AW: [sdiy] power supply (un)symmetry

[René Schmitz]

Matthias Herrmann wrote:
> okay john,
> 79xx/78xx regulators don't seem to be the best choice!?

No, they are the 741 of power regulators. :-)

The LM317 and LM337 are a better choice, since you can trim these.

If you want yet lower drift you'd have to build something around a 
precision voltage reference. I.e. reference plus opamp (watch out for 
offset drift on these) and pass transistors.

Cheers,
  René


> -----Ursprüngliche Nachricht-----
> Von: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]Im Auftrag von John Luciani
> Gesendet: Donnerstag, 1. Juni 2006 22:18
> An: Matthias Herrmann
> Cc: Synth-Diy
> Betreff: Re: [sdiy] power supply (un)symmetry
> 
> 
> On 6/1/06, Matthias Herrmann <matthias.herrmann at fonik.de> wrote:
> 
> 
>>i recently built a little powersupply for the soundlab i am building. it
>>converts 9VAC to +9V/-9V DC and +12V/-12V CD (for the midi2cv converter).
>>its made out of four diodes, 4 polarized caps and some 78xx/79xx. actually
>>it is a mod of the doepfer A-100 miniNT bus.
>>unfortunately it is not 100% symmetric. actually it provides +9,2V/-8,8V
>>(+12V/-12V accordingly unsymmetric). i don't know whats wrong yet.
>>
>>i wonder if this would be critical?
>>and if so, how to fix it with few parts?
> 
> 
> It almost seems like there is problem in your power output ground since one
> supply is high by the same amount that the other is low. You may want to
> check
> for grounding problems.
> 
> A 2.5% error is probably within the output voltage specification of
> the regulators
> (check the Vo parameter in the datasheet). If you need higher accuracy
> you probably
> need a different design.
> 
> (* jcl *)
> 
> --
> http://www.luciani.org
> 
> 


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