Re: kablooey

Jim Thompson wrote:

On Wed, 08 Mar 2006 20:10:00 -0800, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

One of my better customers just called. Seems six of my VME arbitrary
waveform generators failed, in the same VME crate, simultaneously.
We're talking over $30K of damage here.

I had them put a scope on the +5 supply and switch power on. It ramped
up in maybe 100 ms, peaked at 5.6 for a few ms, then settled down to
5.1. That's above the 5.5 abs max for my CPU and FPGA chips, but not
really that bad.

So I asked them to switch power off for various times, then back on. A
2 second delay gave 7.5 volts peak. An estimated 0.5 sec delay, as
fast as they could work the switch, ramped up to 8.8. I'm guessing an
optimum brownout might well hit 10 volts.

Dumb switching power supply design... stupid loop dynamics and no
crowbar! I mean, one could easily load a VME crate with $100K worth of
boards. They're ragging the crate vendor next. Don't know who is going
to pay to fix the modules.

I could add a transzorb to my boards, I guess, but the overshoot might
just blow a hole in the board. Transzorb+fuse would work, but that
would be an ugly kluge. 8.8 volts is sort of past my responsibility,
I'm thinking.

John

Sounds to me like a rather ignorant PSU manufacturer.

Nearly 30 years ago I was demonstrating to the digital guru at GenRad
(Phoenix) my "indestructible" PSU.

He proceeded to grab the power switch and rock it back and forth until
"kablooey" and I mean KABLOOEY, KABOOM, molten solder, etc. ;-)

Taught me a lesson... all my future GenRad PSU designs contained a
timer/POR to prevent such switch AND brownout problems from screwing
up the works.

...Jim Thompson
Like most of the best, you got tough lessons like that early in your career
and learned from them.
--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.
--Schiller
.

Relevant Pages

  • Re: kablooey
    ... waveform generators failed, in the same VME crate, simultaneously. ... So I asked them to switch power off for various times, ... optimum brownout might well hit 10 volts. ... Sounds to me like a rather ignorant PSU manufacturer. ...
    (sci.electronics.design)
  • Re: kablooey
    ... waveform generators failed, in the same VME crate, simultaneously. ... So I asked them to switch power off for various times, ... optimum brownout might well hit 10 volts. ... described a rash of component failures that ...
    (sci.electronics.design)
  • Re: kablooey
    ... waveform generators failed, in the same VME crate, simultaneously. ... So I asked them to switch power off for various times, ... optimum brownout might well hit 10 volts. ... logic failures are caused by smps's and random-duration brownouts? ...
    (sci.electronics.design)
  • kablooey
    ... waveform generators failed, in the same VME crate, simultaneously. ... So I asked them to switch power off for various times, ... second delay gave 7.5 volts peak. ... optimum brownout might well hit 10 volts. ...
    (sci.electronics.design)
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