[sdiy] Adapting exponential convertor for single supply

[rsdio at audiobanshee.com]

Along the lines of what Scott is suggesting, there are supply chips which can create a negative voltage from a positive voltage. So, your 0-9V unipolar supply could turn into a +/-9V supply. Varying amount of current are possible, and while the inductors needed might introduce noise, there are ways to filter that out.

In other words, you might find it easier to just add one chip with a few support components and then follow the bipolar circuit examples that you already have for everything else.

Brian


On Jul 26, 2017, at 7:28 PM, 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 > > 
>