TRANSISTOR CODES
There are three main series of transistor codes used in the UK:
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 denotes the material
B - SILICON
A - GERMANIUM
The second letter denotes the type of the transistor
C-LOW PWER AUDIO FREQUENCY
D-HIGH POWER AUDIO GREQUENCY
F-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 or
maximum 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
Code Structure Case style IC max. VCE max. hFE min. Ptot max. Category (typical use) Possible substitutesBC107 NPN TO18 100mA 45V 110 300mW Audio, low
power BC182 BC547
BC108 NPN TO18 100mA 20V 110 300mW
General
purpose, low
power
BC108C BC183
BC548
BC108C NPN TO18 100mA 20V 420 600mW
General
purpose, low
power
BC109 NPN TO18 200mA 20V 200 300mW
Audio (low
noise),low
power
BC184 BC549
BC182 NPN TO92C 100mA 50V 100 350mW
General
purpose, low
power
BC107 BC182L
BC182L NPN TO92A 100mA 50V 100 350mW
General
purpose, low
power
BC107 BC182
BC547B NPN TO92C 100mA 45V 200 500mW Audio, low
power BC107B
BC548B NPN TO92C 100mA 30V 220 500mW
General
purpose, low
power
BC108B
BC549B NPN TO92C 100mA 30V 240 625mW
Audio (low
noise), low
power
BC109
2N3053 NPN TO39 700mA 40V 50 500mW
General
purpose, low
power
BFY51
BFY51 NPN TO39 1A 30V 40 800mW
General
purpose,
medium power
BC639
BC639 NPN TO92A 1A 80V 40 800mW
General
purpose,
medium power
BFY51
TIP29A NPN TO220 1A 60V 40 30W
General
purpose, high
power
TIP31A NPN TO220 3A 60V 10 40W
General
purpose, high
power
TIP31C TIP41A
TIP31C NPN TO220 3A 100V 10 40W
General
purpose, high
power
TIP31A TIP41A
TIP41A NPN TO220 6A 60V 15 65W
General
purpose, high
power
2N3055 NPN TO3 15A 60V 20 117W
General
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
Code Structure Case
style
IC
max.
VCE
max.
hFE
min.
Ptot
max.
Category
(typical
use)
Possible
substitutes
BC177 PNP TO18 100mA 45V 125 300mW Audio, low
power BC477
BC178 PNP TO18 200mA 25V 120 600mW
General
purpose, low
power
BC478
BC179 PNP TO18 200mA 20V 180 600mW
Audio (low
noise), low
power
BC477 PNP TO18 150mA 80V 125 360mW Audio, low
power BC177
BC478 PNP TO18 150mA 40V 125 360mW
General
purpose, low
power
BC178
TIP32A PNP TO220 3A 60V 25 40W
General
purpose, high
power
TIP32C
TIP32C PNP TO220 3A 100V 10 40W
General
purpose, high
power
TIP32A
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.
Structure This 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.
http://www.kpsec.freeuk.com/components/tran.htm (7 of 9)11/25/2008 8:03:29 PM
Transistors
hFE This 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.
Category This 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 substitutes These 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.
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