@Nucu @idiot

I agree: nothing obviously wrong with the schematic.

Any chance there are unwanted current return paths that could occur during plug-in? (Ex, if 24v makes contact first, is there some other unwanted DC/AC return path?)

Isolated AC/DC power supplies have a Y capacitor to provide an AC (high frequency) return path from DC ground to chassis ground. This DC side of the Y capacitor can be charged relative to chassis ground. If there is another DC return path for your device to chassis ground, (or high enough capacitance AC return path) and +24V makes contact first, you can get a brief spike of higher-than 24v , or lower than 0v, on the input, possibly enough to trigger latchup.

Adding a zener clamp at 30V or so, as well as some low ESR/ESL caps on the input could help suppress; but you might also consider a discrete mosfet-based protection circuit ahead of the switcher that has higher/reverse voltage tolerance, and only provides power to the switcher after a small delay.

@azonenberg
There’s usually no requirement to use TF-A or uboot; though I would recommend you consider uboot as its presence is *really* nice for dev/debug work (TFTP booting an image rather than waiting for a reflash, for example).

I’ve done a fair amount of Cortex-A bootchain work; feel free to ping me if you want.

@azonenberg @emaste @petrillic also, with regards to potentially needing oil mist for compressed air regulators; there are lots of generic compressed air systems that are oil free (anything painting, for example).

I have never seen a regulator call out that it requires inline oiling.

@azonenberg @emaste @petrillic my understanding is that pressure regulators are gas type sensitive only due to the fittings (designed for a specific tank type) and material compatibility.

There shouldn’t be a material compatibility issue with N2 for any compressed air regulator; so I think you should just look for a generic compressed air regulator for your target pressure.

Flow regulators are gas type specific because they are differential pressure regulators looking for a differential pressure across a calibrated orifice, which is gas type specific.

@azonenberg @emaste @petrillic

Most of them. Check out SMC pneumatics regulators for example. I do exactly what you are suggesting for my SEM: bulk N2 tank pressure down to 50psi or so, final precision regulator for the 3psi purge pressure I need. I can get part numbers later if desired.

@ryanc if you don’t mind used and a clunky CLI, the Aruba MAS 2500/3500 series are dirt cheap (I paid ~100 for a 48port with POE).

If you (or anyone else) goes this route, ping me for a firmware patch that removes the SFP/transceiver limitations.