Sure,
When I designed HV transformers, I found that above about 3 kV, the majority
of the problems with losses, corona, ringing and so on are caused by
inter-winding capacitance and capacitive coupling to the core.
Winding the secondary with all layers in the same direction and rectifiers
inbetween layers make almost all
the trouble go away. The voltage builds up as you get away from the core.
The interwinding capacitances can then help filtering and the voltage swings
at the end of the windings will be in the same direction, i.e. zero between
windings.
Like:
-------D|---------------> HV
| =
*~~~~~~~~~ --|
| =
-------D|------ --|
| =
*~~~~~~~~~ --|
| =
-------D|------ --|
| =
*~~~~~~~~~ --|
|
GND
To get this to work, you need long, single layer, windings; i.e. Thin Wire
and good distance to the core at the ends of the windings. So the triple
insulation does not help - it displaces Air with material with higher
capacitance, putting more stress on the remaining air gaps. You get corona.
A special former split into multiple "disc" sections will also work,
provided they are "stacked" like shown. Those are easier to wind, but the
formers and cores that match them are hard to get in quantities below 200000
;-)
Resonant converters help a lot because they have lower rise times so less
capacitive current will flow and you transformer will have loads of leakage
anyway that it would be a shame to fight against.
Finally, you probably want to keep switching frequency low, 25-30 kHz
maybe - the creepage distance is what dimensions the core so you are not
going to beat the conference circut with 1 MW/cm3 anyway.
PS:
If it really has to be cheap and you do not mind cheating, a modern Ignition
Coil for a Car can typically deliver about 40 W at 12 Kv when driven from a
single end resonant converter. Flyback works too at less efficiency.
Boss didn't like that particular solution because Customer would spot the
obvious COTS part and begin to worry about what he should really pay for the
unit - which would not be good because the price tag was about 70 times the
cost ab factory!!
