[sdiy] mosfet/cmos opamp

[David G. Dixon]

> I look at it differently.  I think of a current source driving the cap, so
> the time is ~CV/I.  In my case I'm driving at a bit under 1 mA (driven
> from
> an OTA used as a current switch) and the numbers look about right.  So I
> would look at what the current limit of your source is.  This may be where
> my thinking is wrong; you may have a lot more drive current than what I'm
> thinking of.

Yes, that makes more sense (at least if you're charging with a constant
current source).

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.

This is making me feel like Gumby Electrical Engineer ("My brain hurts!")