Core losses in dual big inductors

What? Won't that Larkin "Skeptic" work for you? It has >100% efficiency >:-} ...Jim Thompson

looks like coilcraft msd1583 is a bit bigger and only 0.6mm taller

try put in some numbers:

-Lasse

Thanks, got to order some of those tomorrow. If we can get them into the layout.

Those simple calcs aren't useful. For example, they do not take voltage swing across windings into account and that is a major factor in core loss. I just got 130C temperature rise :-)

Nickel/Zinc ferrites have low core losses at high frequencies. You could bu y them as RM cores when I last looked, which is quite a while ago. Farnell now stocks just three toroids which I can easily identify as Ni/Zn ferrites , but more specialised suppliers may do better.

This still leaves you with getting the cores wound by that almost extinct s pecies, the low volume coil winder, but I'm sure that if you had to find on e you could manage it.

Isat is 6A, L goes down 30%.

You sure its not copper losses?

I'm a skeptic of your assumtion of core loss ;)

Cheers

For the 10uH coil it's 11.2A.

Yes, that is also what the Bourns engineer said when I told him the story and asked for core loss data.

Tomorrow afternoon we'll know more :-)

Might a boost or boost-doubler configuration work? Is it always stepping up?

The boost-doubler should use the copper better, because there's only one winding that has to carry the load current. Pure boost is even better because it rides directly on the input voltage; the first bunch of volts are free.

How tall can you stand? Coilcraft has some nice parts. Maybe you could parallel two (or more!) if you have area but no height.

I just got a copy of Switching Power Supply Design, 3rd Ed, by Pressman et al, mostly to check on prior art. It has a lot of weird switcher configs, including a 2-phase flyback. Which could be a 2-phase boost or boost-doubler.

Strangely, they don't mention either the sepic or the boost-doubler.

If you actually know anything about switchers or about magnetics, you've never presented any evidence here.

Have you tried higher frequency? (and possibly lower inductance at the same time) Core loss increases with frequency (f^m), but if all other is kept the same, the flux density is lowered and resulting losses are reduced (B^n). n is normally higher than m

You could try reducing the inductance at the same time to reduce RDC losses

Cheers

Klaus

Download the Epcos tool and try different operating points:

Cheers

Klaus

How come your latest version uses the very same off-time control I posted in...

Subject: Re: Larkin_Skeptic_NoLimit - LTspice_Larkin_Skeptic_NoLimit.png Date: Mon, 15 Jul 2013 13:00:01 -0700 Message-ID:

Exactly what I did in __1974__...

Modernized and posted here...

I've presented plenty of evidence here of my exceptional talents ;-)

Actually, my 1974 version does something else that provides a nice stabilizing feature... something that Larkin missed... Klaus found the instability in Larkin's "design". Can anyone find it in that old pencil drawing?

I left it out of the version above because I couldn't see anyway to do it, except at the transistor level... and I didn't want to get Larkin all confused and screaming again >:-} ...Jim Thompson

Probably because I've been posting similar things for years now.

Almost 40 years ago! But not exactly.

Did you invent the peak-current-sensing boost/flyback converter? Did you patent it?

You will observe, if you're competent (and that's not proven), my __1974__ circuit indeed switches off on a maximum current, has controlled off-time based on two inputs: output voltage and... (let's see if you're observant :-) ...Jim Thompson

Yes, we've tried higher frequency. Then the inductor almost began unsoldering itself. On the FLIR image it looked like a nuclar meltdown. But we did order one inductor with less inductance, just in case, to try running the thing faster.

Thanks, I'll try that. Except I don't know what ferrite the various mfgs use and they won't tell me.

Unfortunately not. It has to work with several input voltages and the output must be controllable from 0V to 80V.

Yeah, I could really use the "first bunch of volts for free" here, because bunch would mean 20-30V. But, can't have it.

About 0.400" would be the limit. Area is really tough, the board looks like a subway in Tokyo during rush hour. Lasse suggested a bigger one but if I tell my layouter he is probably going to faint.

I was really disappointed that this core didn't perform better.

That's one reason I don't buy books much anymore. The real tricky stuff often isn't in there.

Of course I saw that. But did you invent the peak-current flyback architecture?

Of course not, but neither did you. I do think my hold-off-time method is unique. Have you deduced how the other hold-off-time input works yet? ...Jim Thompson

I tried the boost-doubler, and it works step-up or step-down. As Rob says, it's a Sepic without the second winding.

Core loss is a wash, but copper is 2:1 better.

Copper is really not problem at all, we could easily live with 200mOhms here. It's the core loss that literally cooks them.

One problem with ferrite is that it generally doesn't lend itself to be heatsinked.