On Sat, 13 Dec 2003, John J. McDonough wrote:
> OK, this experiment I've run before.  7805's will valiantly try to pump
> out 5 volts into a direct short, getting astonishingly hot in the
> process, but the programming LED would still light, so I had some 5
> volts there.

Decades ago for a rush prototype I had slapped together a quick 5 volt
supply using a 7805.  I turned the prototype on and it acted in very
strange ways, I couldn't make any sense out of what it was doing, nothing
was right, signals were there, then they weren't, it was operating but it
wasn't...

Finally I diagnosed what was going on.  The prototype was using more
current than the 7805 could adequately supply, with the small heat sink I
had used on the regulator and the unregulated voltage I was feeding it
with, it was turning on, powering the prototype, overheating in a little
under a second, switching itself off, cooling down in about a second,
turning itself back on, heating back up...

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