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Post by dshadoff on Jun 14, 2020 22:05:48 GMT
I saw a YouTube video where somebody replaced his 7805 regulator and heatsink with a drop-in-replacement replacement based on a switching regulator. He had used this part: OKI-78SR-5/1.5-W36HE-C www.mouser.ca/ProductDetail/Murata-Power-Solutions/OKI-78SR-5-15-W36HE-C?qs=AQlKX63v8Ru%252BEtbp1ey3tw%3D%3DI have heard engineering discussions around switching supplies and regulators potentially adding noise because of the frequencies they use for voltage conversion, but the same discussions have also stated that this is controllable and shouldn't be detectable if care is taken in the design. The above module is designed as a drop-in replacement for the 7805 so it should have already taken these things into consideration; similarly, it is an encapsulated module so it is also likely intended for reduce EMI emissions. I was just wondering whether anybody has experiences with these types of modules, and whether they were good or bad (or whether any special considerations are needed in order to change it from bad to good). Right off the bat, I would be a bit concerned about the modules which are essentially exposed circuits, but I'm curious about the encapsulated modules.
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Post by apolloboy on Jun 27, 2020 9:39:01 GMT
I’ve tried these before and I always wound up going back to the 7805s, these just put out too much video interference. Even adding a filter cap between the output and ground didn’t help much.
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samiam
Punkic Cyborg
Posts: 100
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Post by samiam on Jun 27, 2020 10:07:37 GMT
If and when I try this on a particular white PCE I have, I'm going to go all out on filtering the output of the regulator. I'm thinking a few different types of decoupling capacitors as well as an inductor, plus extra decoupling capacitors added around the HuC6260.
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Post by dshadoff on Jun 27, 2020 16:10:10 GMT
I’ve tried these before and I always wound up going back to the 7805s, these just put out too much video interference. Even adding a filter cap between the output and ground didn’t help much. Which model(s) did you use ? I've seen many, and I think there would be a difference between, say, an exposed-board one from AliExpress and an encapsulated module from Murata (OKI). Even the various ones available from Mouser have differences on their datasheets, so it makes a difference.
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Post by dshadoff on Jun 27, 2020 16:12:03 GMT
If and when I try this on a particular white PCE I have, I'm going to go all out on filtering the output of the regulator. I'm thinking a few different types of decoupling capacitors as well as an inductor, plus extra decoupling capacitors added around the HuC6260. Sounds like a plan, but will you test at intermediate points ? Just a note - if there is interference, it doesn't need to be simply power-line interference; it could be EMI... which is why I'm particularly curious about the bare-board-versus-encapsulated module comparison.
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samiam
Punkic Cyborg
Posts: 100
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Post by samiam on Jul 4, 2020 7:42:38 GMT
After some consideration, I've decided to do the following:
- Use an external 5V SMPS - Completely leave out any voltage regulator in the system - Replace the power supply jack on the console with something different, and possibly uncommon, to prevent accidental connection of another power supply - Install an inductor (I think I'll try 10uH to start) across the points left by the 7805's input and output, and otherwise add a few ceramic capacitors of various values - Replace the 47uf electrolytic cap that decouples the 5V power rail right after the regulator with a 220uf OS-CON - Do the "jailbar fix" for the HuC6260 to keep that area extra stable
I might do so simply out of curiosity. The only way to design a universal noise filter is to have a particular 5V regulator be part of the design, since noise characteristics are going to be very different from one regulator to the next. I'm basically going to use whatever SMPS is available and outputs a true 5.0V (average), so I'm not particularly concerned with coming up with the simplest, cheapest solution.
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Post by dshadoff on Jul 8, 2020 23:22:39 GMT
I just re-read the above, and I don't think you want to put an inductor across input and output... maybe you mean putting it in series between the output of the regulator module, and the power rail of the device...
In other news, the OKI-78SR-5/1.5-W36HE-C reappeared in stock at Mouser, and I bought one and installed it in one of my CoreGrafx this afternoon. I powered it up, and... everything looks normal. No video noise that I can see, no particular audio noise. Looks like it should, as far as I can tell.
Having said this, I'm driving a Commodore 1701 13" monitor, so noise wouldn't be as obvious as it might be on a huge screen. But it's clean as far as I can tell.
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Post by dshadoff on Jul 12, 2020 4:41:52 GMT
I got a little more insight into this from a console modder on Twitter. He was telling me that certain consoles - such as NESRGB - were far more sensitive that others, and that the PC Engine has a well-designed power section so it's not much of a concern on the PC Engine.
This may give a little insight as to why there are conflicting views out there..
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