[Ktechlab-devel] Better modeling of properties.

[Alan Grimes]

It seems I've accidentally been sending messages to Dan instead of to
the list. If anyone wants to hear about my experience trying to use an
inductor, my current schematics, or my build problems, speak up...

I've been studying the implementation of element, which seems to be the
base class for just about everything, and I have a number of concerns
about various design decisions.

1, probably most important: _EVERY_ part has at least three static
properties and three dynamic properties. these are:


STATIC		DYNAMIC
Resistance	voltage potential
Impedance	current
Capacitance	charge (stored energy)

Lets consider the attached circuit,

It's power supply can be expressed in terms of the above,

No battery I know of is a perfect conductor, so it has an internal
resistance. In the case of a current SOURCE, the resistance is NEGATIVE.
Lets say it has a negative impedance of -100ohms. (meaning it will only
supply 2.5V to a 100 ohm load...)

It can't produce an infinite current immediately (or at all!), so it has
some inductance.

And finally it has a capacitance, which is, for the duration of its
service life, equal to its output voltage.

The capacitor has two kinds of resistances, the resistance of it's
plates and the leakage resistance, (R_leak).

In audio, it is often necessary to use capacitors with low ESL to
provide power for high-frequency waves and, in power supplies,
capacitors with low ESR to handle demanding loads in a rectifier. Often
these capacitors can cost $70-$120. It is important that these
properties be well modeled so that the designer can know what his design
really requires.

In the amp I'm working on, the interstage coupling capacitors need low
ESL and ESR so that the power stage is adiquitely driven. I require low
ESR capacitors in the power supply to handle the incomming waveform and
turn it into nice clean DC. The capacitor that I put around my dummy
power section is called a snubbing capacitor, it is a low ESL capacitor
that complements the low ESR capacitor in the filter. It's job is to
handle instantanious voltage changes.

For example, I'd tend to snub a "JENSEN 68091" with an "AURICAP-64233"

2. I notice that the element class seems to have a lot of information
about the selection of components available. I don't think this is a
good design decision because it makes the code more brittle. Ideally, it
will be possible to add arbitrary new components without changing the
base class...

3. Elements should not know about "ElementSet", they only need to know
about their most immediate connections and a few environmental
parameters such as the temperature of the chassis (which I noticed was
implemented as a constant! =0  ) -- what is a constant, should be a
constant, what isn't a constant, shouldn't.


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