Transistor codes

Transistor codes

There are three main series of transistor codes used in the UK:
  • Codes beginning with B (or A), for example BC108, BC478
    The first letter B is for silicon, A is for germanium (rarely used now). The second letter indicates the type; for example C means low power audio frequency; D means high power audio frequency; F means low power high frequency. The rest of the code identifies the particular transistor.There is no obvious logic to the numbering system. Sometimes a letter is added to the end (eg BC108C) to identify a special version of the main type, for example a higher current gain or a different case style. If a project specifies a higher gain version (BC108C) it must be used, but if the general code is given (BC108) any transistor with that code is suitable.
  • Codes beginning with TIP, for example TIP31A
    TIP refers to the manufacturer: Texas Instruments Power transistor. The letter at the end identifies versions with different voltage ratings.
  • Codes beginning with 2N, for example 2N3053
    The initial '2N' identifies the part as a transistor and the rest of the code identifies the particular transistor. There is no obvious logic to the numbering system.

Choosing a transistor

Most projects will specify a particular transistor, but if necessary you can usually substitute an equivalent transistor from the wide range available. The most important properties to look for are the maximum collector current IC and the current gain hFE. To make selection easier most suppliers group their transistors in categories determined either by their typical use ormaximum power rating.
To make a final choice you will need to consult the tables of technical data which are normally provided in catalogues.
They contain a great deal of useful information but they can be difficult to understand if you are not familiar with the abbreviations used. The table below shows the most important technical data for some popular transistors, tables in catalogues and reference books will usually show additional information but this is unlikely to be useful unless you are experienced. The quantities shown in the table are explained below.

NPN transistors

CodeCase
style
IC
max.
VCE
max.
V
hFE
min.
Ptot
max.
Category
(typical use)
Possible
substitutes
BC107TO18100mA45110300mWAudio, low powerBC182 BC547
BC108TO18100mA20110300mWGeneral purpose, low powerBC108C BC183 BC548
BC108CTO18100mA20420600mWGeneral purpose, low power 
BC109TO18200mA20200300mWAudio (low noise), low powerBC184 BC549
BC182TO92C100mA50100350mWGeneral purpose, low powerBC107 BC182L
BC182LTO92A100mA50100350mWGeneral purpose, low powerBC107 BC182
BC547BTO92C100mA45200500mWAudio, low powerBC107B
BC548BTO92C100mA30220500mWGeneral purpose, low powerBC108B
BC549BTO92C100mA30240625mWAudio (low noise), low powerBC109
2N3053TO39700mA4050500mWGeneral purpose, low powerBFY51
BFY51TO391A3040800mWGeneral purpose, medium powerBC639
BC639TO92A1A8040800mWGeneral purpose, medium powerBFY51
TIP29ATO2201A604030WGeneral purpose, high power 
TIP31ATO2203A601040WGeneral purpose, high powerTIP31C TIP41A
TIP31CTO2203A1001040WGeneral purpose, high powerTIP31A TIP41A
TIP41ATO2206A601565WGeneral purpose, high power 
2N3055TO315A6020117WGeneral purpose, high power 
Please note: the data in this table was compiled from several sources which are not entirely consistent! Most of the discrepancies are minor, but please consult information from your supplier if you require precise data.

PNP transistors

CodeCase
style
IC
max.
VCE
max.
V
hFE
min.
Ptot
max.
Category
(typical use)
Possible
substitutes
BC177TO18100mA45125300mWAudio, low powerBC477
BC178TO18200mA25120600mWGeneral purpose,low powerBC478
BC179TO18200mA20180600mWAudio (low noise), low power 
BC477TO18150mA80125360mWAudio, low powerBC177
BC478TO18150mA40125360mWGeneral purpose,low powerBC178
TIP32ATO2203A602540WGeneral purpose,high powerTIP32C
TIP32CTO2203A1001040WGeneral purpose,high powerTIP32A
Please note: the data in this table was compiled from several sources which are not entirely consistent! Most of the discrepancies are minor, but please consult information from your supplier if you require precise data.
StructureThis shows the type of transistor, NPN or PNP. The polarities of the two types are different, so if you are looking for a substitute it must be the same type.
Case style.There is a diagram showing the leads for some of the most common case styles in the Connecting section above. This information is also available in suppliers' catalogues.
IC max
Maximum collector current.
VCE max.Maximum voltage across the collector-emitter junction.
You can ignore this rating in low voltage circuits.
hFEThis is the current gain (strictly the DC current gain). The guaranteed minimum value is given because the actual value varies from transistor to transistor - even for those of the same type! Note that current gain is just a number so it has no units.
The gain is often quoted at a particular collector current IC which is usually in the middle of the transistor's range, for example '100@20mA' means the gain is at least 100 at 20mA. Sometimes minimum and maximum values are given. Since the gain is roughly constant for various currents but it varies from transistor to transistor this detail is only really of interest to experts.
Why hFE? It is one of a whole series of parameters for transistors, each with their own symbol. There are too many to explain here.
Ptot max.Maximum total power which can be developed in the transistor, note that a heat sink will be required to achieve the maximum rating. This rating is important for transistors operating as amplifiers; the power is roughly IC × VCE. For transistors operating as switches the maximum collector current (IC max.) is more important.
CategoryThis shows the typical use for the transistor, it is a good starting point when looking for a substitute. Catalogues may have separate tables for different categories.
Possible substitutesThese are transistors with similar electrical properties which will be suitable substitutes in most circuits. However, they may have a different case style so you will need to take care when placing them on the circuit board.

0 comments:

Post a Comment

Read Quran

English Learning