[geeks] Voltage regulators don't!

[Jochen Kunz]

On Fri, 11 Apr 2008 10:30:17 -0400 (EDT)
der Mouse <mouse at Rodents.Montreal.QC.CA> wrote:

> True - but where is the HF coming from?
The air? All your wiring is just an antenna... You have (HF) noise
everywhere. Even without HF you have thermal noise on your DC and this
can be enough to trigger a resonance... (Remember: Ideal noise is just a
mixture of all frequencies from 0 to infinity.)

Also never forget: Every regulator, as beeing an amplifier with feed
back, has the ability to oscilate.

"Oscilators never oscilate, amplifiers oscilate all the time."

> Perhaps odder is that some of my 7805s don't need anything of the
> sort.
It only means that this particular instance of the device happen to work
under that particular circumstance. Depending on load, temperature,
phase of the moon, ... it may fail later.

All these 100 nF blocking capacitors are a _requirement_.
They are essential for correct function under all conditions.
--


tsch|_,
       Jochen

Homepage: http://www.unixag-kl.fh-kl.de/~jkunz/