Who makes small swinging chokes?

I wasnt aware of any application for them nowadays.

NT

Switch mode converters, for example. When you must cover a wide range of outputs then ripple can become critical at very low output levels. That's where the converter chip can usually only work in pulse skipping or burst mode because it cannot otherwise get below its minimum duty cycle. This is where you'd want a really large inductance but you can't afford it for cost and size reasons. A swinging inductor would fit like a glove because it's small. The inductance largely collapses to the usual small value at high current but that's ok.

That's cool, Joerg. I wish I knew more about inductors/ magnetics. If it's a large volume can't you ask someone to make it for you? X many turns of Y daimeter wire on Z piece of material. I guess you'd have to run the numbers on the coil. API Delevan, is just up the road from where I live.

George H.

To be able to stand being a 'swinger', I expect it helps to be fully saturated at all times. :(

Cheers

Phil Hobbs

Not a commodity, because there's no concensus on what the slope should look like. You can wind toroid sets on an smd platform (40705TC +

What are you using, so far, to prove that this is a cure to all of your light-load problems? (See what I mean?)

RL

How about paralleling two stock SMD inductors with different saturation points?

(Joerg might wince at two parts and double real-estate, though.)

-- Cheers, James Arthur

Thanks for explaining. Funny how obsolete tech comes back into use.

NT

Um, on 2nd thought, series-connection's more reasonable, values-wise, but the series resistance might be a nuisance.

-- Cheers, James Arthur

Especially since they'd both have to be swinging chokes for it to work. ;)

Joerg's idea of stacking high- and low-mu cores and running the winding through both of them sounds like the ticket.

Cheers

Phil Hobbs

Yes, if we can't get it anywhere it'll have to be custom. But the challenge will be Z. If that requires two toroids side be side we'll receive lots of "decline to quote" replies.

"Can I have that with fries instead of mashed potatoes?" ... "No, sorry". ;-)

It's just that some engineers and even professors think it's obsolete. In power industries swinging inductors are still in wide use. You can order one today from ABB. But delivery will be on a flatbed trailer and you'll have to provide a crane :-)

Reminds me of a design review where a filter was flagged as inadequate and they didn't have room or budget for anything better. I was just an invited reviewer and then raised my hand. "Maybe we could use a Q-multiplier there" ... "A what?"

So far just calculations. I'll also simulate it but only if I can be sure that we can get those things at reasonable cost. Else it'll be a nice circuit but would remain a pie in the sky.

is

you

No, they don't have to both be swinging choke.

Here--put two in series, L1, a high-valued low-esr choke that saturates easily, and L2, low-valued and high-saturation current.

=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D .-.-.-. .-.-. _________| | | |_____| | |____ L1 L2

At low currents, the inductance is L1+L2.

Once L1 saturates, it's a resistor (low-valued, by design), and L2 takes over.

-- Cheers, James Arthur

No, in a series connection they don't have to be. But the transfer will be rather abrupt, cost roughly doubles and real estate needs are doubled. For the high-inductance one you'd have to use a CM choke so its wire can carry the current but those are large and usually saturate whambam style.

But it'll be custom and can't be done with the usual SMT-friendly cores :-(

My dream would be if someone cooked up the needed material so it's one core with a loooong saturation slope (meaning not totally flattened out but almost).

;)

The saturation doesn't have to be all that abrupt--IME saturation comes pretty gradually.

I've used some inductors as swinging chokes all on their own, driving them to ~2x their saturation rating ("saturation" defined as 20% inductance reduction). The result is greatly reduced inductance at high current--a swinging choke.

Those were custom-wound, with fat wire to keep I^2*R losses reasonable. About a 3 to 5:1 swing, IIRC.

As for cost, you'll have to weigh the cost of spec'ing a custom, boutique part, against buying two mass-produced units easily available at DigiKey.

-(

You can put those in series too, if it satisfies your swing ratio. A super-wide ratio might be hard.

-- Cheers, James Arthur

Yep. I now have my Spice model refined for a smoothly converging saturating inductor, if anyone is interested. ...Jim Thompson

They both have to be swinging chokes if they're in _parallel_, because otherwise all you get is the lower-valued one until the higher-valued one saturates, at which point you get an air-core coil.

(I understand about the series connection--I was just pulling your chain.)

Right, I was just teasing James about the parallel idea.

You could run a thin saw cut most of the way through the core on one side.

Cheers

Phil Hobbs

Only if useful in LTSpice though. I have used saturable cores in LTSpice but haven't used too elaborate a function. And I'll have to dig in really old stuff to find it :-)

The main issue with two inductors in series is that the mfg for L1 won't release saturation data, at least not in writing. Because you aren't s'posed to do that. But I hafta. You can measure it on the impedance analyzer and use the found data in the design and everything is peachy. Then one sunny day Murphy strikes, the day the mfg changes ferrite vendors ...