[time-nuts] Isolation achieved by opamp based isoamp?

[Didier Juges]

One thing to keep in mind is that isolation through shielding usually
results in much greater capacitance to ground (actually to the shield) from
both input and output windings.

Therefore, the actual isolation in practice is totally driven by how good
the ground to the shield is.

At RF, any inductance in series with the shield's connection to ground will
degrade the isolation. Not a problem at 60Hz, but certainly a problem as
the frequency gets higher.

Didier KO4BB




On Thu, Nov 21, 2013 at 8:28 AM, J. Forster <jfor at quikus.com> wrote:

> Looking quickly at the prints on the site, the isolation is provided by
> the transformer, not the active circuitry. The transistors/op-amps are
> just buffers for the output.
>
> That means that the isolation is determined, for the most part, by the
> transformer design, so:
>
>  A bifilar wound torroid would have relatively poor isolation,
>  Two windings on opposite ends of a ferrite rod much better.
>
> Some (power line) ultra-isolation transformers have a shield between the
> primary and secondary, and I don't see any reason that could not be done
> at RF. The objective is, of course, to minimize the capacitance between
> the windings. Topaz got 0.001 pF on a 1 kW unit as I remember.
>
> -John
>
> =================
>
>
>
>
>
>
> > Hi,
> >
> > I'm curious about the level of isolation that is achieved by an opamp
> > based
> > isoamp. I'm referring to ones described here on Bruce Griffiths' page:
> > http://www.ko4bb.com/~bruce/IsolationAmplifiers.html
> >
> > Anyone has a number for this?
> >
> > I've tried googling it, but the results are mostly filled with the other
> > kind of iso amplifier where isolation refers to galvanic isolation.
> >
> > Regards,
> >
> > Stephan.
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