Re: LM31T as AC voltage regulator for Commodore computers PSU

I will only say that this is an actual Commodore (and retro computers) desert. And most 9V adapters I've ever seen are from xDSL routers, AP and modems, long ago discarded.
18 de junio de 2022 22:12, "Mike Stein" <mhs.stein_at_gmail.com (mailto:mhs.stein_at_gmail.com?to=%22Mike%20Stein%22%20<mhs.stein@gmail.com>)> escribió:
Well, he's in Spain and you're in Italy; maybe you treasure the old traditional ways more than he ;-)

I don't know offhand how constant the 9V load of a C64 is but I would think that a carefully selected resistor with maybe a couple of Zeners to clamp any overvoltage might do the trick.

m 
On Sat, Jun 18, 2022 at 2:27 PM Francesco Messineo <francesco.messineo_at_gmail.com (mailto:francesco.messineo_at_gmail.com)> wrote: On Sat, Jun 18, 2022 at 5:42 PM <tokafondo@tokafondo.name (mailto:tokafondo@tokafondo.name)> wrote:
>
> TI's version of the LM317T's datasheet has something interesting to see in its page 15.
>
> It can be seen only in TI's datasheet, and not others AFAIK.
>
> They show how to use two LM317T IC in a way that from a 12VAC source, take it down to 6VAC. I'm sure that with changing the values of the resistors needed, 9VAC can be got, instead of the 6VAC of the example.

it is actually AC in the sense that there will be alternating polarity
voltages, however that circuit will clamp the waveform voltage to 9V
(or whatever you chose) as long as the input voltage is greater than
the set voltage. So you'll get a kind of "flat-top" waveform.
I'd say it's not ideal (it adds high frequency harmonics, both LM317
need to be heatsinked...)
I have never had any difficulty in finding 9VAC transformers.

Frank IZ8DWF