[sdiy] 5V power supply for logic and uC

[Mattias Rickardsson]

On 2 November 2012 10:43, ChristianH <chris at chrismusic.de> wrote:
>
>> It feels like it might be a good idea to use the -12 V rail instead,
>> with some inverting switching regulator - both to minimize the lost
>> power and to avoid drawing current from the +12 V rail, which is more
>> likely to be heavier loaded than the -12 V already.
>
> Howzat?
> Usually, bipolar power supplies are used for opamps etc., I wouldn't
> expect significant asymmetric loading here.

Exactly, but everything else that is *not* using a symmetric supply
tends to sit on the plus side more often. For example CV
potentiometers, misc discrete circuitry, LEDs...

> However, having an avoidable switched DC-DC converter screaming in a
> synth circuit makes me shudder.

Me too. :-)

> I do see the point of using +12V for local references, but if you start
> calling something a reference voltage you better not use raw +12V for it
> anyway.

People do.

I was referring to "reference voltage" as in a non-zero voltage that
is used in a way that its exact and/or constant value is critical for
the circuit to work as intended. Such as the comparator voltage in the
reset circuitry of a VCO or the voltage connected to the frequency pot
of a VCF. Using a voltage reference is the is the least you could
expect from a serious and robust design, but I'd bet that around 99%
of all such voltages in all analog synths out there are taken directly
from the supplies, not from a voltage reference. :-)

> Call me old fashioned, but in the case mentioned I'd add a +5V PSU.

I'd rather call you quite wise. :-)

/mr