@Felthry Also re: this, can current transformers not give you high enough bandwidth?

@zetasyanthis our target is 30MHz, and it's going to be on top of a DC bias of 100A--that's going to saturate most cores

@Felthry Ah, I hadn't thought about the saturation issue. Hmm.

@zetasyanthis We considered a Rogowski coil, which is essentially just an air-core current transformer, but, well. Air-core.

@Felthry Hmm. What kind of resolution do you need?

@Felthry Actually: https://www.keysight.com/en/pd-2877524-pn-N7041A/rogowski-ac-current-probe-30-mhz-600-a?nid=-32553.1229529&cc=US&lc=eng

@zetasyanthis Our lab (unfortunately) uses Tektronix scopes mostly (we don't like tektronix as much as agilent (no, keysight is a bad name, I'm calling it agilent)), so let me see if they make one of those...

@Felthry I don't see why tek vs. agilent is an issue there? It just outputs a BNC. And there's a whole series, looks like. https://www.keysight.com/en/pc-1659326/oscilloscope-current-probes?cc=US&lc=eng

@Felthry Also, fyi, most oscilloscopes are 8 bit

@zetasyanthis Yeah, I know--I think we have some really expensive sixteen-bit one somewhere though

but also we're interested in lower frequency stuff, which means you can increase the ENOB somewhat with averaging...or something? signal processing stuff is complicated

@zetasyanthis current probes almost always use some proprietary connector on top of the BNC though? I know the current probes we have already can let you know when the jaw is open for example

@Felthry "Compatible with any Keysight oscilloscope with a 1 MΩ input BNC" (Which means any. The picture shows a normal BNC cable.)

@Felthry If you click on the link, you'll see. :P 600A, 30Mhz.

@zetasyanthis Ah, didn't realize I had to enable javascript to see the iamge, that's weird

@Felthry Oh, that kinda is. Either way, I think that does what you want? There's a 300A model too. Not sure on the resolution. You'll have to check.

@zetasyanthis Possibly! The price is a bit ehhhh though--we'll focus on designing the buck converter first and then get around to metrology. Will leave a spot for current measurements.

Fair. Keysight's stuff is pricey, but it's good at least.

I'm also a little curious what this is for. I've designed buck regulators before (and was actually working on a few just the other day), but 100A is quite a bit.

@zetasyanthis you managed to lose the @!

Research on three-level buck converters, specifically circulating currents when using multiple in parallel, as well as how to mitigate problems with neutral point drift.

This is based around DC power transmission systems, as used on some ships. The idea is that this small(!) device will have a 10kW max power output

@zetasyanthis The lab is also heavily focused towards EMC (i.e. compliance with UL, FCC, etc standards), and conducted emissions are legally defined as undesired harmonic content up to 30MHz either on the output or back up the input (or through grounding straps, or...). That's why we're looking at 30MHz bandwidth specifically.

@Felthry Oh, oops! And okay, that's pretty neat! I've dealt with 12V DC distribution in computer racks before (and am dealing with it now a bit), but nothing on the scale of a ship. (I think these power shelves are about 15kVA each. Unsurprisingly, Delta makes them.)

@zetasyanthis Actually, looking into it, it seems like Tek sells the _exact_ same current probes, just with a tektronix logo instead of a keysight one on them

I assume they both buy from some third-party manufacturer and put their own logos on them.

@Felthry XD

@Felthry I'm not that surprised. Even Lecroy rebrands some of their probes.

@zetasyanthis that rogowski probe you recommended has a minimum detectable current of 250mA, which suggests it's probably got a pretty high noise floor unfortunately. Not sure how good you can get with rogowski coils, though.

@Felthry Ah, dang. They have a few probes with different sensitivities. Might be another can help.

@zetasyanthis I think poor noise performance is kind of baked into the concept of a rogowski coil unfortunately. not having a magnetic core means they don't concentrate flux into the coil, which is what makes cored devices work so well

we need better paramagnetic materials!

@Felthry I mean, there are current transformers too. (I checked digikey, but those go up to about 1 kHz max at the current you're wanting.)

@zetasyanthis Yeah, that's the problem! I'm wondering how hard it would be to roll our own current transformer, at this point, but I don't know the first thing about high frequency magnetics

Some kind of current shunt resistor might be the only option

@zetasyanthis Not sure. Fairly high; this is for a research application and we want the best metrology we can manage. Twelve or sixteen bits, perhaps? At sixteen, you'll definitely be losing a bit or two to noise (I won't pretend we know the first thing about designing a PCB to mitigate noise)