More 11/750 PSU Qs

From: Davison, Lee <Lee.Davison_at_merlincommunications.com>
Date: Tue Apr 16 18:12:22 2002

        .. (and, as lab supplies, they don't get confused
        by being fed backwards, so I don't need the diodes)...

Lab supplies have the diodes built in on both the + and - legs.

        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.

        So, I think if you use PSUs that have a current limiting circuit
that is
        not only for short-circuit protection, but engages smoothly as
current
        approaches the continuous rating of the PSU,

You don't need this, in fact it can cause problems with groups
of supplies hunting between Ilimit and Vlimit as load is transfered
between them.

        you should be able to connect them in parallel with said
        diodes. Of course, these PSUs will not be the cheapest
        devices...

As long as you match all the supplies to closer than the vf
drop of the diodes nearly any supplies can be connected
this way.

        However, this setup may get difficult if loading varies widely.

Usually it isn't a problem as long as there is no minimum
load requirement for the individual supplies.

        Another problem might be shutting down the entire system if
        one or more of the supplies fail:

Use enough supplies so that one faliure is tollerable. you can
then hot swap the dud supply.

        you wouldn't want the remaining ones to supply as much
        current as they can, keeping the voltage only half-way up
        and running your circuitry in brown-out mode.

If the outputs are overcurrent protected then a faliure of too many
supplies should shut down the whole thing. Trouble is it often
doesn't work that way.

Lee.



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Received on Tue Apr 16 2002 - 18:12:22 BST

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