The major problem I see with having split windings is that you will increas= e the winding capacitance to ground which will probably not be desirable at= the frequencies you are proposing. The shield is supposed to have a connec= tion brought out and connected to ground if you are seriously looking at mi= nimising noise coupling between primary and secondary, and having such a ca= pacitance from the drive end of the winding (the end connected to the trans= istor collector or drain) is likely to produce undesirable effects. Personally I would wind it with a single shield and then make sure that on = the primary side the winding end against the shield is connected to the sup= ply rather than the transistor. -----Original Message----- From: piclist-bounces@mit.edu On Behalf Of Manu A= braham Sent: 22 July 2019 06:27 To: Microcontroller discussion list - Public. Subject: Re: [EE] Shield winding and common mode noise Hi Bob, I do remember the transformer problem you had previously. Having a shield i= s a good idea as you say. The shield what's in my mind is one layer of mylar insulation (less than 66= um), 1oz (66um) Cu foil and another layer of mylar insulation. The whole thing adds to 0.2mm thickness. An additional 2x shield foil means= 0.4mm lost in the winding area. In the preliminary situation, the idea was to have the entire primary windi= ng in one go and then the secondary later, but got a suggestion that the co= upling would get a hit and was suggested to split the windings to sandwich = them, primary-secondary-primary-secondary. Tried this topology, it works well, but the problem of common mode noises a= rises. The noise does severely affect equipment powered from it. Thus the s= hielding thought came to my mind. Multiple shields, other than loosing precious winding area, will it affect = magnetic coupling in an adverse way ? Having a split bobbin does not work in acceptable manner, as the magnetic c= oupling is severely affected in which case. Commom mode chokes, EHT transfo= rmers possible though.In the very first case the windings had to be sandwic= hed to improve coupling .. Thanks, Manu On Mon, Jul 22, 2019 at 9:39 AM Bob Blick wrote: > > Hi Manu, > Having just dealt with a common-mode problem with an audio power amplifie= r, I heartily agree that an interwinding shield is a good idea. > > But I really don't see how you can alternate with three or four windings.= Multiple shields just don't seem like something that is going to work, par= tly because each shield adds to the overall diameter and pushes your windin= gs farther and farther from the core. > > Have you tried (I have not re-read the original thread) using a split bob= bin method, rather than sandwiching the windings? I seem to recall you did,= and it didn't work as well regarding power transfer, but it is supposed to= be good regarding common-mode. > > Best regards, Bob > > ________________________________________ > From: piclist-bounces@mit.edu on behalf of=20 > Manu Abraham > Sent: Sunday, July 21, 2019 8:43 PM > To: Microcontroller discussion list - Public. > Subject: [EE] Shield winding and common mode noise > > Hi, > > I have this working SMPS with a ferrite core transformer running at=20 > about 65kHz. It's got a flyback topology handling about 65W. > > Primary is wound closest to the core and a layer of insulation exists=20 > on top of it. > Secondary is wound on top of the Primary and a layer of insulation over i= t. > > Improving the design, in terms of common mode noise, added a copper=20 > foil shield winding in between the Primary and the secondary. > > Stable output. Things look well indeed ! > > > > Now, moving on, decided to increase power from 65W to 150W max. To=20 > improve coupling, the logical thought was to split the Primary into=20 > two and the same for the secondary. > > So, the logical construction goes on as follows: > Primary#1 is wound first and insulated > Secondary#1 is wound next and insulated > Primary#2 is wound next and insulated > Secondary#2 is wound last and insulated > > Now, placing the shield winding has become a question, where do I=20 > place the shield winding(s). To achieve a similar configuration as=20 > previously, are 3 shield windings required, each between Primary and=20 > Secondary ? > > If that's true, does adding each shield winding reducing the coupling sti= ll ? > > Is such a configuration advisable ? > If not, what would be a recommendable way to reduce the common mode=20 > noise in this case where the coils are sandwiched ? > > I would like to hear what folks think about it. > > Best Regards, > > Manu > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > View/change your membership options at=20 > http://mailman.mit.edu/mailman/listinfo/piclist > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > View/change your membership options at=20 > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclis= t --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .