Re: Building a custom power supply

"andyavast" wrote ...

Scott Dorsey wrote:

andyavast wrote:
>Hello.
> I am looking for informed advice (and opinion) on an electronics
>project. I want to build the following:
>
>A power supply with 8no. 9VDC outlets supplying 1200mA (total, not >per
>outlet) and 1no. 12VAC outlet supplying 500mA.
>
>the supply is to fit into a hammond aluminium enclosure >approximately
>120mm x 60mm x 60mm perhaps a little bigger. My initial (if somewhat
>uninformed) thoughts are to use two seperate chassis mount >transformers
>with a full-bridge rectifier to convert the AC power to DC for the >9VDC
>outlets. Inspiration is what i need. Any ideas would be really
>appreciated.


Well, you need to know first of all that if you have a 12V transformer
producing 12VAC that when you rectify it you will get 12*1.4= 16.8V.

If you are going to regulate it afterward, this is fine. You just use
one 12V transformer and regulate the 16.8VDC down to 12V and 9V with
7809 and 7812 regulator chips.

There is a good introduction to linear supply design in the ARRL Radio
Amateur's Handbook.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

thankyou scott! i will look into the literature you suggest.Has anyone
ever designed simple linear power supplies of a similar nature to the
one i wish to build?

Sure, no deep magic involved. Note that Mr. Dorsey
may have mis-read you requerements to want 12V DC
and not 12V AC. A single 12V transformer could source
both 12VAC and 9VDC (after rectification, filtering, and
regulation).

NOTE HOWEVER that if you are trying to power a bunch
of small gadgets with this thing (the kind that would otherwise
use individual wall-warts), you may have a SHOWSTOPPER
problem with the interaction between what each of them
perceives as their own "ground" reference. Unless all
your loads for 9V are identical devices AND you know
the internal wiring (which side is "ground", etc.) you may
not be able to do what you are seeking.

Likewise, using the same transformer for the 12V AC output
is also potentially a problem when you try to create the 9V
DC from the same source.

While building this is not really that difficult, making sure
that it will work properly with all you loads is a very
different matter. I would urge significant caution.

.

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