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-   -   Developing a new A500/1200/600 power supply. -12V needed? (http://eab.abime.net/showthread.php?t=79361)

Mounty 10 August 2015 11:59

Developing a new A500/1200/600 power supply. -12V needed?
 
Hi,

I am in the early stages of developing a new power supply for the A1200/A500/A600.

Instead of going for the multi-box/adapter approach, I am developing a single-box solution.

I am going for a colour-co-ordinated enclosure with a status LED. This would look better than an ATX psu I think, and would not need an adapter.

The thing is, it would be significantly cheaper if I left out the minus 12 volt line. This is only used for RS232 comms (null modem connections etc).

What are your feelings on this? Can we live without RS232?

Tmw2n 10 August 2015 13:06

Could you not stick in an LM7915CT and associated gubbins and get -12V that way? should add less than a pound to parts cost of the psu, and -12V shouldn't need more than an amp I'd expect.

Mounty 10 August 2015 13:10

About 100mA.

I wouldn't use a LM7915CT the losses would be too high. Instead I would use a MC34063ABN-based circuit.

It's the gubbins that makes all the difference, you'd be suprised what a few mosfets, inductors, electrolytics etc adds up to.

But why bother if no-one needs it?

ajk 10 August 2015 13:21

I think it also goes to the expansion connector on the A1200 at least, not sure if any expansion uses it though.

How about designing it into the PCB, but not populating the components unless someone really needs it?

robinsonb5 10 August 2015 13:33

Doesn't the audio circuitry need -12v?

john1979 10 August 2015 14:15

Yes I believe so. I once forgot to connect -12 when converting my ATX power supply and there was no audio.

Retrofan 10 August 2015 14:16

No idea about the -12v line, but I need exactly 5volts delivered to the psu plug of the Amiga. Jens was going to put a sensor there to control it.

Daedalus 10 August 2015 14:35

Yes, -12V is also needed for audio. It'll still work without it but will be totally distorted. I can't imagine any expansions used it, but the fact that it was on the expansion connector allowed the Mediator board and similar to power the computer (including -12V line) without connecting anything else to the motherboard.

duga 10 August 2015 14:42

You need -12 V for both serial and sound AFAIK.

Akira 10 August 2015 16:30

Yup, as said before, -12V is essential to audio.

Locutus 10 August 2015 16:35

yup, -12 will be needed to drive opamps, so audio :-)

hese 10 August 2015 17:43

-12V is needed... just in case it was still unclear. :D

BarryB 10 August 2015 17:45

Be nice if you could make it both Amiga/C64 compatible :great

Mounty 10 August 2015 20:12

Fair enough if the audio needs it, it has to be there, no question.

I'll look into C64 compatability. Shouldn't think that will be a biggy. Unless it needs minus 5v..

Akira 10 August 2015 20:22

Quote:

Originally Posted by Mounty (Post 1035361)
I'll look into C64 compatability. Shouldn't think that will be a biggy. Unless it needs minus 5v..

You also need 12 or 9V AC for a C64 (12V for old ones, 9V for new ones). I wouldn't bother trying.
I think your main problem here would be to get the square DIN connector. Other than that, it's a pretty standard power supply.

Mounty 10 August 2015 20:43

Quote:

Originally Posted by Akira (Post 1035362)
You also need 12 or 9V AC for a C64 (12V for old ones, 9V for new ones). I wouldn't bother trying.
I think your main problem here would be to get the square DIN connector. Other than that, it's a pretty standard power supply.

Square? I thought the C64 used a round connector.

You're right though, it doesn't look practical to build in C64 compatability.

Akira 10 August 2015 21:25

Quote:

Originally Posted by Mounty (Post 1035369)
Square? I thought the C64 used a round connector.

The AMIGA has a square DIN connector and this will be your problem.

Mounty 10 August 2015 21:31

Quote:

Originally Posted by Akira (Post 1035381)
The AMIGA has a square DIN connector and this will be your problem.

I may have a supplier for this connector, but if that does not happen, then the buyer would need to transfer the cable from his broken psu.

I think everyone expects that anyway. It's widely known these connectors are extremely difficult to source.

Retrofan 10 August 2015 21:39

Yes, two seconds to find them http://www.vesalia.de/r50e_amiga_har...pare_parts.htm

It would be nice if you could make a Mechy Apower style PSU.

To make it unbeatable it would have to add the 5v sensor in the power connector to supply exactly that.

BarryB 10 August 2015 21:59

If no C64 support, build one separate. A few members have looked into making one, even Jens, but no one so far has done it and released one :(

As for the square plug, it was made by Mouser Electronics, Stock No. 171-4405


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