[time-nuts] Parallel voltage regulators

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Oct 24 20:51:47 EDT 2007

Magnus Danielson wrote:
> 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
> transitor(s).
> 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.
> Cheers,
> Magnus
Hej Magnus

Using a 723 correctly configured with a low pass filter on the reference
is a very low noise regulator solution with its output noise at least
20dB lower than that produced by a typical 3 terminal regulator.

Most of the OEM open frame linear supplies use 723 regulators with
external (to the 723) series pass transistors.
These regulators have varying degrees of sophistication, some even use a
zener plus emitter follower preregulator for the LM723.
Some foolishly omit bleeder resistors across the reservoir capacitors
which can lead to damage when making connections after powering the
supply on and then off as the residual energy stored in the reservoir
capacitors is more than sufficient to destroy the 723 should the output
terminals be shorted.


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