Transistor History

An Introduction To The Transistor History

An Introduction To The Transistor History

Invented in 1948 at the bell telephone laboratories in the usa. the transistor is a semiconductor amplifying device which has largely replaced the valve 'thermionic tube' in electronics.

there are several fundamentally different types of 'tran-sistors',but to most people a transistor is of the 'bipolar junction' type. this is a three-lead device with special names for its terminals input = 'base',output = 'collector' and common = 'emitter'.this compendium confines itself mainly to such transistors with only a few passing references to special 'non-transistor' three terminal devices such as fet's unipolar or field effect transistors, phototransistors, thy-ristors scr's , etc.

When you are considering a transistor type, the first thing is to confirm it is a junction type, and not for example an un-obtainable early'point contact' type or an fet.

Next you must identify whether it is 'NPN' using positive supply rail or 'PNP' using negative supply. Any replacement must be of the same polarity, i.e. NPN or PNP.

Two semiconductor materials, germanium and silicon, are both in common use in transistor manufacture, although silicon is steadily replacing germanium. Leakage currents in germanium devices are orders of magnitude higher than in silicon. As a result, it is prudent normally to replace german-ium with germanium and silicon with silicon.
However, skilled engineers can usually select a silicon low leakage device to substitute for an unobtainable germanium high leakage one. This does not usually work the other way round.

Many differently shaped cases have been developed over the years for transistors, and you will need to know details of the case outline in any transistor you are going to use. This compcndium provides such details together with lead/terminal identification diagrams.

The transistor is basically a low voltage device and it is important to check the permissible maximum voltages that can be applied to the various device terminals.This compend-ium gves ratings for collector-base, collector-emitter and emitter -base. the emitter-base rating, often overlooked in transistor listings, is important. In modern silicon transistors it is usually under 6v, whereas the older germanium types were much higher. Also,the higher the frequency-handling cap-ability of the transistor, the lower the emitter voltage rating tends to be.
Thermionic tubes had one big advantage over transistors. They could withstand substantial current overloads 'going blue' without catastrophic results. Transistors unfortunately are catastrophically sensitive to current overloads. It is important, therefore, to know the maximum permissible collector current and ensure it is not exceeded under any circumstances.
The transistor is not so sensitive to heat overloads as to voltage or current. The junction heats up inside the transistor under load and manufacturers carefully specify maximum permissible junction temperature to guard against excessive degradation of device characteristics with time. permissible maximum junction temperature for germanium lie in the region of 60-100'C and for silicon 125-200'C. This is useful in distinguishing silicon from germanium transistors.
For power dissipation, manufacturers specify either a 'free air rating at 25'C for low power devices normally mounted by their leads only, or a'case-rated' dissipation at 25'C case temperature for high power devices usually mounted on some form of fin or heat sink. Occasionally, however, the maximum dissipation is specified as attached to a heat sink at 25'C ambient temperature. It is important to realise that the per-missible dissipation in use must be reduced, i.e. the device 'derated',as the ambient temperature
rises above 25'C. For a device rated p tot at 25'C and with a maximum permissible junction temperature of T, the permissible dissipation at an elevated ambient temperature of T, can be shown to be P!TOT = P tot T,-T, T-25.
One of the most important characteristics of the transistor is its'current gain' also known as'beta' Hfe, i.e. the ratio of the output (collector) current to the input (base) current. It is necessary to know the current gain not only to design the dc bias networks for the device but to compute the stage gain or amplification. Tranisitor beta changes rapidly with the level of standing collector bias current, but is relatively in-sensitive tostanding bias voltage. This compendium therefore quotes the bias current at which the gain is measured.
Finally the high frequency characteristics of the device are important. the two that give the greatest measure of useful information are ft (the frequency at which the current gain falls to unity) and Cob (the collector-to-base capacitance). Generally any replacement should be a device with sim ilar ft and Cob. For silicon it will be found that ft tends to be 10 to 100 times higher than germanium.
The compendium tables give general application guidance on the use of each transistor by a special coding in a separate column.
Additionally the tables offer in the last two columns possible UK and USA substitute standard devices. Substitution guid-ance given should be used with caution because special characteristics not recorded may make the suggested sub-stitute unacceptable in some applications. You should get detailed specification of the proposed substitute from the manufacturer and consider them in relation to your own application before committing yourself. The suggested sub-stitutes can be taken only as general guide lines.

Over the years, manufacturers and standards associations have issued somewhere between 50,000 and 100,000 separate transistor type numbers. The vast majority of these were never widely used or are no longer used by de-signers.
Devices either have type numbers peculiar to individual manufacturers or conform to industry standard serial numbering systems (suppliable by more than one manufacturer).
The principal industry standard numbering systems are:(a) '2N' (The EIA in the USA maintains a register of '2N' types familiarly known as 'jedec' types, which have had
world wide acceptance. The most accessible detailed infor-mation on current '2N' types will be found in the 'Transistor Data Book' published annually with a half yearly
supple-ment by derivation and Tabulation Associates Inc (Data) of 32 Lincoln Avenue, Orange New Jersey, USA.
(b)'Proelectron' (The Association Internationale Por Electron in Europe maintains a register of Pro Electron types which have wide acceptance in Europe. All Commercially available devices registered with the Por Electron organisa-tion are listed together with technical data and the names and addresses of suppliers in the annual edition of 'Semei-conductors' published on behalf of pro Electron by Ae. E. kluwer, Santvoortbeeklaan 21-23, 2100, Deurne-Antwerp, Belgium. Transistors in the pro Electron syatem
are registered either under a two letter/three numeral code (e.g. BC107)for consumer devices, or a three letter/two numeral code (e.g.ACY17) for industrial devices. Device numbers starting with 'A' refer to germanium and 'B' to silicon. All second and third letter have applications significance as indicated

(c) '2S'(in japan, the JIS, japanese Industrila Standards, system of transistor numbering is almost universal, there being very few housecode devices.in this system, all
tran-sistor numbers start with '2S'followed by a letter and several numbers (e.g. 2SB364). The letter after the 'S' has signific-ance: A = PNP hf, B = PNP lf, C = NPN hf,
D = NPN lf).
(d) Old standards (A standard now obsolete but still met with is the 'old European' where the transistor was registered as 'OC' of 'OD' followed by two or three numeraals (e.g.OC28). Aformer UK Government standard gradually being phased out is the CV system-E gives a listing of such CV transistors. Many of these in the 7,000 part
of the series will now be found transferred into the new British Standards Institution'BS9000' system. Where items have been so transferred, the 'CV7' part of the number
will have been replaced by 'BS9300C'.Thus the CV7084 could now appear as BS9300C084.)
the transistors selected for inclusion in this compendium are listted in serial numero-alphabetical order in tables im-mediately following this introduction.The tables
are designed as far as possible to be self explanatory. For readers to whom some of the nomenclature is strange there is in Appendix A an explanatory set of notes
supplementing the tabulation. Be-sides detailed comments on the tables-A incor-porates a ready reference chart of the tabular format and a glossary  of terms
used.