> Also while I am on the topic, what about transformer design. How can I
> assure high DC isolation between the primary and secondaries of the
> transformer. Do high voltage power supplies use a different core shape
> than the standard "E" shape?
>

In commercial design, esp. in high voltage distribution transformers, this
is usually achieved by immersing the entire transformer in transformer oil.
In smaller HV transformers, such as flyback transformers, an epoxy style
encapsulant such as isophorone diamine or polystyrene is usually used.  In
neon sign transformers (NST's), the transformer is usually potted in
bitumen.

As for the core shape, this depends on the style of HV transformer.  A
single ended transformer with a single high tension out will call for a
transformer wound on a large 'O' shaped ferrite or laminate, with the
primary wound on one leg, and the secondary on the other.  Most flyback and
large distribution transformers are wound this way.

Many HV transformers however are centre grounded.  These are wound on large
E or square shaped forms with a post through the centre (window shaped).
The centre post holds the primary winding, and the two outer posts hold the
secondary windings.  In this design, the two secondaries are usually joined
at one end and grounded to the core, to create a +/- output.  This is done
to reduce core size and weight for equivalent voltage/power output.  NST's
are done this way.

Hope this helps.

Rgs,
Ian.

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