VAX-11/750 power supplies

Mattis Lind mattislind at
Wed Apr 8 14:37:41 CDT 2015

2015-04-08 18:46 GMT+02:00 tony duell <ard at>:

> > However looking in the print set the diode is listed as 1114197-00 with
> the
> >
> > Is the Unitrode USD5096F a 60 Amp diode? This link tells me it is a 35A
> > diode:
> >
> >
> > and so does this link:
> >
> > /271653646843?pt=LH_DefaultDomain_0&hash=item3f3fd1b1fb
> It's possible (although unlikely) that DEC selected diodes that could
> stand 60A for this location from what were
> nominally 35A parts. More likely, I think, is that what is _needed_ here
> is a 35A diode (what is the output current
> of this PSU) and that the originially specified part was a 60A one (which
> is clearly be OK). Then somebody found
> a 35A part that would work.

The problem I have it is impossible to confirm what the rating is for this
diode. I simply cannot find the data sheet.

The 5V PSU uses four of these diodes and the max output is 135A. The 2.5V
PSU uses three diodes and the max output is 85A.

> Of course you can always fit a higher current diode than is strictly
> required (provide the switching times are
> fast enough in a circuit like this). My guess is that since diodes have
> improved since the days of the 11/750,
> you could fit modern 60A Schottky diodes without problems.

I will try to run it with the replacement USD5096F that I have and see how
long it lasts. It probably depends on how many boards I stuff into the
machine. If that fails I will search for DO5 mount 60A Schottky diodes. If
anyone has a bunch of them at a good price I am interested!

> -tony
> /Mattis

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