# Re: 9VAC from 5VDC?

From: Jim Brain <brain_at_jbrain.com>
Date: Sat, 14 Sep 2013 01:06:15 -0500
Message-ID: <5233FCD7.1010706@jbrain.com>
```On 9/14/2013 12:43 AM, john/lori wrote:
> Jim Brain wrote:
>>
>> That's fine, but I do think I can provide a pretty nice sine wave
>> approximation to the transformer.  Either way, my sticking point is
>> the transformer selection.  Any links to a suitable offering?
>>
>>       Message was sent through the cbm-hackers mailing list
>>
>
> The advantage of doing the DC > AC after bumping up the voltage
> is that you can run the voltage converter at a much higher
> frequency and use a much smaller transformer.
> Also voltage drops will be a smaller percentage (if you're
> doing eg PWM)
I understand, but at some point, I'm just designing a PSU.  I see lots
of 5VDC @ 60W or 80W PSUs online for cheap, and anyone can buy one.
That takes care of one voltage, if I the circuit can make the other.
And the PSUs are CE and UL-listed, or at least some are, and they are
switchers, so they can be plugged into anything 90V to 260V.

>
> How'd you get 5 Amps ?
9VAC RMS @ 1VA = 12.73V Peak @ 1A.

Creating that from a single side PSU will require ~25VDC @ 1A

That's 25W

That's 5A @ 5V

If I do as Bil suggests, and use a center tapped Xformer, then the
voltage need only be 12.5V @ 1A for each half cycle, or 12.5W which is 2.5A

Maybe it's 2.5A regardless, but AC is not my strong suit.

Jim

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```