I am currently thinking of designing a planar transformer for my SMPS application. The input voltage will be somewhere in the region of 150V, the output voltage in the region of 1.5kV.

First of all, I have noticed a severe lack of information on the internet that discussed the design process for planar transformers. Typing "Planar transformer design guide" tends to just get me companies trying to sell me their planar transformers. I wish to design my own. Does anyone know of any good material that discussed the actual design of a planar transformer - such as the selection of primary turns, secondary turns - winding configurations, etc.

Furthermore, my transformer must be insulated above 10kV for safety reasons - 1.5kV is not my final output voltage. I am looking online and have noticed that the insulation is typically achieved by placing thin sheets of insulators between the primary and secondary PCB boards stack-up. I have attached such an example for illustrative purposes.

My question is - does each layer of insulation between the primary, secondary PCB boards need to be the entire 10kV? Or does the total isolation between the top board, and the bottom board, need to be 10kV?enter image description here

To me, it only makes sense that the insulation should be 10kV/insulating layer, since there will be high voltages between each of the secondary PCB stacks.

Additionally - what materials would be recommended to insulate a transformer at such voltages? I have seen Teflon, "FR4" and the like which are used for HV insulation applications

How can we tell which insulators would be good at High frequency? It is to my understanding that insulators lose their properties at high frequency. This info doesn't tend to be held in data sheets for these insulating materials!

  • \$\begingroup\$ How far down the rabbit hole are you expecting the answer to this question to go? Do you already have the necessary background (e.g. selection of core, primary & secondary turns) to design a "conventional" (wire-wound) transformer, and you're just looking for the differences between that and planar? \$\endgroup\$ – mlp Aug 5 '19 at 20:02
  • \$\begingroup\$ This isn't a question about planar transformers it seems - the questions you ask are totally relevant to any switching transformer or indeed any transformer generally. So, to echo what @mlp says - how would you design a transformer generally to deal with this requirement? Do you have that knowledge? \$\endgroup\$ – Andy aka Aug 6 '19 at 7:17
  • \$\begingroup\$ @mlp These are both very fair points. I am a PhD student in my first year of studies, so I have a small amount of background on transformer design, but not at a level where I would be confident to say I have the necessary background to successfully design a wire-wound transformer yet. But I am still looking to discover the differences between that and planar - however find it difficult since there seems to be a lack of literature on the topic. \$\endgroup\$ – jvnlendm Aug 7 '19 at 14:35
  • \$\begingroup\$ @Andyaka see above comment. \$\endgroup\$ – jvnlendm Aug 7 '19 at 14:36

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