Active clamp flyback patents typically claim a clamp switch and capacitor across the transformer's primary that recycles leakage-inductance energy and enables zero voltage switching on the main switch, usually in single-switch, isolated designs. LLC resonant converter patents instead claim a resonant tank of inductance and capacitance driven by a half- or full-bridge switch pair, tuned to achieve zero voltage switching across a wider load range. Both families intersect heavily in this dataset because they share control problems — synchronous rectification timing, light-load efficiency, and magnetizing current management — even though the power stages differ. A given patent may claim elements of both if it describes a hybrid or adaptive topology.

The ranked assignee list in this dataset covers 100 companies, with the leading filer holding 25 of the 372 records in scope and the fifth-ranked filer holding 12. The top 5 assignees combined account for 22.6% of all records, and the top 10 account for 33.3%, meaning most of the field sits with companies outside that leading group. This is a moderately concentrated field rather than one dominated by two or three players, so a freedom-to-operate review needs to look well past the top few names.

Filing activity peaked at 40 records in 2018, eased over the following years, and then grew again: 2021's 29 records rose to 33 by 2024, a +14% increase over that three-year span. Figures for 2025 and 2026 in this dataset appear lower, but publication typically lags actual filing by roughly 18 months, so those recent years are undercounted rather than genuinely quieter. The most defensible read is that filing activity has been rebuilding since a mid-decade dip, not shrinking.

US7193866B1 claims a half-bridge LLC resonant converter architecture in which the controller drives synchronous rectifiers on the secondary side directly, and a coupled second transformer in turn drives the primary-side switches directly, replacing conventional diode rectification with a low-conducting-resistance synchronous pair. Anyone designing a synchronous-rectification scheme for a half-bridge LLC topology should check whether their control and drive path overlaps with this transformer-coupled driving arrangement specifically. It was published in 2007, well before most of the records in this dataset, so it functions as baseline prior art that many later filings had to design around rather than a currently live enforcement risk on its own.

The IPC composition shows 96.2% of records sitting in H02M power conversion, while adjacent classes like G05F control-variable circuits (1.3%) and G01R electric and magnetic measurement (1.6%) are touched by only a handful of records. That imbalance points to under-claimed ground in control-loop implementations for light-load and burst-mode operation, and in in-situ measurement techniques for leakage inductance or magnetizing current, rather than in the core power-stage topology itself, which is comparatively dense with prior art.