The electronics enthusiast is well acquainted with the classics:
- 2N2222
- BC547B
- BFR91
- 1N4148, etc.
But what if you come across salvaged transistors marked “BFY51” or “C733”? What type are they? The first instinct is, of course, to look them up in a (voluminous) transistor directory, but it is often faster to learn how to “read” transistor markings to quickly determine their type and intended application.
Here is the guide…
The three main marking code systems are:
- Joint Electron Device Engineering Council (JEDEC)
- Japanese Industrial Standard (JIS)
- Pro-Electron
1. JEDEC
This coding system follows the format:
[digit] [letter] [serial number] [suffix]
Example: 2N2222A
The letter is always N, the digit equals the number of terminals minus one (2 for transistors, although 4-pin transistors like dual-gate MOSFETs are also coded 2…). Exceptions include 4N and 5N, reserved for optocouplers. More strictly, this digit corresponds to the number of junctions in the circuit. The serial number, ranging from 100 to 9999, does not carry any specific meaning other than an approximate idea of the circuit’s introduction date. The optional suffix indicates the circuit’s gain group (hfe):
- A = Low gain
- B = Medium gain
- C = High gain
If there is no suffix, the gain is unspecified.
2. JIS
This coding system is found on Japanese transistors and follows the format:
[digit] [two letters] [serial number] [suffix]
Example: 2SC1947
As with JEDEC, the digit equals the number of terminals minus one. The letters indicate the circuit’s application field based on 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 Diodes
- SH: UJT – Unijunction
- 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 Diodes
The serial number, ranging from 100 to 9999, does not hold any specific meaning other than indicating an approximate introduction date. The optional suffix signifies that the type is approved by various Japanese organizations.
Note: Since Japanese transistor markings always start with “2S”, these two characters are often omitted on the package. For example, a 2SC733 transistor may be marked simply as C733.
3. Pro-Electron
This coding system follows the format:
[two letters] [one letter] [serial number] [suffix]
Example: BC557B
The first letter indicates the material:
- A = Germanium
- B = Silicon
- C = Gallium Arsenide (GaAs)
- R = Compound Material
It goes without saying that most transistors start with the letter B!
The second letter indicates the circuit’s application field:
- A: Diode, RF
- B: Varicap
- C: Transistor, AF, Low Signal
- D: Transistor, AF, Power
- E: Tunnel Diode
- F: Transistor, HF, Low Signal
- K: Hall Effect Circuit
- L: Transistor, HF, Power
- N: Optocoupler
- P: Radiation-sensitive Circuit
- Q: Radiation-emitting Circuit
- R: Low Power Thyristor
- T: Power Thyristor
- U: Switching Power Transistor
- Y: Rectifier
- Z: Zener Diode, Voltage Regulator Diode
The third letter indicates whether the circuit is intended for industrial or professional use rather than domestic applications. Common letters include W, X, Y, and Z.
The serial number varies from 100 to 9999 and carries no special meaning beyond an approximate introduction date.
The optional suffix indicates the gain group, similar to JEDEC, as in BC108A, BAW68, BF239, BFY51, BC547B, etc.
Except for JEDEC, manufacturers using JIS and Pro-Electron standards often introduce their own types for commercial reasons (e.g., to incorporate their brand name into the circuit reference). Some common brand prefixes include:
- MJ: Motorola, metal-case power transistor
- MJE: Motorola, plastic-case power transistor
- MPS: Motorola, low-power plastic-case transistor
- MRF: Motorola, HF, VHF, and microwave transistors
- TIP: Texas Instruments power transistor, plastic case
- TIPL: Texas Instruments planar power transistor
- TIS: Texas Instruments low-signal plastic-case transistor
- ZT, ZTX: Ferranti
Source: f8kgl.com | CC