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From: Jon Kirwan on 4 Mar 2010 23:45
On Thu, 4 Mar 2010 18:25:13 -0800 (PST), George Herold
<ggherold(a)gmail.com> wrote:

>Thanks Jon, I got it. The voltage 'gain' happens after the switch is
>turned off.

I suppose, but I probably wouldn't ever use the word "gain"
here. It's really not what is happening. It's the sudden
removal of an energizing EMF, which was used to transfer
energy into a magnetic field at a geometric rate (linear rate
of change in current that is then squared, suggusting that
the total energy stored is proportional to time^2) and the
removal of that EMF and the consequent and necessary collapse
of the magnetic field, whose energy _must_ then go somewhere.

Electronics uses different names for the exact same effect,
depending on when and where and why it happens. Still just
the same thing. But I can't recall "gain" being used here.
Maybe I'm wrong about that, though. I certainly don't have a
comprehensive view of their use of terms.

You often find capacitors nearby where this is happening.
There's a good reason why. And not only because one might
which to convert the magnetic energy into charge storage.

While the inductor's equation of dI/dt = V/L is true enough,
there is still an "I" that must initially continue. Without
a C nearby, with its equation of C*dV/dt = I, there is no
really good place to get that "I" flowing once the EMF is
switched away. With a C there, all that is needed is some
dV/dt to meet the need and you can choose a C that provides
for a reasonable dV/dt for that initial "I" value. And the
inductor is quite able to cause that kind of changing V. In
contrast, with an R it may need a very high and instantaneous
V, but it always takes time to do that and that can be a
problem (which means some other small trace C somewhere will
have to do the job to give it that time.) A C is nice near
switched L's.

Jon
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