[sdiy] mosfet/cmos opamp

[David G. Dixon]

> >Based on this, for yours I calculate a charging time of 5nF/1mA = 5 us/V.
> >
> >I'm driving mine from a TL074 opamp wired as a buffer, so I've got a
> maximum
> >of about 25 mA of driving current at the lowest load impedance (+/-8V
> >maximum output to a 300R load, according to the datasheet).  If that were
> a
> >constant, then the charging rate would be 100nF/25mA = 4 us/V.
> 
> Ah, so we end up at the same place!

Evidently.  I'm just not sure that any of this is correct.  (Actually, yours
looks pretty safe because of the constant current source, but I'm thinking
mine might need some actual calculus to get the right answer....  Then
again, I never gave a second thought to the charging rate before you
mentioned it, so I'm thinking I probably won't bother.)