Note from Writer: There is an information gap concerning the written standard used at AT&T and Western Electric during this time. If you or a loved one have a copy of the specific internal standard that AT&T used to designate vacuum tubes in the late 1940s to early 1950s, please get in touch with technical.content@digikey. com with the subject line ‘Retro Electro’ with information. Thank you.
numbers for diodes, transistors, and optoelectronic devices. It is important to know that this system was never intended for Integrated Circuit devices. The current standard is available on the JEDEC website for free download.
It is important to recognize that 1Nxxxx and 2Nxxxx part numbers are not related, meaning a 1N2222 and a 2N2222 have no inherent characteristics in common other than being discrete semiconductor devices. The reader may ask, why is it ‘n minus one’ and why not just the number of pins? Consider that the ordinary farm-grown diode, which can be purchased from Digikey, has two connections: the anode and the cathode. There will never be a single- pin semiconductor device to start numbering with ‘1’. The second character can be either a ‘C’ or an ‘N’. Introduced in 1982 with the EIA-370B, the character ‘C’ is used for unencapsulated dies, while the character ‘N’ is used when a die is encapsulated in a registered package. So, the ‘2C2222’ would describe the bare die that would otherwise be used inside a 2N2222 transistor.
How does the EIA-370 work?
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The reader knows part numbers like the 1N4001 and the 2N2222A. Notice that they consist of three or four sets of characters. The 2N2222A transistor is an excellent example of how the EIA-370 numbering system works. Part numbers consist of four groups of characters. The first character is the number of useful connections (‘n’) minus one. Since the 2N2222A is a transistor with three connections, the first character is ‘2’. For parts with more than five useful connections, the character ‘4’ is used. This wasn’t the case for vacuum tubes. Instead, this number would tell the user the voltage of the filament used or the power rating of the tube.
The designation system for discrete semiconductor devices EIA RS-370 By the 1970s, JEDEC (formally JETEC) was maintaining the registration of new designs. The naming convention used by Western Electric twenty years earlier became formalized in 1975 by the publication of the Electronic Industries Association Recommended Standard RS- 370: Designation System for Discrete* Semiconductor Devices (* as distinguished from microelectronic devices). The RS-370 governs the part
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