On remand from the Supreme Court, the Federal Circuit in Lighting Ballast Control v. Philips Electronics North America affirmed the claim construction ruling of the district court, as it relied on factual determinations that were not clearly erroneous.

The district court initially had determined that the term “voltage source means” was a means-plus-function limitation, but later reversed itself, relying on expert testimony that a skilled artisan would understand it to mean “a rectifier.” In a previous en banc decision in this case, the Federal Circuit applied the long-standing Cybor rule that claim construction is reviewed de novo. Shortly after, the Supreme Court issued Teva v. Sandoz, which changed claim construction from a purely a legal question, reviewed de novo, to one where underlying “subsidiary” factual findings on extrinsic evidence are reviewed for clear error. The Supreme Court remanded this case for consideration in light of Teva.

On remand, the Federal Circuit in a panel decision reversed itself, upholding the district court’s construction of “voltage source means.” Under the Teva standard of review, it concluded that the district court’s factual findings on the expert extrinsic evidence regarding the structure were not clearly erroneous, and affirmed that the term “voltage source means” is not a means-plus-function limitation.