DC-DC converter or application for microtransformer with galvanic isolation

[miguelrdz]

Hi guys! I'm working in my thesis and I need to demonstrate the application for an (galvanic) insulated air core microtransformer with high coupling factor (k). My first thought was to build a digital isolator but I don't really see the advantage of the high coupling compared to the usual devices which use medium k transformer. Some people pointed out that DC-DC converter could be a good idea but I'm not very familiarized with them.

I did some research and I see that forward converter or flyback are the best options for the design (right?)

Which one would you consider? Can you think in any other approach?

The limitation that I see is that I'm working with an air-core transformer which is probably not ideal. Also since it is a microtransformer, the whole circuit should be as small as possible to take advange of the size feature (not CMOS design though)

Thanks in advance!

[David Hess]

Forget using a forward or flyback converter and instead use an inverter.  An air core transformer will have a very low inductance compared to its high self resonate frequency and no energy storage so think of it more as an RF transformer and drive it with the lowest feasible RF frequency as part of an inverter.

[miguelrdz]

Thank you! As you can see I’m pretty lost in that regard. I’ll do some research in RF transformers, if you know any helpful source/book please let me know.

Thanks again

[David Hess]

Probably the thing to do or at least what I would try is to add a resonating capacitor to the primary side and drive it like a resonate circuit.  This is how most of the various wireless (inductive) charging standards work.  The advantage of resonance is that the impedance seen by the amplifier is much higher and easier to deal with.

Inverters which use transformers that have a core do not usually bother doing this because the high inductance of the transformer makes it unnecessary.  One exception however is the resonant Royer inverter which is often used to drive fluorescent lamps.