[sdiy] 5V power supply for logic and uC

[Barry Klein]

I say buy a surplus 5V 1W or better wall adapter.  Enjoy its switching noise
intermodulating with that of the HDD's switching converters.  :-)
It adds to the digital ambiance.
If those HDD's can work with switchers and the miniscule head signals they
deal with surely your synth circuits will be fine.

Like the recent Elektor article describes, switching converters have taken
over.  Linears are mainly used for low current LDO functions.
The heat from linears is more damaging to your synth circuits than radiated
noise from switchers - if you take care in converter choice, placement, and
layout.
I have to test converters in my job.  Some of them are of old design and
have some issues but the newer ones are pretty awesome.  The circuits
providing multiple watts run cool, with little noise, are very efficient,
and have very low parts count.  They tolerate constant shorts without damage
and some have pretty high input voltage range.

I don't want to start a war on this topic - just saying the new parts are
pretty nice and you will find them in most synths going forward.
Jeez, maybe this is why soft-synths can't cut it?  :-)  Heck, forget both -
use tubes.

Oh, and on your modules - use proper bypassing techniques for your digital
circuits.  This means you may have some low esr bulk capacitance at the
supply input but also be sure to have high frequency suppression ceramics at
the chips themselves.  Possibly add ferrite beads on chip VCC inputs too.

Another thing, if 5V is not normally supplied with commercial synth case
systems it indicates you want local 5V sourcing off the 12V on each module.
Otherwise, let's say your module works awesomely and you want to make and
sell a bunch.  No 5V on your customer's system...

Barry


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of ChristianH
Sent: Friday, November 02, 2012 02:44
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] 5V power supply for logic and uC

On Fri, 2 Nov 2012 09:01:18 +0100 Mattias Rickardsson <mr at analogue.org>
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? Do you have lots of hard disk drives in your synth sucking from
the +12V?
Usually, bipolar power supplies are used for opamps etc., I wouldn't
expect significant asymmetric loading here.

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

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. It wouldn't matter if it gets some spikes from a microcontroller
or from some VCO reset surges.
If I need a reference, I usually pop in a cheap LM336, or if I'm feeling
generous an LT something. And add some filtering to it.

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

Chris



> On 1 November 2012 18:40, Thomas Strathmann <thomas at pdp7.org> wrote:
> > Hi all,
> >
> > I'm planning a number of modules that will need a 5V supply to power
> > logic ICs and microcontrollers from the 12V rail of a Doepfer modular.
> > What I'd like to know is what measures I should take to protect the rest
> > of the modular from noise. What I'd do at this stage is just add a 7805
> > voltage regulator with the standard caps from input and output to GND.
> > Is this a recommended approach or is there a problem with this?
> >
> >         Thomas

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