@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

@Felthry Actually, yeah, that could work. You could A/C couple off the current sense resistor before driving an op-amp with it, potentially. Definitely want some limiting resistors on those lines, too.

@zetasyanthis Problem then is the preamplifier that you'll pretty much definitely need

you need a high bandwidth, extremely low noise op amp, _and_ some way to power it while it's floating at potentially up to 500V (honestly considering a CR2032 for that if we go down that route--it's for research, not a permanent installation, and isolated switching power supplies inject all kinds of noise), and then some way to level-shift that signal down to something we can use as an input

@zetasyanthis In any case, the metrology is probably going to wait. We do have high voltage diff probes so maybe those will be sensitive enough? The problem lies in trying to AC couple a current signal, which means using inductors, and inductors can become very capacitive at high frequencies.

@Felthry Yeah, fair. (And sorry, just thought that's a really cool problem and started digging into it. XD)

@zetasyanthis oh I agree it's a really fun problem!

@zetasyanthis we've learned a lot of interesting things in the process of designing this too, like "actually it turns out you can just buy 2500μF film capacitors" and "instrumentation amplifiers are very low bandwidth" and "holy _fuck_ silicon carbide MOSFET modules get expensive"

@zetasyanthis Also, apparently they make power JFETs designed for switching, which is Definitely A Good Idea to have a system where losing power to your gate drive means you instantly create a shootthrough condition

@Felthry Hahaha. Oh god. IGBTs please! XD

@Felthry And this kind of thing might work as an analog optoisolator too, depending. https://electronics.stackexchange.com/questions/126610/need-an-optocoupler-for-getting-directly-proportional-output-galvanically-isolat

@zetasyanthis or enhancement-mode MOSFETs!

@Felthry *nodnodnods* Although now you're giving me flashbacks to designing a 150A rated H-bridge a while back for some student robotics work. (Mine was the first our team designed that didn't just fucking explode when the motor stalled out. XD)

@zetasyanthis oh yeah, another thing about this design project, we're using CAS120s as the switching modules, which means that _just the switches_ of one converter come to a total of $660

the reason we're using these is so we can have extremely high switching frequencies; the design right now is based around a 25kHz switching frequency and we plan to increase that to 100kHz.

@Felthry Man, I'm spoiled at the lower current end, where you can just run at a few MHz and not care in converters. Can see why you don't do that at the higher end though.

@zetasyanthis For one thing, switches can't switch fast enough! Big FETs means big gate charge.

The prior work on this type of thing has been around 5kHz switching frequency simply because silicon devices at this sort of power level are not fast enough for much more, you'll lose all the magic smoke quite rapidly

The reason we can do twenty times that is because we're using silicon carbide modules, wide-bandgap semiconductors--and WBG means high speed

@Felthry Ah, okay, that makes more sense! Some of this is black magic beyond my experience. :P

@Felthry And since you're doing EMC work, the sheer "oh god what" in this will make you laugh. :P https://www.youtube.com/watch?v=S5uiupJQc9M

@zetasyanthis oh, clive reviewing awful ebay/aliexpress crap is always a good watch

@zetasyanthis ...it's literally just an electromechanical device? Wow.

@Felthry It's both brilliantly simple and absolutely horrifying! :D

@zetasyanthis you could use it as a spark-gap transmitter!

@Felthry I mean, you can do the tried and true "put a nice ADC on the board with the op-amp" and then run the digital data through an optoisolator?

@zetasyanthis Might have to, but _oof_ 30MHz ADCs won't come cheap