[sdiy] Equation question

[Justin Owen]

> When voltage - or a percentage of voltage (i.e VCC2) - is used as part of an equation in a single supply circuit, then
> Voltage (obviously) = Voltage. 
>
>When using a bipolar supply (i.e. +/- 12 Volt) is total voltage (or say, a third of the supply voltage) calculated using 12V
>or 24V? 


>If I understand the question, it depends on the reference.  
<edit>
> - in this case it isn't, it's the negative rail.

Thanks Scott and David,

So - for an op amp that has V+ supplied by +12 Volts and V- supplied by -12 Volts - would an equation that refers to 'a third of the supply Voltage' be talking about 12 or 24 Volts?

This is the first time I'll be using an op-amp under dual supply - I could just plug it all in and see what happens (which is what I normally do...) but I thought it might be interesting to try and calculate/predict some results.

Sorry if I'm asking how long a piece of wire is...

Cheers,

Justin