[XCSSA] Power Supplies Continued

[X-otic Computer Systems of San Antonio]

Alright I think I have this figured out! So, after reading up a bit on  
this stuff, while I haven't yet figured out a good purpose for having  
2 secondary outputs, having a center-tap makes total sense. I think  
I'm going to go for a 12VAC power supply though over the 10V. That's a  
bit more juice for the 7809 to handle, but the current draw should be  
much less then the +5VDC. 6VAC should give me some headroom for making  
sure the 7805 has enough voltage headroom so that it can properly  
rectify. I may have to bust out some actual math for that just to be  
sure though :)

This method vastly simplified my design, however. While I wasn't able  
to find a template for a center-tap transformer in Eagle, I opted to  
omit it entirely from the board. Instead, I put pin headers that I  
will connect the wires from the transformer to. No real need to mount  
it on a PCB if I can just mount it to whatever container I house all  
this in, after all (though I still need to work out the details for  
that).

One more question, though :) Where should I put the fuses for the DC  
output? Should it go right before the DC output pins (which is where I  
have them now), before the rectifier, or right after the transformer?

Thanks again! This has been most helpful!

Tim S.

On Dec 27, 2008, at 7:11 PM, X-otic Computer Systems of San Antonio  
wrote:

> Hmmm...I was actually sort of thinking something similar. Now this one
> has a center tap, but would the same thing work if I had a standard
> multi-tap (1 primary, 2 secondary)? Either way, how exactly does one
> hook this up to do that? I've read that you can double the voltage if
> you hook it up a certain way, but I thought it was one or the other?
> In other words, I couldn't tap off one secondary (say to get 5V) and
> both secondaries (to get 10V) at the same time? I'm not sure if my
> explanation is even correct but hopefully it's enough? :) I'm trying
> to find the data sheet I saw the different hookups on still but, of
> course, I can't find it when I need it :P
>
> Sounds like this might work out well though! The only thing I'd need
> to work out would be how much DC voltage I'll end up with in various
> configurations. The specs on the 78xx call for providing 1-2V above
> what it is going to regulate, but I'm not sure how that translates
> with AC. I know that AC output depends on load, etc. but I've never
> gotten a clear explanation of what type of AC adapter to use in order
> to properly regulate the result?
>
> Thanks again!
>
> On Dec 27, 2008, at 6:53 PM, X-otic Computer Systems of San Antonio
> wrote:
>
>> Tim,
>>
>> What about something like this,
>> http://www.mouser.com/Search/Refine.aspx?Keyword=546-187E10
>> The secondary is 10VAC with a Center Tap.
>> That should give you 10 and 5 VAC...
>>
>> /Fredrik
>>
>> X-otic Computer Systems of San Antonio wrote:
>>> If I could find a clean one, that might work. Trouble is, most
>>> switched power supplies are quite noisy for analog audio
>>> applications.
>>> The SIDs are analog devices and so require very clean power. To be
>>> fair, I've used some nasty DC power supplies and things worked out -
>>> the smoothing capacitors did their job, but I think converting AC to
>>> DC oneself tends to be the better route to go. That way you know how
>>> it's made, etc.
>>>
>>> That's one reason I'm trying to avoid using multiple voltage
>>> regulators in fact. Supposedly, chaining regulators adds noise as
>>> well, so if I can use a single regulator for each output that might
>>> result in a nicely quiet solution. I think I may end up going with
>>> two
>>> transformers ultimately. Finding a multi-tap that can output
>>> something
>>> close to 5 and 9VAC seems to be somewhat difficult.
>>>
>>> Decisions decisions! :)
>>>
>>>
>>> On Dec 27, 2008, at 5:41 PM, X-otic Computer Systems of San Antonio
>>> wrote:
>>>
>>>
>>>> Perhaps you might consider using two modular DC switching supplies
>>>> (5V/1A & 9V/300mA) that have regulators and over-voltage protection
>>>> built-in?
>>>>
>>>> You could mount the two supplies in a hobbist handy box, and add
>>>> an on/off switch and input fuse for the 120VAC line.
>>>>
>>>> Lou
>>>>
>>>>
>>>>
>>>>
>>>>
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>>
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