[sdiy] Adapting exponential convertor for single supply

[Michael E Caloroso]

There's a lot of compromises (and gotchas) with single supply opamp
circuits.  It isn't as simple as bias and virtual grounds.

Look for these app notes:
Maxim Integrated AN656 "Design Trade-offs with Single Supply Opamps"
Analog Devices "Designing Single Supply Low Power Systems"
Microchip AN682 "Using Single Supply Opamps in Embedded Systems"
TI SLOA030A "Single Supply Opamp Design Techniques"
TO SLYT189 "Single Supply Opamp Design"

I highly doubt that the OTA will work in a single supply scheme with
the negative power pin at ground.

MC

On 7/26/17, Scott Gravenhorst <music.maker at gte.net> wrote:
>
> Oren Leavitt <obl64 at ix.netcom.com> wrote:
>>I would go with the midpoint derived "ground". It seems to me that would
>>guarantee proper current sourced into the control pin of the LM13600
>>
>>- O
>
> Also make sure that when you use this circuit, the ground used to reference
> signals is
> the _virtual_ground_ and not the -v supply pin.
>
> Also please understand that a virtual ground is anything but "good".  It is
> a
> technique that is useful in small circuits where almost NO current is either
> sunk or
> sourced from "ground".  It is also susceptible to noise propagation, so do
> due
> diligence in suppression of noise in the part of the circuit that creates to
> virtual
> ground.  An opamp can help to fortify the virtual ground.
>
> My main point here is that I've seen too often an attempt to do a single
> supply thing
> (why? supplies, especially for small stuff are not expensive) resulting in
> non-working
> crap because of the temptation to use the negative side of the single supply
> as the
> ground instead of the virtual ground.  Virtual grounds also introduce
> variables that
> you really don't want to have to chase.
>
> My opinion on single supply stuff to mimic what dual supplies do - don't.
> just don't.
>
>>
>>
>>On 7/26/17 5:31 PM, Tom Wiltshire wrote:
>>> Hi All,
>>>
>>> What’s the simplest way to adapt this exponential convertor
>>for a single supply (0-9V)? > > http://imgur.com/ZhixiC7 > >
>>Could I use a simple midpoint bias to act as the ground and
>>expect it to work? It feels wrong, although I don’t know why. >
>>Bumping the “grounds” up to a useful level with diodes feels
>>better somehow, more like is done in this schematic: > >
>>https://hackadaycom.files.wordpress.com/2015/09/two_transistors_expo-sch.png
>>
>>> > What would you recommend? > > Thanks, > Tom > >
>>================== > Electric Druid > Synth & Stompbox DIY >
>>================== > > >
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> -- ScottG
> ________________________________________________________________________
> -- Scott Gravenhorst
> -- http://scott.joviansynth.com/
> -- When the going gets tough, the tough use the command line.
> -- Matt 21:22
>
>