>
> I'm trying to design a linear bench power supply. Given that the bench
> supply can be connected to any circuit (which may have an arbitrarily
> high capacitve load), I need it to be stable. In addition, I'd like it
> to settle within 100 microseconds after a disturbance (either line or
> load).
you aren't going to bring up a huge capacitive load from zero instantly to a
high voltage as you will hit the regulators current limits.


> It seems that it is not possible to achieve stability with very large
> capacitive loads AND guarantee fast settling times, even when the
> capacitve load is less. (This is the way it seems to me after playing
> with it, I have no proof of this yet). This is because you essentially
> have to either design for a particular capacitve load (where you get
> fast response but there is then some max capacitance you can tolerate
> and still be stable) or you have to let the output capacitance
> dominate the response (dominant pole compensation), in which case you
> are essentially designing for the worst case (highest) output
> capacitance and response will be slow.
remember (despite the fact that non switchers are reffered to as linear
power supplies) regulators are by definition nonlinear devices, the output
voltage basically cannot rise over what the regulator is set at because if
it is taken above that voltage the conditions that allow current to flow
rapidly collapse (e.g. if an emmiter follower is the output stage of your
design the base-emmitter junction enters into reverse bias and the
transistor turns off).

generally significant disturbance to the output voltage shouldn't happen in
the first place, thats what the capacitors are for! so your only issue is
rise time on powerup and this is mainly reduced by designing the PSU for
high current output.

i just can't see how you are managing to get instability out of a simple PSU
design unless you are working with seriously broken models, maybe post some
links to the circuits you are considering so we can see for ourselves..

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