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"new" Atari STFM / STE PSU design idea


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I did mention about this about a year ago, but due to costs, it wasn't really worth investing in a new design.. Though there is a possibility.

 

Currently, I am upgrading the Atari PSU with better caps etc, so that is essentially a new switchmode PSU. I saw little point in re-inventing that design. If that did happen, the pulse transformer would have to be re-used for starters to save huge costs, so it eventually just gets back onto updating the old PSU.

 

The cheaper option is just to use a toroidal transformer. Their efficiency is probably going to be better than the older Atari PSU's anyway and those things get pretty hot for starters. The easy solution would just be to use classic linear regulators, but those things are not good for transient power and get pretty hot. But with low cost switchmode designs in recent years, MHz switching power is available.

 

I have been spending a little time looking into switchmode designs. There are fully integrated solutions, but the down side is, they often need a fairly larger inductor to work. Which takes up a lot of board space, and can get fairly expensive. more complex designs (even though I was trying to avoid that) Generally use smaller inductors which are a lot easier to obtain. Generally these deisgns are just using a few resistors/capacitors, small inductor so the design isn't to bad overall space or cost wise. Choosing Mosfet's for these designs has to be done carefully also. Otherwise it results in the need of adding heatsinks etc which isn't what I would like to do. Space and cost etc again.

 

I have a design in mind and will be building this up anyway. As many know, my work on CPU boosters is really needing a stable PSU. I suspect the surge current when the floppy drive motor is turned on is dropping the rail voltage by about 1V (have mentioned all this before anyway) and causing the white border on the monitor to dim as the rail voltage sags. Some Atari PSU's are worse than others (even after upgrading them). The fact is, they are simply to slow to react to current demands. this really shouldn't happen, but it does. So a faster reacting design is what I would like to invest time in.

 

Most people will already be thinking "PicoPSU" but I really want to replace the Atari PCB with a better version. I am probably alone in not liking the PicoPSU stuff. I brought several of them over a year and and had nothing but problems with them. I paid various amounts, for various versions/designs from various suppliers and just had a mix of not working, or going up in smoke. I may have just be incredibly unlucky to have every single one faulty, but it has really put me off those things. In the end I brought a much larger 200watt (a few inches long) to power my CT60 on my falcon, and that worked out of the box no problems. I don't really like the idea of having a external PSU "brick" hanging out the back of the machine either. There may be other options but its not not for me. There are some small switchmodes boards out there, but I would rather design something myself that I know I can trust. Having had one of those brick type PSUs go faulty and output 50V for no reason, I really do not want to trust my hardware to such things.

 

Another problem is, do we really need 12V these days ? I don't know if anything actually use 12V anymore ? Not producing a 12V rail would save on cost a fair bit. Or a lower cost solution could be done for 12V as it is only rated 1A on the Atari PSU anyway. I am really aiming for about 5amps on the 5V rail to give it some headroom over the 3A Atari PSU.

 

So my PSU design will go ahead in the near future. I will just be etching out a PCB here myself (when I can dig out my PCB stuff!) As if people want to order one, well that would depend on demand and how much people would be willing to pay. It would require a small PCB run for that. I will post back here a image of the prototype when I get chance to build it :)

 

 

 

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Floppy drives need 12 V too - at least most of them. And I guess that load is some 500 mA Don't forget that most of Ataris is equipped with older drives.

I had only 1 , only 5 V powered floppy drive, and that was actually first one I bought in 1987 (Epson) :)

And serial port needs +12 and -12 V too . -12V is done with onboard TL497. Then, PAL Encoder and RF modulator use 12 V too .

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Your right about the 12V on the video side, Seems it pops up more than I thought.

 

I have a epson drive here, I checked on power connector and 12V isn't used. The Sony drives I always use now only ever needed 5V as I used them as external drives. What make / model drives do you have which need 12V ? I doubt I ever saw one here.

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Very interesting! I think it would be important to think about a target price first. Maybe a 50€ PSU on a 50 to 100€ machines...:S

 

Another thing is the Falcon/MSTE/TT...There, a 50€ PSU is OK because the machine is expensive.

 

Target price would be as low as possible ;) £50 would be about the figure easily. If it ends up being £60 -£70+ area then it would be to expensive. Though I am going to build up a prototype soon, so I can price up the parts as I go along better.

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Beats me. I do know this though, when I was using a Pico power supply, experimenting with replacing

that large, proprietary internal power supply board, I had everything working just fine - except for one

small item... the LCD. I never could get it to power up with the Pico. I am assuming the 2 are related

since I could not. I had a replacement screen working just fine, going through the external monitor

port on the STacy, just not the internal LCD. The Pico doesn't give a -20v anywhere, so I'm guessing

that was it.

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