Transistor Info. More articles at Lidström Audio

A FAQ on this newsgroup [sci.electronics] 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 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).

    2. These take the form:

    digit, letter, serial number, [suffix]

    The letter is always 'N', and the first digit is one less than the number of legs, (2 for transistors unless they're crippled although I'm not sure about 4 legged transistors maybe they get a 3) except for 4N and 5N which are reserved for optocouplers. 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).

    3. 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 applicatin 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:>

    Överföring avbröts!

    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 organizations.

    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.

    4. 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:      Variac
        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:     Motorolla power, metal case
MJE:    Motorolla power, plastic case
MPS:    Motorolla low power, plastic case
MRF:    Motorolla 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
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 important. Check carefully before buying.