A FAQ on this newsgroup is "I have a transistor marked ..., what type is it?".
In order to help answer these problems I have compiled a description of the
three major transistor marking codes. We are lucky with transistors that,
apart from a few oddities which I'll talk about later, most markings follow
one of these codes. ICs are more tricky as you're often dealing with custom
chips or mask programmed devices with manufacturers individual codes. A quick
hint though: always look for known numbers (eg 741, 723, 6502, 2764) etc
between the suffix and prefix, and beware of the date code.
Right, back to transistors. The three standard transistor marking schemes are:
1. Joint Electron Device Engineering Council (JEDEC).
These take the form:
digit, letter, serial number, [suffix]
where the letter is always 'N'
the first digit is one less than the number of legs, (2 for transistors unless
they're crippled although 4 legged transistors like dual gate mosfets also
get a 2) except for 4N and 5N which are reserved for optocouplers.
More strictly, the number is the number of junctions the device has.
The serial number runs from 100 to 9999 and tell nothing about the transistor
except its approximate time of introduction.
The (optional) suffix indicates the gain (hfe) group of the device:
A = low gain
B = medium gain
C = high gain
No suffix = ungrouped (any gain).
See the data sheet for the actual gain spread and groupings.
The reason for gain grouping is that the low gain devices are fractionally
cheaper than the high gain devices, resulting in savings for high volume
users.
Examples- 2N3819, 2N2221A, 2N904.
2. Japanese Industrial Standard (JIS).
These take the form:
digit, two letters, serial number, [suffix]
Again, the digit is one less than the number of legs.
The letters indicate the application area and flavour of the device according
to the following code:
SA: PNP HF transistor SB: PNP AF transistor
SC: NPN HF transistor SD: NPN AF transistor
SE: Diodes SF: Thyristors
SG: Gunn devices SH: UJT
SJ: P-channel FET/MOSFET SK: N-channel FET/MOSFET
SM: Triac SQ: LED
SR: Rectifier SS: Signal diodes
ST: Avalanche diodes SV: Varicaps
SZ: Zener diodes
The serial number runs from 10-9999.
The (optional) suffix indicates that the type is approved for use by various
Japanese organisations.
NOTE. since the code for transistors always begins with 2S, it is sometimes
(more often than not is seems) ommitted so, for example, a 2SC733 would be
marked C 733.
Examples- 2SA1187, 2SB646, 2SC733.
3. Pro-electron.
These take the form:
two letters, [letter], serial number, [suffix]
The first letter indicates the material:
A = Ge
B = Si
C = GaAs
R = compound materials.
Needless to say the biggest majority of transistors begin with a B.
The second letter indicates the device application:
A: Diode, RF
B: Varicap
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
N: Optocoupler
P: Radiation sensitive device
Q: Radiation producing device
R: Thyristor, Low power
T: Thyristor, Power
U: Transistor, power, switching
Y: Rectifier
Z: Zener, or voltage regulator diode
The third letter indicates that the device is intended for industrial or
professional rather than commercial applications. It is usually a W,X,Y or Z.
The serial number runs from 100-9999.
The suffix indicates the gain grouping, as for JEDEC.
Examples- BC108A, BAW68, BF239, BFY51.
Apart from JEDEC, JIS and Pro-electron, manufacturers often introduce their
own types, for commercial reasons (ie to get their name into the code) or to
emphasise that the range belongs to a specialist application. Common brand
specific 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
RCS: RCS
TIP: Texas Instruments power transistor (platic case)
TIPL: TI planar power transistor
TIS: TI small signal transistor (plastic case)
ZT: Ferranti
ZTX: Ferranti, the ZTX300 and ZTX600 series are optimised for switching
Examples- ZTX302, TIP31A, MJE3055, TIS43.
Many manufacturers also make custom parts for large volume OEM use. These
parts are optimised for use in a given part of a given circuit. They usually
just have a manufacturers stamp and an untraceable number. Often when a
company goes bankrupt, or has surplus at the end of a production run, these
transistors find their way into hobbyist bargain packs. There is no way that
you can trace data on these devices, so they are only suitable as LED drivers,
buffers, etc, where the actual parameters are not too important. Check
carefully before buying.
Once you have identified your part, a trip to the data sheet or equivalents
book is called for (anyone know of an on-line equivalents list?).
Well good luck.
Mark
