For boost, you are feeding the primary (H1, H2) as normal and putting the secondary (X1, X2) in series between the line and load. It must be connected in-phase to add its voltage to the line.
For buck, you do the same configuration, but feed it backwards. The line feeds the series combination of primary and secondary, and the comes from the tap point.
Note that this is an autotransformer, and does not offer the isolation that a conventional transformer hookup would have.
![[Linked Image from barc.org]](http://www.barc.org/n1ist/buckboost.jpg)
[Edited to fix problem in the buck description and add schematic]
/mike
[This message has been edited by n1ist (edited 03-24-2006).]
