RE: LM31T as AC voltage regulator for Commodore computers PSU

That surprises me.....it seems like the most "commonly available" wall-warts these days use switching power supply circuitry..........maybe it differs by country?

-----Original Message-----
From: Clockmeister <clockmeister_at_internode.on.net> 
Sent: Saturday, June 18, 2022 8:51 PM
To: cbm-hackers_at_musoftware.de; tokafondo@tokafondo.name
Subject: Re: LM31T as AC voltage regulator for Commodore computers PSU

9VAC transformers are commonly available brand new in plug-packs 
(wall-warts) or as individual components from most electronics suppliers.



On 19/06/2022 5:17 am, tokafondo_at_tokafondo.name wrote:
> 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_at_tokafondo.name
>         <mailto:tokafondo_at_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
>
>
>