[sdiy] How is the feedback loop of the exponential converter analysed?

[Spiros Makris]

yeap, it shows up fine for me. Thanks, Ben!


On Mon, Jan 27, 2020 at 1:25 AM Ben Stuyts <ben at stuyts.nl> wrote:

> I’m trying to track down the problem with certain images not showing on
> the list. Spiros has sent it to me separately and I’ve turned some knobs on
> the mailing list control panel. Hopefully this time it gets through:
>
>
>
> On 27 Jan 2020, at 00:01, synthdiy at adambaby.com wrote:
>
> Spiros that image isn’t showing for me
>
> On 27 Jan 2020, at 6:43 am, Spiros Makris <spirosmakris92 at gmail.com>
> wrote:
>
> Hello!
> Attached is a barebones version of an expo converter realised with PNP
> transistors. Thermal circuitry is omitted for clarity. The type of HF
> compensation shown is not important(?).
> I know from my experiments that a TL082 (usually?) needs a feedback
> capacitor to ensure it does not oscillate in this configuration. I have
> built it before and arrived to 47p for the stability capacitor, which keeps
> the loop stable but allows a bandwidth of ~15kHz (Iout/CV), if memory
> serves me right.
> How could someone estimate that value using pen and paper calculations?
> Or, at the very least, some slight assistance from spice, yet not just
> brute force it with trial and error? What qualities of the opamp matter in
> this application and what are the tradeoffs?
>
> Any resources or explanations are very welcome.
>
> Regards,
> Spiros
>
>
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