On Tue, 2007-01-30 at 14:04 -0500, David VanHorn wrote:
> >
> > Other than that, I've heard a few stories online of troubles caused
> > by excessive bypassing causing oscillations, etc, and I'm sure it's
> > possible, but in my relatively short time I haven't run into it.
> 
> 
> I saw one case of a 7805 that was very hot on a light load.
> The bypass cap had gone bad, and the reg was oscillating at about 2 MHz,
> with several volts P-P.
> People forget that these regulators are high gain amplifiers with phase
> shift.

I'm surprised to hear that from a 7805, they generally can survive a
nuclear blast without doing anything weird... :)

That said, you are absolutely correct. This issue is especially worse
with newer linear regs. If the data sheet specifies a certain type of
cap you better use it. Same with ESR recommendations. It may seem like
"just a cap", but put the wrong one in and VERY bad things can happen!

Still, a 7805 oscillating at 2MHz, that's a surprising output from that
chip! I wonder if there is a way we can harness this effect... (putting
on my Doc Brown hat). TTYL

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