28 Apr
2014
28 Apr
'14
4:58 p.m.
On Apr 28, 2014, at 3:06 PM, Eric Smith <spacewar at gmail.com> wrote:
On Mon, Apr 28, 2014 at 3:24 PM, Guy Sotomayor <ggs
at shiresoft.com> wrote:
Sorry, wasn't clear.
The modular supplies that I'm looking at can put up to 6 supplies in one
chassis. Each individual supply is independent and has their own voltage
sense. So in one chassis there will be 5 -5.2v suppliles. Each will be
independent with their own voltage sense. I'll duplicate that chassis configuration
to get to the requisite 10 -5.2v supplies. I'll be using a 3rd chassis for the 4
-2v supplies (each with their own voltage sense).
The supplies that I'm looking at right now is the UltiMod series from Ecelsys.
I plan on using 2 UX6 chassis with 5 XgH modules in each and 1 UX4 chassis
with 4 XgG modules. Another nice thing is that they're available from DigiKey.
They seem to have all the right specs and it should be relatively easy to swap
out the H761 and replace it with these as it should have the right number of
connections, sense lines and control signals.
The spec on the ripple is 20MHz and 100mV (or 1.0% pk-pk).
TTFN - Guy
My plan for my 2065 at the moment is to replace
the entire H761 with 3
modular
switching power supplies. 2 to supply the 10 -5.2v supplies and 1 to
supply the
4 -2v supplies. All told they'll draw ~2200W which is a far cry from what
the H761
draws.
I recommend using 13 separate power supplies with remote sense inputs
rather than 3, so that you have proper remote sensing for each DC supply
rail. When I looked into that some years back, it was actually less
expensive to get ten 5.2V 35A supplies than two 5.2V 175A. 5.2V is within
the adjustment range of most 5V switchers that have any adjustment
capability, but remote sensing is important because even with the 10-guage
power cables there's a nontrivial voltage drop (around 150 mV according to
one field service engineer). That doesn't sound like much, but ECL
requires much tighter voltage margins than TTL. Of course, without remote
sensing you could just try to adjust the supply higher (e.g., 5.35V if the
drop is 150mV), if that's within range. If you use fewer, beefier
supplies, then you have to make sure that the drop is uniform on each cable
fed by the same supply.
Similarly, I expect that separate 2V 35A switchers will be less expensive
than a 2V 140A. However, if you've found otherwise, I'd be interested to
hear what power supply models you've found.
The ripple and noise from typical switchers is higher than the ripple from
the H760/H761. I'm not sure how much of a problem that will be, but I've
been told that DEC used linear regulators specifically for that reason.
That's why the replacement regulator I designed uses 12 phases; the 35A
current requirement can be satisfied with a single phase, but more phases
results in lower ripple, so the output filtering is more effective.
Compuserve replaced their power supplies with switchers, but I've never
found any information on the models/specifications/performance.