Re: day shot to hell

On Sun, 22 Nov 2009 14:10:29 -0800, Joerg <invalid@xxxxxxxxxxxxxxx>
wrote:

krw wrote:
On Sun, 22 Nov 2009 13:32:09 -0800, Joerg <invalid@xxxxxxxxxxxxxxx>
wrote:

krw wrote:
On Sun, 22 Nov 2009 11:17:37 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:

On Sun, 22 Nov 2009 12:12:36 -0600, krw <krw@xxxxxxxxxxxxxxxxx> wrote:

On Sun, 22 Nov 2009 09:26:57 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:

On Sun, 22 Nov 2009 10:10:35 -0600, krw <krw@xxxxxxxxxxxxxxxxx> wrote:

On Sat, 21 Nov 2009 14:14:15 -0800, Joerg <invalid@xxxxxxxxxxxxxxx>
wrote:

[snip]
This one has a problem that the reference shoot up to the VCC rail and
then slowly comes back. IOW it isn't very suitable for power-up
protection or sequencing.
Just sequence its power!
Couldn't. In that case power was the actual control signal and things
had to happen fast, within hundreds of usec. Now they do :-)
I meant sequence the power to the reference. ;-)
Any reference that "shoot(s) up to the VCC rail" should be replaced
with one that doesn't. Where do you buy such crap?

As for fuses, I've always been fond of crowbar fuse blowers when
over-voltage conditions occur. Why lose downstream electronics when a
power supply goes bananas?
I guess that depends on the application. I'm more worried abut
fuse-blowers getting too happy than even attempting to save any
downstream electronics. In my case, the large cost is the service
outage, not the electronics.
I was protecting $1000's of dollars of custom-made stuff. I could
make a 10A fuse element vanish is micro-seconds
(filter-cap-bus-bar-SCR loop) ;-)
The price may be (tens of) $1000s of dollars, but the cost certainly
isn't. ;-) OTOH, a royally pissed off customer might easily be worth
40dB more. The boss doesn't like it when we're the subject of the
television program.

Let's put it that way: If the crowbar trips something else _has_ already
failed. Meaning it's a service call no matter what. The difference
between having a crowbar or not having one could be several thousand
bucks (board repairable versus it being toastissimo).

Right. The difference is the cost, not the price. The cost of the
electronics is certainly not in the tens of thousands of dollars. The
stuff I did where the cost was in the millions had all sorts of belts
on. With supplies rated in the kA, things get smoky fast and smoke
was rather more frowned upon. These weren't jellybean regulators,
though.


With a bunch of hotshot FPGA you can easily get to $1k. Many of my
boards drive very expensive gear.

Sure, the Virtex-IIs and 4's I last used were about $4K each. Even
here a service call at the wrong time (incoming shells) makes that
chump change. That's not the point though. I don't spend a lot of
money to protect bring-up (which was the original point). We'll put
in 0-ohm resistors for debug but that's about it.

BTW, the FPGA I'm most likely to use next[*] is more like $2.

[*] Firmware is so hosed up there isn't much point in making new
hardware to play with.

It can also
prevent plumes of smoke and a rather embarrassing case where the fire
engines had to come out because the automatic fire alarm and the
sprinklers came on, damaging all sorts of other equipment.

Fuses are there to keep the heat, if not a little smoke, inside. Fans
dissipate the rest rather quickly. ;-)


See, that's why fuses are a good thing :-)

I never said I didn't use fuses, only that I don't have any illusions
of them saving electronics. As I said before, their purpose is to
keep any fire inside the covers.

In one of my recent cases the crowbar was put in there because the board
could otherwise take out a $10k laser connected to it. Now that would
really make for a pissed client. Not so much because of the $10k but
because it would take more than a month of leadtime to get a new one.

A false trip on the crowbar has the same effect for us. Show doesn't
go on, customer mad as hell. He doesn't much care if it was $1 or
$10000s of electronics smoking. It's not working.


Mine are working. I've yet to see a false trip of one of my crowbar
designs and it's been >>20 years now.

Circuits that never fail? Why don't you just use one of them on the
power supply, instead? ;-)

It's like the airbag in a car. After it has opened you cannot continue
to drive and it'll be an expensive repair bill but it may have saved a
lot of grief.

If it went off when there was no accident, you still have at least
second degree burns, broken arms and thumbs, and perhaps no ear drums.
...and haven't saved a damned thing.


But they rarely go off without an accident. You need to exceed
life-threatening G-forces to make the sensor signal an accident.

That's the theory. Reality is much different, of course.

See, I can burn strawmen too. ;-)

:-)
.

Relevant Pages

  • Re: day shot to hell
    ... In that case power was the actual control signal and things ... Why lose downstream electronics when a ... The price may be $1000s of dollars, but the cost certainly ... If the crowbar trips something else _has_ already ...
    (sci.electronics.design)
  • Re: day shot to hell
    ... In that case power was the actual control signal and things had to happen fast, ... I meant sequence the power to the reference. ... Why lose downstream electronics when a ... The price may be $1000s of dollars, but the cost certainly ...
    (sci.electronics.design)
  • Re: AC Power Cord for the UK
    ... > Unless this is too far out for the customer, think about installing an IEC ... > power inlet. ... > solution is to convert the amp to US fuses and ship over a box of 5 so the ... Oh yeah, Baynesville Electronics. ...
    (alt.guitar.amps)
  • Re: Has AC had its day?
    ... consider replacing AC domestic power by DC? ... Power rectifiers aren't that expensive now, ... the cost of conversion to A.C. when it was ... small rectifiers in consumer electronics. ...
    (sci.electronics.design)
  • Re: Has AC had its day?
    ... consider replacing AC domestic power by DC? ... Power rectifiers aren't that expensive now, ... the cost of conversion to A.C. when it was ... small rectifiers in consumer electronics. ...
    (sci.electronics.design)