Flyback transformers, small, high power, where?

The HV winding could be wound as a preformed subassembly, possibly using simple VPI of a polyester resin. To allow for bake-out, I think you'd be looking at removable teflon, or teflon-coated forms.

As there's probably no room for interleaving, the same could be done for the secondary, in a side-by side arrangement, separated by a suitable foil layer extending through the part, unbroken in the immediate area of the coils.

Core material is a stumper. If ferrite dust composites can be made, then maybe same thing would be possible with amorphous crystaline dust. Basically already do that with iron dust and other materials.

If the amorphous HF losses were less than an order of magnitude greater than ferrite, at the temperature limit, it might be possible to cojole a permeability out of one mix so as to approach that needed. I think the loss/volume relationship of amorphous base material is actually worse than that, though.

There are physical limits to the amount of filler you can force into organic binders that have a suitable temperature index and flammability rating. I'm not sure about the insulation characteristics that would result, either.

Anyways, if the coils and their terminations were imbedded in a suitable block of the mix, using HPInjection molding, you'd be getting close to practical limits for the volume available. It'd still get hot, but I've seen SMD magnetics, with >70degree rises, paraded in the literature without apparently raising an eyebrow.

You wanting a 20W flyback transformer but wanting it in a small form factor is the big joke here. How many HV designs have you done? Try one negative 10W supply and one positive 10W supply and tie their returns together. So two flybacks to achieve the power density you are after. Two smaller form factor devices would fit your profile and likely allow for off the shelf sourcing.

Something to think about.

For me those are actually the most fun jobs. When it gets tough.

Lots of cutting edge projects can't be done incrementally at all, one must start completely fresh. Here is one example:

Yes, there are five ICs in that thing. And 64 sensors. This was definitely deemed impossible in the ultrasound world, and then we started producing hundreds of these per day. They save lives.

Well, that's flexible. Of course you always want to be able to regulate out surges but if the magnetics don't have enough oomph one may have to cut conversion.

Why wouldn't it?

I know but nowadays one can make rather thin-walled bobbins. Almost like film.

One can always thermally couple to the walls, that wouldn't be a problem. Not great, but man's gotta do what man's gotta do, as John Wayne said :-)

Thanks. It's a regular boost-mode chip though. Maybe it can be used as flyback, should be possible. LTC doesn't have to offer much in that area, AFAICT only up to 300kHz but at least that's a factor of three versus they flyback-PFC chips. And the voltage control in those isn't too great, would have to roll my own anyhow.

So yeah, that may be an idea. But first I want to find out what it takes to get a xfmr that can be run under 150kHz.

These two have been obsoleted.

App note DER-286 for the LNK419 is interesting. If their web site just wasn't such a mess. The only way to quickly get to their datasheets is via Digikey.

But the main show stopper for the LNK4xx series is the switching frequency. Much lower than for the LTC parts,

This is exactly the reason for my post, to see if there's any new miracle material. Looking at High-Flux and stuff, maybe there is.

Got to be careful with organic binder. There have been disintegration issues in the past, after a few years of service.

Do you remember which literature that was in? Most of what I found was in magazines such as "Power Electronics Technology", like this paper:

This one I didn't understand :-)

ROTFLMAO!

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Oxymoron?

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Maybe you should push the frequency up and deal with the EMI. Slow the edges down a bit and give up a little efficiency.

GF Nylon is glass in an organic binder, as are most bobbin materials. Magnetic composite aging is more an issue because they're self-heating with generally positive tempco of loss. And they can all be misused....

You may be in luck here, though links to such are not something I bother to save, if in electronic format. These generally expire too soon to be of any lasting use.

Following one of your own links yesterday, resulted in a pop-up for one example of magnetics rises of this order:

They're not uncommon, but you have to have your eyes open, before an eybrow is likely to also rise.

RL

If I see a really good publication on the web I store the whole thing, usually either in HTML or PDF. Very small price to pay. A few hundred kB of hard drive space is really nothing these days compared to the usual

Yup, nothing can beat a FLIR camera when it comes to power supply loss determination.

That is option #2, once we've determined that no "stretch-limo" version of a suitable E-core can be had or custom made. A few manufacturer answers are still pending there.

Upping the frequency is technically easy but there are no flyback-PFC chips that go above 150kHz, AFAICT. Then we may be looking at an off-label use of a boost-PFC chip. A bit of a white-knuckle ride because unless it's LTC it can't really be simulated, and LTC's boost-PFC chip only goes to 300kHz.

Why cling on to LTSpice? You could model the transformer and drive circuitry any way you like. IMHO the biggest problem will be finding a high voltage MOSFET which can be switched fast enough and there is the leakage inductance.

You can't do a full-blown SPICE analysis of the whole thing unless there is a useful behavioral model. LTC has fairly good behavioral models whereas other companies' models simulate every nook and cranny of a chip, meaning just a few runs with ramp-up plus some simulated event can take half a day. LTSpice is a major design help these days but, of course, they kept the real modeling tricks to themselves.

I have to simulate events that take many seconds. With a switcher that is quite painful in regular SPICE.

Those are the least of my concerns. Done it many times. You just have to make sure the spikes always stay well below 70% of abs max and you don't dissipate much heat due to spike muffling.

I never simulate an entire SMPS. I just simulate whether the voltages and currents aren't going crazy under several conditions and to get a ball park on how much snubbing is required. Because there is always a difference between te real world and the simulation I just make a small PCB and measure & tune a real circuit before committing it to a 'final' PCB.

I have to follow a different philosophy most of the time. Often my switchers go straight form the simulator to CAD, then layout. I must simulate "in the system", meaning load changes, loop stability, input surges and stuff like that. Occasionally the sim schematic already looks like a family size pizza.

not worth considering, if two 10W "transformers" will do the job, you just need to wire them in series-parallel for a 20W converter,

the problem with fllyback is the "transformer" is really a coupled inductor as it's an energy storage device and thus needs to be larger than the transformer in a similarly rated forwards converter.

There's another issue here. That GF Nylon example refers to filled nylon at 5, 10 or maybe 15% filler by mass/volume. There are distinct limits before the compound loses important physical properties that permit it's use.

To maintain useful magnetic properties, the fill for dust has to be much higher, so it's not a trivial exercise.

I'm not sure what mix has been achieved with ferrite, to date, but you might expect something similar with other fillers. The ferrite composites are all low temperature materials that are presented as sheets.

There are some filled thermoplastics in effective service as heat-transfer materials. Perhaps that technology is closer, though I doubt it welcomes completely foreign metallic particles any better.

Of course you save the article, along with info on source. Will it still be there tomorrow? This is just the sort of content that the Wayback website doesn't archive.

'Good' is relative. How big do you want your 'stupid example' or 'microconverter follies' folder to get?

It's just a picture - you can bet that the interpretation of it's content is explained quite differently (if at all), depending on who does the 'splaining'.

There should always be bordering present in the legend for these things - a colour that you can point to on the scale and say 'Well at least nothing there got this hot.' It's a guarantee that the hottest point isn't hotter than presented, and that the ambient is really ambient.

RL

Not mine. It's actually nanocrystaline, but googling either gets you there.

RL