toroidal coils stacked 2×2, two & two opposing, pushing into the center point.

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input 0X

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https://en.m.wikipedia.org/wiki/Toroidal_inductors_and_transformers

https://en.m.wikipedia.org/wiki/Joule_thief

https://en.m.wikipedia.org/wiki/Blocking_oscillator

https://en.m.wikipedia.org/wiki/Boost_converter