Discussion: Schematic designators: T vs Q (also U vs IC) - Page 1
Forum section: electronics / general

author: RedLion
author_rank: Regular Contributor
timestamp: July 13, 2021, 08:52:32 pm
content: So, in most schematics, transistors are usually designated by Q**, but I see more and more schematics and libraries using T**, especially in Europe or with younger engineers.Same goes for integrated circuits, using IC** in favor of U**.I personally adopted the T** and IC** designators since University, before that I just followed the default Altium library.I wondered, is either one the "correct" way? I don't think there is a broadly accepted standard on this. Also, what do you guys use? Are there any regional differences?

author: jpanhalt
author_rank: Super Contributor
timestamp: July 13, 2021, 09:00:42 pm
content: Usually, it is pretty easy to answer such questions. Either the program you are using will give a clue or Google, or god forbid:https://en.wikipedia.org/wiki/Reference_designator

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2021, 09:06:56 pm
content: That wikipedia article agrees with my traditional US usage:Q for transistor, vs. T for transformerU for integrated circuit, vs. V for vacuum tube,etc.

author: RedLion
author_rank: Regular Contributor
timestamp: July 14, 2021, 12:49:30 am
content: Quote from: jpanhalt on July 13, 2021, 09:00:42 pmWell that's what I'm wondering, I use Altium, which is famously Australian, so the (admittedly useless) preinstalled library uses Q and U, but in Germany I see IC and T more often. I took it up since my bachelor's thesis, where I had to work with the institute's library, and have been since then, also because I "stole" a few footprints for myself. I also prefer T for transistors since I use way more of those than transformers.There is the DIN/EN-norm 81346 I found, but it's really strange and no-one uses it; it defines the function of a part rather than the part itself, so for example Q is defined as "controlled switching or varying of a flow of energy, signal or matter". Certainly an easy to grasp conceptAlso are these norms not a bit of a mute point anyway, since the designator is usually next to the symbol so you'd know anyway?

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 14, 2021, 09:15:39 pm
content: The list in the Wikipedia article looks reasonable to me.There are a few minor things that I do not exactly follow (and that are frequently not exactly followed.) For instance, I use "X" for crystals or oscillators, but apparently X would be a socket, and Y should be used instead (or XTAL for crystals only.) "X" is very common for that though. Also, "J" apparently should be used only for jack-like connectors, but I use it for all kinds of connectors including headers...

author: TimFox
author_rank: Super Contributor
timestamp: July 14, 2021, 09:25:02 pm
content: I also prefer "X" for crystals, "J" for female connectors, and "P" for male connectors, but that doesn't work in other languages. I believe "S" for "Stecker" is used in German for a male plug.The older standard prefix for a solid-state diode was "CR", which stood for "crystal rectifier".

author: Feynman
author_rank: Regular Contributor
timestamp: July 14, 2021, 09:33:05 pm
content: I often see "V" for transistors, as well.

author: Cerebus
author_rank: Super Contributor
timestamp: July 14, 2021, 09:39:29 pm
content: Quote from: jpanhalt on July 13, 2021, 09:00:42 pmAnd all of the documents that references areAmericanstandards of one flavour or another (IEEE, ANSI, ASME). T or TR designators for transistors and IC for integrated circuits was common European practice and is no doubt called out as such in some DIN, EN, ISO or IEC standard of some vintage.There is no "correct" scheme, unless you are locally required to work to some particular designated standards document because you're doing government or military work or because some particular customer insists. Use whatever scheme you're most comfortable with and if there's any doubt about making your intentions clear to others in a schematic, just put a small "key" block somewhere.

author: TimFox
author_rank: Super Contributor
timestamp: July 14, 2021, 09:42:50 pm
content: Quote from: Feynman on July 14, 2021, 09:33:05 pmI see that in older drawings, since "V" denoted "tube" in American practice (probably from "valve" in British practice).Using literal initials is an obvious problem with different languages.

author: RedLion
author_rank: Regular Contributor
timestamp: July 14, 2021, 09:57:49 pm
content: I much prefer the clarity of T and IC over Q and U.What do these stand for anyway?

author: TimFox
author_rank: Super Contributor
timestamp: July 14, 2021, 10:56:19 pm
content: My guess is "U" for "unit", but I never saw an origin for "Q". "CR" for diode lasted a long time. Perhaps "Q" comes from your DIN definition of its function?"T" may be clear for transistor, but what, then, should we call a transformer?

author: RedLion
author_rank: Regular Contributor
timestamp: July 14, 2021, 11:02:27 pm
content: Quote from: TimFox on July 14, 2021, 10:56:19 pmNo, I don't think so, that norm is quite recent.Quote from: TimFox on July 14, 2021, 10:56:19 pmWe use TR for transformer. Not better on the confusion bit, but well, whadyagonnado?I've seen TF somewhere as well, not sure how I feel about that.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 14, 2021, 11:47:25 pm
content: The use of U for integrated circuits comes from the ASME/IEEE standard where U is used for an "inseparable unit". Logical but not the easiest thing to remember.It doesn't seem that component designators have ever been important enough for force international standardization. When the designator is next to the symbol (which is slightly more standardized worldwide) it is obvious enough, and in a stand alone parts list the part number identifies the part well enough that knowing its category isn't too important. The only time I have really found much use for the designator is in sorting parts lists, and for that purpose consistency within the list is all that is necessary. It really would be awkward using multiple designators in a single schematic.