Pro Electron - Semiconductor Diodes and Transistors

Semiconductor Diodes and Transistors

As listed above, he first letter gives the semiconductor type; the second letter denotes the intended use:

2nd letter Usage Example
A Low power/small signal diode AA119, BA121
B Varicap diode BB105G
C Small signal transistor, RthG > 15K/W BC546C
D High power, low frequency power transistor, RthG ≤ 15K/W BD139
E Tunnel (Esaki-)diode AE100
F Low power, RF (high frequency) Bipolar or FET, RthG > 15K/W BF245
G Hybrid device BGY32, BGY585
H Hall effect sensor/diode
L High frequency, high power transistor (for transmitters), RthG ≤ 15K/W BLW34
M Ring modulator-type frequency mixer
N Opto-isolator CNY17
Q Radiation generator (LED) CQY99
R Low-power control or switching device: Thyristors, Diacs, Triacs, UJTs, Programmable uni-junction transistors (PUT), Silicon bidirectional switch (SBS), Opto-triacs etc. BR100
S Low-power switching transistor, bipolar or MOSFET, RthG > 15K/W BS170
T High-power control or switching device: Thyristors, TRIACs, Silicon bidirectional switch (SBS), etc. BT138
U High-power switching transistors, bipolar or MOSFET, RthG ≤ 15K/W BU508, BUZ11
V Antenna
W Surface acoustic wave device
X Frequency multiplier: Varactor, Step recovery diode
Y High-power rectifying diode BY228
Z Avalanche, TVS, Zener diode BZY91

A 3-digit sequence number (or one letter then 2 digits, for industrial types) follows. Examples are:

Prefix class Usage Example
AC Germanium small signal transistor AC126
AF Germanium RF transistor AF117
BC Silicon, small signal transistor ("allround") BC548B
BD Silicon, power transistor BD139
BF Silicon, RF (high frequency) BJT or FET BF245
BS Silicon, switching transistor Bipolar or MOSFET) BS170
BL Silicon, high frequency, high power (for transmitters) BLW34
BU Silicon, high voltage (for CRT horizontal deflection circuits) BU508

With early devices, the number indicated the case type. Suffixes may be used, such as a letter (e.g. "C" often means high hFE, such as in: BC549C). Other codes may follow to show gain (e.g. BC327-25) or voltage rating (e.g. BUK854-800A). A BC546 might only be marked "C546", thus possibly creating confusion with JIS abbreviated markings, because a transistor marked "C546" might also be a 2SC546.

  • Short summary of semiconductor diode and transistor designations
BC549C / \ \ \___ variant (A,B,C for transistors implies low, medium or high gain) / \ \____ serial number (3 digits or letter and 2 digits) / \_____ device type: A=Germanium A=Signal Diode B=Silicon C=LF Low Power transistor C=GaAs D=Power transistor F=RF transistor (or FET) P=Photosensitive transistor T=Triac or Thyristor Y=Rectifier Diode Z=Zener diode

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