More 11/750 PSU Qs

From: Davison, Lee <>
Date: Wed Apr 17 17:58:04 2002


>> running only one in "voltage source" mode, the
>> other(s) in "current source" mode effectively.

> This is how any group of paralell power supplies works.

        And this requires the over-current protection to not shut
        down the individual supply, but instead have it contribute
        as much as can safely be done. On the other hand...

No. All the supplies are set up as constant voltage. They are
paralelled through either load share resistors or blocking
diodes. Each can be overcurrent lockout protected as the
forward drop of each diode or resistor ensures load sharing.
No single supply will be at it's current limit. This is not a
theory, this is how regulated paralelled power supplies work.

        This will be inhibited by the above-mentioned load-sharing
        feature, so you need some kind of "communication"
        between the supplies in order to be able either to share
        load or to completely shut down all others instead of
        running them in current-limiting mode after some have

None of the supplies are ever run in current limit mode, they
are all, always, running as voltage sources. In th eevent of
faliure once the remaining supplies can no longer cope
with the load they all shut down in short measure. No
communication is needed.

> Use enough supplies so that one faliure is
> tollerable.

        The only thing that needs preparation for this may
        be mechanics: you wouldn't want to try unscrewing
        thick power wires and risking them to touch any
        other metal parts inside a running system...

You use off the shelf supplies and they each plug (via the
load share network) into the output busbar. No bolts, no
screws, just (un)plug and go.

        So, I think the bottom line is: running PSUs in
        parallel is something that really can be done,
        but there are several bells and whistles you
        need to take into account.

It's really quite easy, AT type 'dumb' switchers just need
a blocking diode, make sure though that you turn them
all on together.

         .. We get to a point where a microcontroller makes
        sense to control this, and I have seen this in real

As have I. There is nothing more anoying than the faliure
of a system because someone decided a microprocessor
was needed where Kirchoff's laws would have been sufficient.


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Received on Wed Apr 17 2002 - 17:58:04 BST

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