By Kim Lewis
Updated Mar 24, 2022
Transistors are the backbone of modern electronics, serving as switches and amplifiers in circuits. Common materials include silicon and germanium, and the most widely used type is the bipolar junction transistor. Identifying a transistor at a glance is possible thanks to the labeling system stamped on its body.
Transistor markings follow established industry standards: JIS (Japanese Industrial Standard), Pro Electron (European), and JEDEC (North American, now global). While some manufacturers add proprietary tags, understanding these three core systems and having their code charts handy will let you decode virtually any transistor you encounter.
The JEDEC format typically consists of a digit, a letter, and a serial number. The first digit represents the number of leads minus one—so a standard bipolar transistor, which has three leads, starts with “2”. The letter “N” indicates a semiconductor. The remaining alphanumeric sequence (e.g., 2N2222) provides details about the device’s electrical characteristics, which you can confirm in the datasheet or the component’s packaging. Manufacturer identifiers such as “M” for Motorola or “TI” for Texas Instruments may also appear.
Pro Electron labels follow a two‑letter prefix followed by a serial number. The first letter denotes the semiconductor material: “A” for germanium, “B” for silicon. The second letter specifies the transistor type: “C” for small‑signal devices, “D” for power devices, etc. The serial number then encodes additional performance data.
JIS labels combine a digit, two letters, and a serial number. As with JEDEC, the digit reflects leads minus one. The first letter is “S” for semiconductor, while the second letter identifies the transistor’s function—“A” for high‑frequency PNP, “C” for NPN high‑frequency, etc. Often the “2S” prefix is implied and omitted from the component’s exterior.
The 2N3906 is a classic PNP transistor. Its datasheet confirms suitability for low‑voltage, low‑current applications commonly found in small signal circuits.
The BLX87 is an NPN silicon power transistor, optimized for radio‑frequency environments as outlined in its datasheet.
The 2SB560 (often marked simply as B560) is a PNP transistor tailored for low‑frequency power amplification, as detailed in its datasheet.
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