[sdiy] Jürgen Haible living VCO core

[Neil Johnson]

[Protection diode in expo converter]

> > Not an issue if you're just tinkering on the bench, but for a commercial
> > product it's just lazy/bad design.
>
> Thanks - this is a point I'd not thought of: just because it
> (probably) won't damage anything right away, if it's outside the
> intended operating conditions it may degrade over time. I don't recall
> seeing a diode like that in any expo converter I've looked at. But I
> shall keep an eye out and include one in whatever I build.

Grab a copy of Franco's "Design with Operational Amplifiers and Analog
Integrated Circuits".  In my international edition section 12.4
discusses a practical log amp and includes a diode to prevent the
reverse biasing of the LM394 base-emitter junctions causing damage or
degradation.

Neil