Big off-the-shelf SEPIC inductors?

Digikey doesn't have anything. I think Coilcraft products have a high quality and you can find their parts in many datasheets as references, e.g. voltage regulators, so maybe you should ask them.

I've bought some time ago some digital audio transformers for AES3 from Coilcraft which works good. The price was not too high. Minimum quantity was 100 parts.

Thanks, Frank, that's good to know. Although even this series is borderline, my switcher will max it out to the limits.

I'll get a quote then.

We needed just a few dozen and ended up buying the cores and winding them in-house. Not a lot of turns on an extra-beefy core, and stock parts did (from Amidon, IIRC) did the trick.

That would also be my preference but clients usually do not like that. Maybe I use two of those Coilcraft SEPIC dual-inductors in parallel. Ugly, but off the shelf. Possibly you and I are the only guys designing big SEPICs and there ain't no market for larger coils ;-)

On a sunny day (Fri, 29 May 2009 14:20:24 -0700) it happened Joerg wrote in :

Hi Joerg did you know that in SEPIC you can use standard line (mains) filters? These consist of the 2 coupled inductors, and can be had in almost any ampere any form. I have tried this with a much smaller one, and it works perfectly. ftp://panteltje.com/pub/power_pic/power_pic_working_img_0905.jpg

The bigger ones you can find here:

Note that the build in caps usually will be no problem, as these are small, and bridged by you electrolytics.

But of course I know you never have any money, and it should be available from every local drugstore.. .So and this is the case with mains filters.

any form.

and bridged

Actually, those cores saturate much faster than you'd think. For small switchers it's ok but not if 10 amps flow. Such common mode chokes can only take high currents because two wires are used with exactly opposite currents. IOW the currents cancel almost perfectly. Not the case in a SEPIC.

On a sunny day (Fri, 29 May 2009 14:58:45 -0700) it happened Joerg wrote in :

Well, I know how a SEPIC works :-)

I use a couple Coilcraft parts (MSD1260 & SER1360) in my switchers. These are for low volume production, probably no more than 200 per year. They are very easy to deal with, even with samples. Wish all magnetics companies were this easy to deal with.

I need a bit bigger than that, looks like the MSD1278 is the end of the rope in terms of off-the-shelf sizes. So I may need two SEPIC inductors in parallel. That'll look quite unorthodox on the schematic but, oh well. Prices are very reasonable ;-)

250W, isolated sepic PFC :-)

Welcome to the club :-)

Did you use off-the-shelf magnetics or custom? If off-the-shelf I'd appreciate a hint. Une bobine francaise would not be a problem in this case ;-)

We have a local coil winder here that maybe of help, small shop. would do small quantities. probably even design it for you. Email if your interested.

Cheers

Check these guys out:

Perhaps they have something standard. AFAIK their custom service isn't that expensive. We buy all inductors from them. They are cheaper than Coilcraft, sell small quantities directly from the factory and provide excellent service.

Off the shelf custom :-) I mean, the interesting part of using a (modified) sepic there was theoretical 0 input ripple, hence reduced EMI filter which is a pain with flyback PFCs and a good reason for using a boost which can't be isolated.

That required a transformer with high and controlled leakage inductance, i.e. windings on the outer leg, but we couldn't afford custom bobbins so it was custom standard magnetics with an extra inductor...

Do you remember who made the transformer itself? 250W is more than I need but bigger is better than too small ;-)

Thanks, Martin. If I can't find good off-the-shelf magnetics I'll email.

Sorry, I probably badly worded it, but it was custom wound on standard core and bobbins.

Of course you're welcomed to have yours manufactured here, but I guess you don't want this :-)

Thanks, Nico. I had looked at their WE-Flex stuff but it's all way too small. If I need custom I could even contact them in German. But not in Bavarian ;-)