kablooey
- From: John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 08 Mar 2006 20:10:00 -0800
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
.
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