Capacitor symbol: third lead or a rectangle below - Page 1
Forum section: electronics / beginners

author: golden_labels
author_rank: Super Contributor
timestamp: October 19, 2024, 12:14:10 pm
content: In today’s The Signal Path episode,(1)there is a schematic with a capacitor symbol:What is the rectangle below the capacitor?Is this marking an explicit cathode-case connection?(1)The Signal Path #251: Agilent 50GHz PSA (E4448A) Spectrum Analyzer Teardown, Repair & Experiments

author: Andy Chee
author_rank: Super Contributor
timestamp: October 19, 2024, 12:50:13 pm
content: I'm inclined to think that it's a typesetting error, essentially a graphical publishing error.

author: Gyro
author_rank: Super Contributor
timestamp: October 19, 2024, 12:55:24 pm
content: Yes, it looks like a 'typo' to me. I can't see something as small as a 1uF 35V electrolytic / tantalum having three legs.

author: golden_labels
author_rank: Super Contributor
timestamp: October 19, 2024, 01:51:36 pm
content: Explicit three legs, no. But electrolytic capacitors have a connection between the cathode and the case. Either implicit (through the electrolyte) or with the case being directly connected to the cathode (see this axial capacitor). Hence I’m wondering, if possibly this is what the schematic indicates.

author: Andy Chee
author_rank: Super Contributor
timestamp: October 19, 2024, 02:35:35 pm
content: If the third connection on the schematic is truly intentional, then one would presume that such notation has been used on other schematics of other devices by other manufacturers, particularly if it's a commonly used mass produced component.Otherwise, the application of Occam's razor suggests it's a typo.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 19, 2024, 04:00:55 pm
content: Well, without other context, many things:1. Accident. Seems unlikely to me. More likely in drawings, have seen appnotes with goofy ass lines in them, symbols drawn from primitives rather than a style-consistent drafting library, etc.2. It's a library part (symbol) with multiple pins that need to be connected for ERC reasons, but the footprint is whatever.3. The footprint has multiple pins, numbered differently, or the tool doesn't allow one SCH pin to multiple footprint pins mapping, thus the symbol must as well.3a. ...because it's a multiple placement / alternative footprint3b. ...because it's a multi-pin type (e.g. electrolytic with extra base pin(s), tantalum with polarity compensating footprint, etc.)Tim

author: David Hess
author_rank: Super Contributor
timestamp: October 19, 2024, 09:27:58 pm
content: Sometimes a good schematic will show a line parallel to the capacitor connected to one lead, which indicates that the capacitor needs to be oriented correctly to prevent capacitive coupling to the shielded lead, but in this case I think it was just a drafting error.

author: golden_labels
author_rank: Super Contributor
timestamp: October 20, 2024, 12:57:55 am
content: Thanks for the responses. So I’ll assume it’s indeed just a mistake.(more below)

author: coppercone2
author_rank: Super Contributor
timestamp: October 20, 2024, 01:02:40 am
content: I think they just want a axial capacitor with shield to ground, it makes sense to a amplifierits a RF design if its on signal path and their going to make it specificespecially with a FET input

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: October 20, 2024, 02:04:13 am
content: Quote from: coppercone2 on October 20, 2024, 01:02:40 amI think Tek did this on their 475. The AC coupling capacitor would have three legs: one terminal, the other terminal that also happens to be connected to the case, but also a third one also connected to the case but directly soldered onto the case.Seehttps://www.qservice.tv/N_PICS/PICS_TEK_SPARES/ALL_8/LARGE/285081602.JPGas an example.Capacitor C12 on the 475 part no. 285-0816-01However, C12 is drawn as a regular two-terminal capacitor in the schematic.

author: coppercone2
author_rank: Super Contributor
timestamp: October 20, 2024, 02:08:37 am
content: I mean, unless your being paid by the hour, there is every reason not to bother finding a symbol etc.also that is a nice capacitor

author: Kurets
author_rank: Regular Contributor
timestamp: October 20, 2024, 06:23:14 am
content: The andswer is in the video. Next to the 2n7002 is a three pi tantalum capacitor. These were common as a means to remove the risk of assembly errors. It is amusing how unhelpful most answers to the question are.

author: shabaz
author_rank: Frequent Contributor
timestamp: October 20, 2024, 07:41:05 am
content: Quote from: Kurets on October 20, 2024, 06:23:14 am"It is amusing how unhelpful most answers to the question are"If everyone was like you, then no one would dare make a suggestion on forums in case it was ridiculed as you did. It's OK to make mistakes. Not all things are life-threatening, such that mistakes must not ever be made.I found all the answers helpful. They all pretty much described valid possibilities. Who cares which one it turned out to be.Not everyone has time to watch a long video, I certainly don't, so I can understand if others don't either.

author: coppercone2
author_rank: Super Contributor
timestamp: October 20, 2024, 06:28:12 pm
content: an axial capacitor with shield to ground would be a better choice for that circuit anyway

author: golden_labels
author_rank: Super Contributor
timestamp: October 20, 2024, 08:21:34 pm
content: Quote from: Kurets on October 20, 2024, 06:23:14 amI was considering that kind too. But in the video we can’t see the belly side of the capacitors, so I couldn’t make a positive confirmation.However, upon closer inspection I must agree. Two-legged components would need to have leads awkwardly bent to fit, or something would need to be very weird with the perspective.Quote from: Kurets on October 20, 2024, 06:23:14 amIIRC limiting unwanted inductance was the advertised goal.Quote from: Kurets on October 20, 2024, 06:23:14 amI like and appreciate your response, thank you for that. But there is no need to deride other people. I have no doubt everybody here honestly tried to help. Let’s not make people more reluctant to give answers in the future, because they experienced negative feedback after being wrong.After all your post is nothing more than a guess too, right?

author: Smokey
author_rank: Super Contributor
timestamp: October 20, 2024, 08:40:09 pm
content: Maybe?https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/MAL205156472E3/5632831

author: inse
author_rank: Super Contributor
timestamp: October 21, 2024, 04:31:27 am
content: Never seen this kind of Tantalums before but pin arrangement makes sense.