[time-nuts] Parallel voltage regulators

Magnus Danielson magnus at rubidium.dyndns.org
Wed Oct 24 19:45:15 EDT 2007

From: Tom Clifton <kc0vsj at yahoo.com>
Subject: [time-nuts] Parallel voltage regulators
Date: Wed, 24 Oct 2007 16:33:08 -0700 (PDT)
Message-ID: <329129.31442.qm at web37014.mail.mud.yahoo.com>


> A question for those that might know (or have an
> opinion)...  I have in hand an LPRO rubidium reference
> that requires 1.7 amps at 24 volts while the oven
> warms, dropping to 500ma while it runs.
> Can I parallel three or four 7824 TO220 style 1 amp
> regulators with a quarter ohm half watt equalizing
> resistor on the output of each one?

I would not do that, even with the equalizing resistors. The load-balancing
with resistors works when there is a common control-loop, but here you would
have four inter-connected control-loops.

It is not that hard to acheive 2 A at 24 V after all. The old uA723 and
variants would probably do the trick good enought for you with external

I recommend to at least include fold-back for over-current protection, but
adding an over-voltage in form of a crow-bar setup isn't too hard either.
The point of the crow-bar is to cause fold-back and if that fails, blow the
fuse, so include a fuse on the unregulated supply side.

Powerbalancing can be very tricky indeed, and you might end up with either one
having the full load or oscillative behaviours.


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