Forums

Flyback transformers, small, high power, where?

Started by Joerg August 2, 2012
Folks,

Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will
run in full PFC fashion with the ouput voltage sloshing around, meaning
peaks more like 20W but average power under 15W. 100kHz switcher
frequency, because of a dearth of available PFC-flyback chips at higher
and because EMC above 150kHz would be tough here. Most likely we'll use
the LT3798.

Here is the pickle: The transformer cannot be more than about 250mils
high and a little over 500mils wide. Gapped ferrite gets us to less than
5W. Soooo ... got to look at newer stuff like Kool Mu, Ni-Fe High-Flux,
Sendust. Probably will come with some core loss penalty but the main
issues is that I can't find small E-cores there.

Does anyone have an idea? Does anyone know a switcher transformer
manufacturer who'd likely be willing to tackle this transformer design?

-- 
Regards, Joerg

http://www.analogconsultants.com/
On Thu, 02 Aug 2012 14:42:14 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Folks, > >Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will >run in full PFC fashion with the ouput voltage sloshing around, meaning >peaks more like 20W but average power under 15W. 100kHz switcher >frequency, because of a dearth of available PFC-flyback chips at higher >and because EMC above 150kHz would be tough here. Most likely we'll use >the LT3798. > >Here is the pickle: The transformer cannot be more than about 250mils >high and a little over 500mils wide. Gapped ferrite gets us to less than >5W. Soooo ... got to look at newer stuff like Kool Mu, Ni-Fe High-Flux, >Sendust. Probably will come with some core loss penalty but the main >issues is that I can't find small E-cores there. > >Does anyone have an idea? Does anyone know a switcher transformer >manufacturer who'd likely be willing to tackle this transformer design?
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. http://www.we-online.com/web/en/passive_components_custom_magnetics/products_pbcm/transformers_and_custom_magnetics/power_transformers/Planar_Transformer.php -- 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: http://webpages.charter.net/dawill/tmoranwms

"Joerg" <invalid@invalid.invalid> wrote in message 
news:a80ahqF9jdU1@mid.individual.net...
> Folks, > > Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will > run in full PFC fashion with the ouput voltage sloshing around, meaning > peaks more like 20W but average power under 15W. 100kHz switcher > frequency, because of a dearth of available PFC-flyback chips at higher > and because EMC above 150kHz would be tough here. Most likely we'll use > the LT3798. > > Here is the pickle: The transformer cannot be more than about 250mils > high and a little over 500mils wide. Gapped ferrite gets us to less than > 5W. Soooo ... got to look at newer stuff like Kool Mu, Ni-Fe High-Flux, > Sendust. Probably will come with some core loss penalty but the main > issues is that I can't find small E-cores there. > > Does anyone have an idea? Does anyone know a switcher transformer > manufacturer who'd likely be willing to tackle this transformer design? > > -- > Regards, Joerg > > http://www.analogconsultants.com/
John Larkin wrote:
> On Thu, 02 Aug 2012 14:42:14 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Folks, >> >> Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will >> run in full PFC fashion with the ouput voltage sloshing around, meaning >> peaks more like 20W but average power under 15W. 100kHz switcher >> frequency, because of a dearth of available PFC-flyback chips at higher >> and because EMC above 150kHz would be tough here. Most likely we'll use >> the LT3798. >> >> Here is the pickle: The transformer cannot be more than about 250mils >> high and a little over 500mils wide. Gapped ferrite gets us to less than >> 5W. Soooo ... got to look at newer stuff like Kool Mu, Ni-Fe High-Flux, >> Sendust. Probably will come with some core loss penalty but the main >> issues is that I can't find small E-cores there. >> >> Does anyone have an idea? Does anyone know a switcher transformer >> manufacturer who'd likely be willing to tackle this transformer design? > > Kool-mu toroid? Kool-mu seems to be about as good as permalloy powder, > at a fraction of the price. >
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.
> A full PFC supply at 15 watts seems like a lot of overhead per watt to > me. >
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.
> I'm buying a 65 watt MeanWell PFC supply for $16 in small quantities! > > Wurth did some nice custom transformers for us. > > http://www.we-online.com/web/en/passive_components_custom_magnetics/products_pbcm/transformers_and_custom_magnetics/power_transformers/Planar_Transformer.php >
Good idea, although AFAIK Wuerth only does ferrites. -- Regards, Joerg http://www.analogconsultants.com/
Tim Williams wrote:
> 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... >
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/
On Thu, 02 Aug 2012 14:42:14 -0700, Joerg wrote:

> Folks, > > Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will > run in full PFC fashion with the ouput voltage sloshing around, meaning > peaks more like 20W but average power under 15W. 100kHz switcher > frequency, because of a dearth of available PFC-flyback chips at higher > and because EMC above 150kHz would be tough here. Most likely we'll use > the LT3798. > > Here is the pickle: The transformer cannot be more than about 250mils > high and a little over 500mils wide. Gapped ferrite gets us to less than > 5W. Soooo ... got to look at newer stuff like Kool Mu, Ni-Fe High-Flux, > Sendust. Probably will come with some core loss penalty but the main > issues is that I can't find small E-cores there. > > Does anyone have an idea? Does anyone know a switcher transformer > manufacturer who'd likely be willing to tackle this transformer design?
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
Joerg <invalid@invalid.invalid> wrote:

