Capacitor symbol: third lead or a rectangle below

[golden_labels]

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

[Andy Chee]

I'm inclined to think that it's a typesetting error, essentially a graphical publishing error.

[Gyro]

Yes, it looks like a 'typo' to me. I can't see something as small as a 1uF 35V electrolytic / tantalum having three legs.

[golden_labels]

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.

[Andy Chee]

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.

[T3sl4co1l]

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 footprint
3b. ...because it's a multi-pin type (e.g. electrolytic with extra base pin(s), tantalum with polarity compensating footprint, etc.)

Tim

[David Hess]

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.

[golden_labels]

Thanks for the responses. So I’ll assume it’s indeed just a mistake.
(more below)

[coppercone2]

I think they just want a axial capacitor with shield to ground, it makes sense to a amplifier

its a RF design if its on signal path and their going to make it specific

especially with a FET input

[BlownUpCapacitor]

I think they just want a axial capacitor with shield to ground, it makes sense to a amplifier

its a RF design if its on signal path and their going to make it specific

especially with a FET input

I 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.

See https://www.qservice.tv/N_PICS/PICS_TEK_SPARES/ALL_8/LARGE/285081602.JPG as an example.

Capacitor C12 on the 475 part no. 285-0816-01

However, C12 is drawn as a regular two-terminal capacitor in the schematic.

[coppercone2]

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

[Kurets]

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.

[shabaz]

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.

"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.

[coppercone2]

an axial capacitor with shield to ground would be a better choice for that circuit anyway

[golden_labels]

The andswer is in the video. Next to the 2n7002 is a three pi tantalum capacitor.

I 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.

These were common as a means to remove the risk of assembly errors.

IIRC limiting unwanted inductance was the advertised goal.

It is amusing how unhelpful most answers to the question are.

I 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?

[Smokey]

Maybe? https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/MAL205156472E3/5632831

[inse]

Never seen this kind of Tantalums before but pin arrangement makes sense.