[sdiy] 5V power supply for logic and uC

[Mattias Rickardsson]

One potential drawback is the amount of power that gets lost in the
regulation from 12 V. For every 5 W you pull out of the 5 V regulator,
12 W will be drawn from the 12 V rail. The remaining 7 W just becomes
heat in the 5 V regulator. In other words, the 12 V rail will have to
deliver much more power than you need.

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. A side-effect
could be that the +12 V rail gets less noise than the -12 V rail. The
+12 V rail is more likely to be used by some modules as some kind of
reference voltage.

On the other hand, a switching regulator can introduce new problems
hitherto unknown to man... ;-)

/mr

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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