>John Larkin wrote: >> On Thu, 02 Aug 2012 14:42:14 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Folks, >>> >>> Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will >>> run in full PFC fashion with the ouput voltage sloshing around, meaning >>> peaks more like 20W but average power under 15W. 100kHz switcher >>> frequency, because of a dearth of available PFC-flyback chips at higher >>> and because EMC above 150kHz would be tough here. Most likely we'll use >>> the LT3798. >>> >> >> Kool-mu toroid? Kool-mu seems to be about as good as permalloy powder, >> at a fraction of the price. >> > >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. > > >> A full PFC supply at 15 watts seems like a lot of overhead per watt to >> me. >> > >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. > > > >> I'm buying a 65 watt MeanWell PFC supply for $16 in small quantities! >> >> Wurth did some nice custom transformers for us. >> >> http://www.we-online.com/web/en/passive_components_custom_magnetics/products_pbcm/transformers_and_custom_magnetics/power_transformers/Planar_Transformer.php >> > >Good idea, although AFAIK Wuerth only does ferrites.
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=.) --------------------------------------------------------------
On Fri, 03 Aug 2012 00:28:17 GMT, nico@puntnl.niks (Nico Coesel) wrote:

>Joerg <invalid@invalid.invalid> wrote: > >>John Larkin wrote: >>> On Thu, 02 Aug 2012 14:42:14 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> Folks, >>>> >>>> Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will >>>> run in full PFC fashion with the ouput voltage sloshing around, meaning >>>> peaks more like 20W but average power under 15W. 100kHz switcher >>>> frequency, because of a dearth of available PFC-flyback chips at higher >>>> and because EMC above 150kHz would be tough here. Most likely we'll use >>>> the LT3798. >>>> >>> >>> Kool-mu toroid? Kool-mu seems to be about as good as permalloy powder, >>> at a fraction of the price. >>> >> >>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. >> >> >>> A full PFC supply at 15 watts seems like a lot of overhead per watt to >>> me. >>> >> >>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. >> >> >> >>> I'm buying a 65 watt MeanWell PFC supply for $16 in small quantities! >>> >>> Wurth did some nice custom transformers for us. >>> >>> http://www.we-online.com/web/en/passive_components_custom_magnetics/products_pbcm/transformers_and_custom_magnetics/power_transformers/Planar_Transformer.php >>> >> >>Good idea, although AFAIK Wuerth only does ferrites. > >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.
They also think they're wurth a lot!
Tim Wescott wrote:
> On Thu, 02 Aug 2012 14:42:14 -0700, Joerg wrote: > >> Folks, >> >> Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will >> run in full PFC fashion with the ouput voltage sloshing around, meaning >> peaks more like 20W but average power under 15W. 100kHz switcher >> frequency, because of a dearth of available PFC-flyback chips at higher >> and because EMC above 150kHz would be tough here. Most likely we'll use >> the LT3798. >> >> Here is the pickle: The transformer cannot be more than about 250mils >> high and a little over 500mils wide. Gapped ferrite gets us to less than >> 5W. Soooo ... got to look at newer stuff like Kool Mu, Ni-Fe High-Flux, >> Sendust. Probably will come with some core loss penalty but the main >> issues is that I can't find small E-cores there. >> >> Does anyone have an idea? Does anyone know a switcher transformer >> manufacturer who'd likely be willing to tackle this transformer design? > > Do you even have enough volume available to get where you want at > 100kHz? ...
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.
> ... 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. >
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.
> 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? >
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.
> 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. >
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.
> (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). >
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/
Nico Coesel wrote:
> Joerg <invalid@invalid.invalid> wrote: > >> John Larkin wrote: >>> On Thu, 02 Aug 2012 14:42:14 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> Folks, >>>> >>>> Got to do a flyback design, 120VAC to 24VDC or so, at about 15-20W. Will >>>> run in full PFC fashion with the ouput voltage sloshing around, meaning >>>> peaks more like 20W but average power under 15W. 100kHz switcher >>>> frequency, because of a dearth of available PFC-flyback chips at higher >>>> and because EMC above 150kHz would be tough here. Most likely we'll use >>>> the LT3798. >>>> >>> Kool-mu toroid? Kool-mu seems to be about as good as permalloy powder, >>> at a fraction of the price. >>> >> 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. >> >> >>> A full PFC supply at 15 watts seems like a lot of overhead per watt to >>> me. >>> >> 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. >> >> >> >>> I'm buying a 65 watt MeanWell PFC supply for $16 in small quantities! >>> >>> Wurth did some nice custom transformers for us. >>> >>> http://www.we-online.com/web/en/passive_components_custom_magnetics/products_pbcm/transformers_and_custom_magnetics/power_transformers/Planar_Transformer.php >>> >> Good idea, although AFAIK Wuerth only does ferrites. > > 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. >
That MOQ is ok (after sampling), but their flyback stuff is huge, all regular ferrite. -- Regards, Joerg http://www.analogconsultants.com/