[sdiy] Bipolar PS with untapped xformer

[Oscar Salas]

It is similar to the mfos wallwart.

Regarding the transformer rating keep in mind that the same secondary is
providing the current for both rails.
In a configuration like mfos wallwart, when 125mA flow in the supply
output i measured 0.5A flowing in the transformer secondary.
This means that from a 0.5A transformer you can only output 125mA per rail.

I would use the common configurations using transformers with two
secondaries.

Maybe of your interest:
http://electro-music.com/forum/viewtopic.php?t=51694
Regarding the filter capacitor size, see last post in second page.

Oscar.

>> its really no different than the many AC (wallwart) TO DC projects out
>> there...correct ?
> Pretty much. This schematic is actually slightly more confusing in my
> opinion, but the advantage is it uses two of the same positive
> regulators. You can find similar designs by searching for bi-polar
> supplies using only positive regulators.
> My design of choice for single tapped transformers is essentially the
> MFOS wall-wart one. I'm by no means the authority, but I don't think
> all the 3300mF capacitors are necessary. I've used between
> 4700mF-2200mF, then something in the 47-22mF range, then a .1mF. I'm
> posting because I feel like being corrected if this is a bad idea.
> Never been a problem for me though. I would also add a .1mF on the
> output for some additional filtering. Again, just me.
> The beauty of doing it that way is it is simple to adapt for dual
> tapped transformers (same thing just two more diodes), and negative
> regulators are easy to identify and troubleshoot. It can be more
> difficult to figure out if you made a *gasp* mistake if using two
> positive regulators.
>
> --
> Nate King
> Paper Products Music
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