"Ian Iveson" wrote in message k...
"Fred" wrote in message ...
"Ian Iveson" wrote in message news
Thanks Fred
Sounds like a very good current regulator to me,
capable of a 100:1 dynamic range. You, as the
designer, control how low the dynamic R goes in
your circuit by controlling how low the dynamic
voltage across the device goes during operation
- the lower the instantanious voltage, the lower
the instantanious R required to maintain the
design current.
The same would be true of a resistor. The greater the voltage you have to play with, the greater you can make the resistance for
a given required current.
I hadn't read far enough into the datasheet to see under what circumstances that dynamic R might vary, so thanks for the info.
But is 100k OK? Fine if it were a resistor in most cases, IMO, and for most ppl maybe fine even for a non-linear device. But I
would bet that some would argue that 100k is not great enough to guarantee that the sound of silicon can't seep in under the
back door.
OTOH, I have seen many claims that simple discreet silicon circuits achieve many Megohms, but with no mention of frequency
response, as if it didn't exist or didn't matter.
If the ixys device achieves 100k at all frequencies of interest, it's just about good enough, IMHO. It's certainly convenient.
cheers, Ian
The IXYS device achieves many megohms at all frequencies
of interest, Ian, unless your only frequency of interest is 0 Hz.
It's a current regulator, not a solid state resistor.
The AC resistance, or impedance, of a current regulator
is in the megohms because the current through it doesn't
change when the voltage across it changes - it looks like an
open circuit in that respect. But it does conduct a (fixed by
the designer) DC current, so depending on the voltage across
it at any given moment, one can calculate a DC resistance for
that moment by ohm's law. But it still looks like an open circuit
to an AC voltage because, again, the changing voltage fails to
cause a changing current as it would in a resistance.
DC resistance calculations have about as much bearing
on current regulator performance as they do on output
transformer performance, only less.
This isn't rocket science, Ian, and you don't need calculus to
understand it. It's covered in any modern electronics text.
All of which appears to me as a total nonsequitur in toto, and pure nonsense in parts.
You won't find understanding in books, particularly if you have difficulty reading. You need to think a bit too.
I took it that "dynamic R" meant the dynamic resistance of the current source. Since it is given as 100k max, and that is very
different from your "many megohms", I felt it worth discussion. I may be mistaken, but you have failed to spot where my mistake
is, smart-arse.
And you are wrong, but I can't now be arsed to tell you where.
Final words of wisdom from someone without a clue. Let us
know if you figure it out.
Fred
bye, Ian