Big crowbar module for <4VDC?

Also known as a "horse puckey" ?:-)

Heavens forbid we should actually check the unit out and find WHY the fault happened :-(

You seem to have a fixation with arcing. Tell us all how that can happen sourced by a storage cap loaded with a 200V fuse. Remember to stick to your 3.3V scenario ;-)

Crap, Joerg, You've become another Larkin ;-)

...Jim Thompson

Well I confess I can't remember what the OP's application was now; it seems so long ago :)

....(goes up thread)... Aha, it's Joergs big old linear supply he found. Well who knows what he's controlling - ISTR he wanted very low noise, and specifically linear. Sounds fairly exotic to me.

OUTPUT.

IIRC.

I would rather you had put the first donkey into orbit.

OUTPUT.

IIRC.

I tried, but the donkey turned to donkey doo during the acceleration ;-)

...Jim Thompson

We have another donkey. Care to repeat the tests?

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OUTPUT.

IIRC.

A dummy payload?

A good description, or the first sub orbital load dump. If somebody could really design good audio equipment we could even hear his last pathetic, little girlie screams. The Telemetry equipment designs I worked on passed from DC to 40 MHz at -3dB. ;-)

SSSSSHHHHHHIIIiiiiiitttt IIIIiinnnnn SSSSSpppppaaaaccceee!!

I hope you never passed a dump like the Dumb Donkey. Ow!

The agency compliance folks test that stuff.

If a DC power terminal had an intermittent hiccup you wouldn't know either way. That is the most common scenario IME. Because then the guys re-tighten all the screws and replace the panel fuse, after which everything miraculously works again. With your crowbar it doesn't because the fuse on the board is toastissimo but you still wouldn't know what happened.

Not in the 3.3V case. But this thread may be read by younger lads who think "Hey, I'll just do it that way" and then design a telco supply.

As an aside, fuse holders for that kind of current cost a pretty penny.

Oh, I wouldn't mind owning a company like his. But it would definitely not be in S.F.

We had better quality standards than to hire an ignorant shit like him. The European Space Agency threw in the towel on having their equipment built in Europe, and came to Florida for the good stuff.

I would certainly feel very uneasy to rely on a primary fuse to clear a crowbar _way_ downstream :-(

The fuse holder, as well as the fuse, don't have to be rated for the crowbar current. I used the kind that mounts on the PCB, ADJACENT to the storage cap and the SCR ;-)

You seem to have an aversion to that, citing it requires opening the box; but how do you replace the bad regulator without opening the box ?:-)

Not anywhere in Californica!

...Jim Thompson

Occurred to me what I _would_ accept:

Crowbar output of regulator, BUT...

Use an electronic circuit breaker on the primary to quickly open circuit it.

That would alleviate my heartburn over having all that path under stress until a fuse clears.

...Jim Thompson

Not very clear was it?

I mean for electronic circuit breaker to be triggered by same circuitry that triggered crowbar.

...Jim Thompson

From experience: I have an old HP6002A power supply. The previous owner used it to charge a battery. However, he modified to fan to be quiet. So, overtemperature kicks in, crowbar sees Vout > Vset and kicks in as well. Result: traces burned from the PCB but the tiny SCR is still alive.

Again, the predominant reason (by a huge margin) for crowbars to come on that I have seen was when something in the connections became fouled up. This does not have to be any assembly error. Cause #1: High amperage load, sense wires go to load terminals. Big wire lug in the high amp cabling lets go a wee bit, load keeps drawing, sense line signals demand for more juice, linear regulator salutes and steps on it, crowbar sez "Nooo!" ... *shazam*

There is no bad regulator, only a blown panel fuse. Easy to fix: Inspect and correct all connections, replace fuse, flick switch, complete job ticket, hop into truck.

Thompson crowbar: Measure output of power supply ... zero volts. Cycle power ... still zero volts. Bite tongue, suppress expletive. Tell customer that the whole machine will have to be shut down and since Christmas is coming up it'll probably be, oh, early January until the new power supply arrives. Of course they'll be billed for the 2nd truck roll in January. Doesn't create customer happiness ;-)

Well, if they begin hitting the self-employed below the belt too much I might also look elsewhere.

Ah, finally coming over to the output side now? SCNR.

There is a breaker: The foldback current limit. If the pass device has failed the primary fuse has to take care of things. It is _designed_ to do that. It is the same thing as a shorted electrolytic which also has to be handled without engine #3 having to come out with blaring sirens. This stuff gets tested to exhaustion but compliance guys. And yes, I have seen not so reputable manufacturers' supplies fail that test. Told their sales guy "No dice".

The longer the path current travels through the supply to the SCR crowbar, the less I want field techs putting the equipment back in service.

Ideally, to protect high value loads, it might be better to place the crowbar at the load and give them a supply of cheap power supplies. Or at least put a clamp on the load input to hold the voltage down until the crowbar in the PS can remove the supply.

before

if you put the crowbar after the regulator and someon econnects a 24V source (like a truck battery) I think your crowbar will have a little trouble.. in any case that sort of behavior is likely to void the warranty anyway.

On a sunny day (21 Dec 2008 04:50:22 GMT) it happened Jasen Betts wrote in :

Yes, it all depends... a good crowbar, like I have seen in some of the high current 5V supplies, would likely evaporate some battery leads... Thyristors are amazing.

One case, that I have not seen mentioned, and that holds a very real argument for the crowbar at the output, is the circuit where diodes are used to the supply and ground, to limit an input. Now that is the wrong way to do it, one should use a transzorb or zener, but I have seen it proposed here. In case of some input accidently getting a surge (for example touching a mains wire) the low voltage supply will be lifted way above max spec, _if no crowbar at the output_. Blowing a fuse before the regulator does nothing in such a case.

I sort of think, that when buying a supply with 'crowbar', you buy in fact 2 different things in one module. Like the real crowbar, where you throw a piece of copper over the terminals, you could sell a separate crowbar. In fact I was just thinking of doing some market research if I could sell some high power ones.

The trick is to design the path so it can withstand that. There are applications where a screw terminal coming loose should be correctable without losing functionality of the whole installation. Else it would be like an aircraft glass cockpit showing the message "An unknown error has occurred and the program will shut down".

Crowbar at the load is ideal but in this case not quite feasible. The supply must be super quite, hence a linear.