, plastic case
MPS: Motorola low power, plastic case
MRF: Motorola HF, VHF and microwave transistor
RCA: RCA device
TIP: Texas Instruments (TI) power transistor, plastic case
TIPL: TI planar power transistor
TIS: TI small signal transistor (plastic case)
Examples: ZTX302, TIP31A, MJE3055.
Many manufacturers also make custom parts, or custom-label standard parts, for large volume OEM customers. Typically, they have the OEM's mark or logo and part-number. When such parts hit the surplus market, they end up in hobbyist "bargain packs". Since data on these devices is not usually available, they are best used as LED-drivers and other such applications where the actual specifications are not critical.