fried VME modules

OK, that's fine. But it says 2v to 4v gate voltage, not 5.5v

Yes, it does. Take that up with Larkin. ;-)

Yes, it does require close to 5.5v for meaningful current. I would pick another smaller one. Just use more of them.

Must be countless ways to do that. Here is my first stab at it:

piglet

That's the gate threshold voltage, what it takes to get 250 uA drain current.

I want hundreds of amps.

Most of those circuits will work once, namely destroy the SCR.

Why don't you just turn off your device instead of short circuiting the supply?

CH

Yes, and by 6-7V when the payload silicon is starting to hurt the FET will be conducting very well. I think the scheme will work fine.

piglet

I think JL wants a simple pragmatic retrofit option to an existing product. A beefy shunt clamp could be simple enough for a user to fit themselves.

piglet

søndag den 6. juni 2021 kl. 10.06.39 UTC+2 skrev snipped-for-privacy@highlandsniptechnology.com:

how big is the supply?

and if you just short out the supply rather than just a linear shunt, isn't it likely to do weird things?

The gate driver I did here regulates to a constant voltage, but is probably needlessly complicated for your clamping needs:

These have much lower gate drive voltage for rated current, perhaps higher for surge, if you want to stay with 3v to 4v drive.

Diode DMN3020UTS TSSOP-8 14A Diode DMN2015UFDF DFN2020-6 14A Vishay SiA448DJ SC-70-8L 12A AlpOmg AO6404 TSOP6 8.6A Rohm RQ1C075UN TSMT8 7.5A ST STT5N2VH5 SOT23 5A

For how long?

You need a fuse to save the SCR as well. Sustained hundreds of amps could very well destroy the PCB traces also.

Good idea. The customer could just cut the AC line cord.

I'm not sure what its peak current capability might be. Hundreds of amps maybe for some milliseconds.

I'm proposing to clamp the +5 rail at about 5.5, not crowbar it.

If it blows a fuse, it works just once.

And I don't want to remove the VME crates and disassemble the power supplies and add a huge fuse somewhere. May as well redesign the supply to not spike when the switch is teased.

The hazard seem to happen with an MTBF per crate measured in decades, just often enough to blow up our modules in one of many crates every few years.

Sounds like they hacked into the ENABLE of a buck controller, letting something float, so that during start-up it's letting the unregulated DC get thru the LC onto the output before it starts regulating.

Same if it blows the PCB traces. How big are you planning on your traces to handle hundreds of amps? I think at least 50mils for sustained 5A.

You have to tap it at the supply lines anyway, if you don't want to blow up your VME bus lines.

Could be power surge on the AC line.

That's nice. I used a fixed bandgap, an LM4040-5 1% part.