Brainstorming to design AC-HBx power supplies

By mcolom

Champion (311)

mcolom's picture

28-01-2023, 21:57

Hi all!

As you know, Sony HB computers use the AC-HB1, AC-HB2, and AC-HB3 power supply units, which have a proprietary non-standard connector to the MSX. It's possible to modify the machines to power them with USB, but it'd be better to have a replacement from the original power supplies.

In the wiki we have the schematic, which is quite simply: a center-tap transformer with two diodes and a capacitor to filter the oscillations.

I'd like to know about your thoughts about designing an alternative, kind of a brainstorming.
Is there already a valid alternative? If there isn't, why?

If I had to design the thing, I'd consider:
- Safety: it should be completely safe, and not to arc and set everything on fire, or electrocute anyone Smile
Also, I've seen that some transformers come with a note such as "This product can expose you to chemicals including Di(2-ethylhexyl)phthalate (DEHP) which is known to the State of California to cause cancer". Since we'd be at the design phase, obviously we should discard those. The question is whether other transformers have DEHP or similar and we could be unaware.
- Should be use a real center-tap transformer, or a modern switching one? Switching regulators might introduce some periodic noise that could affect the video signal, I've understood.
- We should also include a fuse, which I'm not sure the original unit has.
- We should also have the AC current along with the DC 9 V. Most MSX work without the AC (it seems it's only used by some special cartridges), but in this design we should include it, unless it affects safety, because of component availability, or if increases the price too much.
- How to build the connector? With a 3D-printer, I guess. Would that be enough? Or are better alternatives?
- Are the 3 pins in the connector a known model available today? Which one? Otherwise, any alternative?

The new power units will be also quite useful in Europe if we don't have to make a tower of transformers for Japanese MSXs working at 100 V. We could make the input directly 220 V.

Well, for sure there will be more considerations to take into account, but I'd be happy to read your opinions!

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By mcolom

Champion (311)

mcolom's picture

04-02-2023, 18:45

I've created a project in Github for it, where I'll try to gather all the information I can about how to build it: https://github.com/mcolom/AC-HB3_rep
If you have any new information, or if you want to contribute, don't hesitate! Pull requests or even discussions in the Issues are very welcome.

By gdx

Enlighted (6112)

gdx's picture

05-02-2023, 01:00

By mcolom

Champion (311)

mcolom's picture

05-02-2023, 10:28

Thanks! I've added it to the README.md, along with the other relevant thread. And a nice video of Ben Eater on switching to increase voltage.