At 08:07 AM 1/4/2012, you wrote:

>On many regulators the ESR of the vreg output cap must be within a certain
>range, if it's lower or higher it will oscillate.

That's for LDOs.. which are notoriously fussy about the output capacitor
because of the way they are made. The 78x05 is incredibly stable over an
enormous range of input and output impedances. Cheap too. That's partly why
they're still in wide use, more than 30 years after being introduced.

I can only conclude that there must have been some bad ones out there,
because I tried a few name brand ones (JRC, National and SGS, IIRC) and
was unable to get them to do silly things even with the most
pathological tricks (series inductors on the input etc.). I've only heard
anecdotal evidence that it is possible.

As one data point, there's a product I designed that uses a 78M05 with
virtually no (external) load AND no bypass capacitor and it has shipped
tens of thousands with no problems.

As far as the original question goes- recall that there is an internal
divider chain on the output that nominally draws 0.6mA~1mA or so, so you ca=
n't
really operate the regulator with less load current unless you have access
to some pretty fancy tools. ;-)

--sp



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