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uC3842AN SMPS idea for feedback - What do you think?
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MagicSmoker:

--- Quote from: WyverntekGameRepairs on December 14, 2019, 10:53:15 pm ---Hm. You know what, you've got a point there. I think I've heard of this technique before, something like primary-side feedback? It omits the opto and replaces it instead with a coil on the transformer. And that also means less parts so less points of failure, so that could actually be a fantastic idea. Would there be any important aspects I would need to consider if I was to use this method?
--- End quote ---

As T3sl4co1l already mentioned, the higher the leakage inductance the worse the cross-regulation. Still, if you can keep leakage under 3-4% (which is eminently reasonable, even with all the safety agency mandated crap) and the loading of the outputs doesn't vary too wildly this technique works well enough. Don't let perfect be the enemy of the good and all that. However, this technique should only be used on flyback converters, not forward types.

And yes, you are going to need a custom transformer here, but that was always the case because the only SMPS transformers you can buy off the shelf are overpriced jobs intended for dev kits and reference designs. The chance you will find one that fits your design specs is somewhere between nil and none.

EDIT - posted before including the other part of the reply:


--- Quote from: T3sl4co1l on December 14, 2019, 11:09:23 pm ---You'll be lucky if China can make it for that price in quantity, let alone in small quantities, let alone in the US.  If you're selling hundreds/year I would guess $200 would be closer to profitable, assuming of course you get that many buyers at that price.
--- End quote ---

Aye, this is undoubtedly a questionable business venture, but that doesn't mean it isn't a worthwhile endeavor for the OP to undertake. You really don't learn the intricacies of product development until you've actually developed a product, after all.

WyverntekGameRepairs:

--- Quote from: MagicSmoker on December 14, 2019, 11:48:02 pm ---
--- Quote from: WyverntekGameRepairs on December 14, 2019, 10:53:15 pm ---Hm. You know what, you've got a point there. I think I've heard of this technique before, something like primary-side feedback? It omits the opto and replaces it instead with a coil on the transformer. And that also means less parts so less points of failure, so that could actually be a fantastic idea. Would there be any important aspects I would need to consider if I was to use this method?
--- End quote ---

As T3sl4co1l already mentioned, the higher the leakage inductance the worse the cross-regulation. Still, if you can keep leakage under 3-4% (which is eminently reasonable, even with all the safety agency mandated crap) and the loading of the outputs doesn't vary too wildly this technique works well enough. Don't let perfect be the enemy of the good and all that. However, this technique should only be used on flyback converters, not forward types.

And yes, you are going to need a custom transformer here, but that was always the case because the only SMPS transformers you can buy off the shelf are overpriced jobs intended for dev kits and reference designs. The chance you will find one that fits your design specs is somewhere between nil and none.

--- End quote ---

That's quite a bit to take in. You've got a point, too, perfection isn't everything. I just want it to be as functionally stable as possible is all. And yes, leakage inductance. That's going to be an assfest to deal with, especially if I tried using an off-the-shelf part. I think the reason I was leaning toward using an opto in the first place is because that is how the transformer that I was designing this around is built for.
The transformer had the right specs and everything, and it was designed specifically for the uC3842AN. It has the correct outputs, it has the correct safety regulatory specs, it has everything I need. It's when better concepts are introduced that I start getting frustrated, because the transformer I want probably doesn't have said feature.

Switch mode power supplies are not complex. They are big systems made of elementary circuits, and so they have many moving parts. Each moving part does something with precision. Then you have a design, but you have improvements but cannot make said improvements because certain parts cannot be changed, then one must compromise. I might have to forget about primary-side feedback. Unless... I might be able to stack transformers. Problem is, this might affect leakage inductance greatly.

I'm at a loss right now.  |O :scared:
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