Re: PFC Question

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Original poster: Ed Phillips <evp@xxxxxxxxxxx>

">     Easy.  The transformer has very close to unity coupling factor so
> the leakage inductance is close to zero.   Do a Google search on those
> terms for a better explanation.
>
> Ed

In an ideal world yes, one would like a variac to have perfect
coupling between all turns. Due to its required geometry however it
can't. The turns are spaced out in a single layer around a toroidal
core. Closest to unity coupling is only obtained by having all
windings occupying the same space, a physical impossibility but one
you can get close to with a single bobbin'd transformer wound on an E-
I core or a potcore with interleaved windings. In the same breath
it's worth saying that even interleaving has its problems - the
better the coupling obtained between primary and secondary turns the
worse becomes the coupling of each winding to itself.

Malcolm"

   I guess your objection is based on my excessive use of 
superlatives.  Perhaps I should have said "high coupling factor" and 
"low leakage inductance".  I guess I could measure the inductance 
between the brush and the two shorted ends of one and get a better 
idea, but I've never done that.

Ed