Re: 9VAC from 5VDC?

On 9/13/2013 8:25 PM, john/lori wrote:
>
> Magnetics are traditionally black magic, but transformers aren'
> all that hard.
>
> I assume you're talking 5VDC so you want a transformer that's
> more like 2.6 : 1 (9VAC is 12.73 peak)
I'd be happy with 1:2 (yes, it'd be a bit low, but it would work for the 
things in the machine that care (sine wave for TOD, 9V unregulated which 
is turned into 6.2V for Cassette.  What, about 8V RMS at the user port, 
I'd be OK with that.

>
> Assuming you're dead set against just using a 9VAC wallwart or
> something next to your 5VDC, I think I'd try 5VDC to ~ +-13VDC
> then synthesize the 9VAC from that.
>
> The cheap inverters use a wave form something like this.
>
>    _       _       _
>  _| |_   _| |_   _| |_
> |     |_|     |_|
I can do a good sine wave with a uC.  No worries there.
>
> If you were going to wind your own transformer you could give it
> more steps.
I want something I can buy, as I assume, if this works, lots of people 
with dodgy PSUs will want to replicate it.  I could double/triple the 
voltage using a doubler/tripler and use a 1:1 isolation if needed, if a 
1:1 was easily sourceable, and a 1:2 was not, but that's more components 
and more things to solder up incorrectly.

So, a nice 1:2 or 1:3 transformer that will work in the use case would 
be ideal, something I can buy off the shelf.

Jim

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