Flyback transformers, small, high power, where?

Kool-mu toroid? Kool-mu seems to be about as good as permalloy powder, at a fraction of the price.

A full PFC supply at 15 watts seems like a lot of overhead per watt to me.

I'm buying a 65 watt MeanWell PFC supply for $16 in small quantities!

Wurth did some nice custom transformers for us.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

Have your board guy lay out a planar transformer. Disclaimer: you didn't specify board area per se, only height. Though you'll still have a hard time with overall dimensions coming in under a parallelepiped of the specified dimensions...

Don't think I've heard of Kool-Mu in planar E's.... would be cool though...

Tim

-- Deep Friar: a very philosophical monk. Website:

Believe it or not, this time cost is not the main concern. Size is though. If the core loss amounts to a watt or so that'll be ok.

We have to do it because PF rules start to apply when you offer installations where there's dozens of these in one location. Because of the small space we must PFC via flyback first to get to a non-isolated LV section as fast as possible. That LV are would contain post converters and won't need so much in creepage distances. It'll be a small and most of all very skinny product.

Good idea, although AFAIK Wuerth only does ferrites.

--
Regards, Joerg

http://www.analogconsultants.com/

Can't do that because the other side is already full of parts and must be low voltage. It wouldn't help anyhow because there's hardly any head room. Plus we must remain around 100kHz.

--
Regards, Joerg

http://www.analogconsultants.com/

Do you even have enough volume available to get where you want at

100kHz? There's only so much energy that you can store in a cubic millimeter of core (or air gap), and that energy times your switching frequency is your power. If you want to violate that constraint you don't need to come to us, you need to explain to God how he got the laws of physics wrong.

You quote height and width -- does that mean it can be a foot long? Why can't you take four or five of your 5W gapped ferrite transformers and string them in parallel?

I don't have anything directly to help you, other than the observation that you may be up against fundamental physics, and therefore you may need to apply some of your cleverness in the direction of getting your frequency up, rather than trying to stuff an impossible energy density into whatever materials are available here in the real world.

(I'd be looking at a microprocessor with PWM and ADC, but that's me, and it doesn't necessarily mean that I'd come out the other side of the exercise smelling like a rose, either. ADC -> software -> PWM -> gate driver = joy. Or maybe lots of smoke).

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

They also sell inductors and transformers. I bet John bought quite a bunch of custom transformers. Last time I asked Wurth they had an MOQ of 20k pieces.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

They also think they're wurth a lot!

Not for the usual ferrite that pegs at about 0.5T. Other more modern stuff can do 1.5T or even better. Most of that is distributed gap.

As a kid I've redlined an iron powder core in a balun because I didn't have enough money to stack two of them ... *PHOOMP* ... thwack ... and the antenna lay on the ground. Now I was down to zero cores :-(

But back then dash-2 from Amidon was the best money could buy for use at several MHz. It's been over 30 years.

Not that way, because then you have to keep them at a distance to fulfill creepage path regs. The core could be longer, within reason. Like an inch or maybe more. But unfortunately only lengthwise, the contacts can't be on the sides for discharge clearance reasons.

The reason I am asking here is that there are materials with a saturation flux density several times higher than ye olde ferrite. So I'd like to see if a smaller flyback xfmr can be build with any of those. From what I understand the core losses would be somewhat higher. If that's not a whole lot of added loss it may be an option.

uCs are very poor switch mode controllers. Every time that was done (usually against my advice) they couldn't get the loop bandwidth high enough because the thing plain ran out of MIPS. I have to live with what's there in terms of ICs.

--
Regards, Joerg

http://www.analogconsultants.com/

That MOQ is ok (after sampling), but their flyback stuff is huge, all regular ferrite.

--
Regards, Joerg

http://www.analogconsultants.com/

I'm not sure what's your "lengthwise". Could you stack E-cores? Clearly you won't get a bobbin if you do that, but if the $$ is there it may work.

Well, there is that. Hey! Get Jim to make you a custom chip!

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

No, they did audio-like laminated transformers for us. I think they will do anything that has inductance.

I've emailed you the contact info for the local rep.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

We bought 1K small custom transformers, but they quoted smaller quantities.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

We may have to stack. Ugly but ... man's gotta do what man's gotta do. Problem will be to cajole a xfmr mfg into doing that. They are usually very reluctant when it comes to unorthodox stuff.

BTW, table 3 in here is why I think there may be a change to shatter the old size rules:

There's also EMC. If you get above 150kHz all hell breaks loose in terms of conducted EMI. The filters will easily eat up all save real estate.

--
Regards, Joerg

http://www.analogconsultants.com/

If they are open to Kool Mu and stuff, maybe they can pull it off.

Thanks, I'll call her tomorrow. IIRC my client has a good relationship with them but we hadn't looked at them yet because there were no other cores on their site.

--
Regards, Joerg

http://www.analogconsultants.com/

The creepage doesn't change until you've successfully isolated the source - it's all hazardous until you provide a reinforced isolation barrier.

If you're doing this in two stages of basic isolation, then the line-input PFC section will need to be basic-isolated from the 24V output, as a first stage.

Telecom stuff does this - basic isolation to battery bus, then basic isolation to user ground-referenced outputs.

RL

This is unfortunate, because using the printed wiring is the most commonly used method of jumping the low profile power barrier and reducing or distributing surface temperature rise.

Your LT3798 app gives a table of parts illustrating what happens using conventional shapes. None claim a power handling density greater than

3w/cm^3. You're asking for 15W/cm^3.

RL

In my experience I always had to do (most of) the transformer design myself when I needed a custom transformer.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

It isn't a popular method because that way you cannot reasonably get the number of turns for a 180V peak primary. The only time I have seen planar transformers is in signal isolation or pulse transformers.

In the core, yes.

--
Regards, Joerg

http://www.analogconsultants.com/

Sure, that's why we want to do the flyback-PFC. Because that puts the iso barrier as far forward as possible. The bulk caps are then on the non-mains side which is a huge advantage versus boost-PFC when real estate is of the essence.

This is a hi-rel app so we have to be extra careful. Longer creepage paths and so on. So we want to minimize the primary side circuitry. Ideally without having to go above 150kHz.

--
Regards, Joerg

http://www.analogconsultants.com/