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What Is a 2N Transistor?

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  • Written By: G.W. Poulos
  • Edited By: Daniel Lindley
  • Last Modified Date: 12 July 2014
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A 2N transistor is essentially any transistor having three lead wires. The 2N transistor designation is part of the electronic component numbering system created by the Joint Electron Devices Engineering Council (JEDEC). Formed in 1958, the JEDEC worked alongside the National Electrical Manufacturing Association (NEMA) to establish standards, testing methods, designations, and part numbering systems for various electronic components. NEMA dropped the JEDEC’s direct involvement with its programs in 1979; however, the JEDEC continued to operate as a trade and standardization entity for the semiconductor engineering industry.

At the beginning of the transistor industry in the United States, the Electronic Industries Alliance (EIA) and NEMA cooperated in a joint venture to create an independent standardization body to help set parameters for the budding semiconductor industry. The JEDEC was born of that effort and it began its work in designating the various new semiconductor devices and creating a part numbering system that identified some basic aspects of various semiconductor devices. Early in the organization’s life, there were only two true semiconductor devices: diodes and transistors.

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Diodes are created from two sections of semiconductor material fused together, with a wire lead extending from each of the two sections. One of the sections is positively charged and the other is negatively charged. Where these two sections meet is the diode’s junction. A diode’s junction establishes many of its operational characteristics. As diodes have only one junction, they were designated by the JEDEC as single-junction semiconductor devices and were identified with a part number beginning with 1N.

Virtually all transistors at the time the JEDEC began working alongside NEMA were three wire lead devices. Transistors of that time were constructed almost exclusively of three sections of electrically charged semiconductor material fused together. While the electrical charge could be ordered as either positive-negative-positive, called PNP, or negative-positive-negative, called NPN, all transistors of the day had two junctions where the three sections met. Hence, the JEDEC identified transistors as bi-junction semiconductor devices (meaning they have two junctions) and assigned them part numbers beginning with 2N. This is the origin of the 2N transistor.

Since those early days, and around the time of NEMA and the JEDEC’s parting of ways, many new types of transistors were developed. Many of these had more than three wire leads, and some worked on the principles of electromagnetic fields rather than physical junctions. For example, a dual-gate field effect transistor has but one practical polar junction, but four wire leads.

As the diode already uses the 1N designator, it was not available, so the JEDEC changed the meaning of 1N and 2N to refer to two-wire and three-wire devices. It then assigned the 3N designator to the dual-gate field effect transistor, identifying it as having four wire leads. As a direct result of this change, a 2N transistor became a transistor that has three wire leads and may have two internal junctions, depending on the device’s design.

The JEDEC still operates as an independent body that establishes standards for semiconductor devices; however, it is no longer the only creator of semiconductor part numbers, as two other major standardizing systems are now also in use. Japan has created a standard, called the Japanese Industrial Standard (JIS), where transistor part numbers begin with 2S. The European Pro Electron standard (PE) is another major standard in the world for identifying semiconductor components. Under that system, a letter indicates the material the transistor is made of followed by a letter identifying the type of device. For example, BA indicates a silicon diode, BC indicates a silicon general-purpose transistor, and AD indicates a germanium power transistor.

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