Right, back to transistors. The three standard transistor marking schemes are:
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.
The letters indicate the application area and flavor 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 diodesThe 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) omitted so, for
example, a 2SC733 would be marked C 733.
Examples- 2SA1187, 2SB646, 2SC733.
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 diodeThe 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.
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 (plastic case) TIPL: TI planar power transistor TIS: TI small signal transistor (plastic case) ZT: Ferranti ZTX: FerrantiExamples- ZTX302, TIP31A, MJE3055, TIS43.
Many manufacturers also make custom parts for large volume OEM use. These parts are optimized 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.
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.