less hum: switching power supply?

[Haible Juergen]

	>Minimum load current is something I have seen on regulator data
sheets
	>but I have never seen voltage excursions at the output of
regulators we
	>use. It is probable that the minimum current requirements are being
met.

Brief glance at http://www.national.com/ds/LM/LM340.pdf
Scroll to LM7800C, example 15V type.
The input voltage range is 17.5V ... 30V  _under_the_condition_that_
output current is between 5mA and 1A.
So, if you either go outside the input voltage range or outside the
output current range, you're out of specs.
The chips are better-natured than that, however. In practice, it
they often (always ?) work when the output current is lower than
5mA *IF* the input voltage is in the lower range. (Empirical
results were posted some months ago -> archives)
But apparently high input voltage (within specs) *AND* low 
output current (below specs) are a condition that's too much
for these chips, and they show the dreaded high output voltage
fault.

No idea if this is the ultimate truth - I guess not - but these
are my conclusions at this point.

JH.