Manufacturing techniques for flyback SMPS transformers - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: July 13, 2024, 11:51:02 am
content: Hi,We are doing a 48W DCDC flyback SMPS, 24 in and out, 150kHz. PQ20/16 core set.I wound the transformer NP/NS = 10/15.The sec was in two series "halves", (one 8, and one 7 turns) which "sandwich" the primary.When I wound the prototypes, I just wound the three layers, and then soldered the two ends of each primary half together,and layed this solder Joint on top of the tape which covers the "top" coil...However, I believe it will not be realistic to expect the production winders to do it like that. It wouldbe too fiddley to do on mass production basis.Therefore, for the production spec, I will bring each of the primary "half" coilsout to a pin-pair, and do it like that.Would you agree , this is the best course of action , ie , will be cheaper to produce like that?We will than just have to connect the primary half coils on the PCB with a PCB trace._________________________--___________________________Also, as you know, with any flyback transformer, the coils should be wound such that all the "dotted" ends are at the same side of the bobbin. This will reduce common mode noise. Why dont people bother doing this?Also, to ease manufacture, all coils should be wound clockwise.Clockwise is easy to understand on a vertical bobbin'd PQ20/16 core, but which way is clockwise on eg, an EFD15 bobbin.? It depends which way you hold it.You would think there would be a "method", whereby clockwise on an EFD15 is with the way its clockwise when you hold it with bobbin axis pointing to you, and pin 1 nearest you....but many bobbins dont even have numbered pins.________________________--_____________________________Also, suppose you are doing a 24vin to 24vout flyback SMPS.Suppose that the two secondary halves sandwich the primary.Also, that the primary is wound with one single coil whichcovers 2 layers.Do you bother to put tape between the two primary layers?(after all , its only 24v). I realise you can get "nicked" coils,but the taping is an extra production measure, and its cheaperto do without it.On that note, if you do put tape between the 2 primary layers, then do you prefer to wind themas separate coils, which subsequently get connected on the PCB, or just wind one layer, put thespool on a mandrel, then add the tape, then do the next layer?Obviously doing two separate coils makes it easier (and likely cheaper) to do thetaping. (that's if you bother with the taping?)Last edited: 11 minutes ago

author: MK14
author_rank: Super Contributor
timestamp: July 13, 2024, 12:22:57 pm
content: Cross-posted here, it seems:https://www.edaboard.com/threads/production-spec-for-flyback-smps-transformer.411686/#post-1777051

author: tooki
author_rank: Super Contributor
timestamp: July 13, 2024, 02:24:44 pm
content: There is simply no way Faringdon isn’t fucking with us. There is absolutely zero chance that someone could be an experienced working engineer, specialized in power supply design, and have absolutely no clue about how to procure power supply parts. You would not only know how to go about having a transformer made, you’d already have preferred suppliers and contacts at those suppliers because you’d worked with them many times before.

author: Faringdon
author_rank: Super Contributor
timestamp: July 13, 2024, 07:27:37 pm
content: Thanks,Ayk, the winders will simply do as we tell them.Ayk, there are a number of ways of getting a working flyback smps transformer done.....some will be good with EMC , some not.....all will work fine and produce the vout from vin.........the winders wont know about which are good with EMC.If we ask them about pricing between either no-tape-between 2 layer pri, or putting tape there, they will probably be cagey about this......I would say that with a 24vin flyback, having a 2 layer primary could be done with no tape between the 2 primary layers.....but i bet aerospace wouldnt allow that...in case of nicked coils. I woudlnt have any idea of exactly how much more it would cost to put tape there....it woudl certainly be a PITA for the winders...but they are unlikley to let on how much extra it woudl cost to have it done like that.....in case someone asked for thier "no tape discount"...what i am asking , is what might be the "cheaperness" for say 10000 transformers.?This is probz the best doc on flyback smps manufac...but says nothing on eg having the dotted ends of each coil all at the same bobbin end....https://www.thierry-lequeu.fr/data/TOPSWITCH/AN17.pdfAs discussed, the winders wont know either..they wont realise that the dotted ends of each coil should be at the same end of the bobbin. They need to be told this.

author: tooki
author_rank: Super Contributor
timestamp: July 14, 2024, 12:47:20 pm
content: Uh huh. Suuure. We’re supposed to believe that a transformer manufacturer doesn’t have application engineers who understand transformers and will help you come up with the best solution. And that they’re unwilling to give you quotes.And of course you’d need to agree on a pinout. I mean… duh?If you did find a transformer manufacturer that incompetent, then the solution is to seek out a better manufacturer.

author: Faringdon
author_rank: Super Contributor
timestamp: July 14, 2024, 12:51:35 pm
content: QuoteThanks, i dont know what they're like in Switzerland, but in UK, they rely on the engineer to give the info like the "dotted ends to one side."The winders know some tech stuff though...eg, they know how to make one to a certain high voltage isolation spec, or to a certain temperature spec, etc etc.....but detailed electronics details like EMC, they wont be too hot on options for that.If you spec that you dont need tape between two primary layers (ie two layers of the same coil)...then they will just do that. If you ask how much money you save by avoiding tape like that, they wont tell you how much you save......or if you spec to put tape in.....and then ask how much money they will take off if you remove the tape requirement, -they wont give you a cost reduction.They will keep the detailed costing details away from you.....they just look to see how much money they think they can get out of you.Ive known winder co's do a shield winding in a offline flyback transformer which is connected up to the flyback switching node, and they were sent a schem showing it so...but they just did it anyway!

author: Gyro
author_rank: Super Contributor
timestamp: July 14, 2024, 12:59:23 pm
content: If your method of determining whether to put tape between layers or not is just a cost then youreallyhave a competence issue!

author: Faringdon
author_rank: Super Contributor
timestamp: July 15, 2024, 06:41:17 am
content: QuoteThanks, ayk, in some cases tape is needed, but others, it can be omitted....take most OTS inductors....you dont see tape between the layers.