The dataset shows filings peaking at 32 in 2020, holding near 26 by the 2022 midpoint, and falling to 7 by the partial 2026 year. This pattern is consistent with a technology area where the core circuit-level cooling mechanisms, such as secondary-side synchronous rectification timing, had already been claimed by established players earlier in the decade. It does not mean the underlying engineering problem is solved; publication lag of roughly 18 months means the last one to two years of data will always look thinner than they eventually turn out to be, but the multi-year decline from the 2020 peak predates that lag window and is a real trend.

H02M, the power conversion subclass, holds 216 of the 340 records in this dataset and should be the anchor search class. But H02J, B60L, H05B, H01F and H05K together account for the remaining third of filings, meaning a search restricted to H02M alone will systematically undercount relevant art, particularly claims filed as part of EV onboard chargers or resistive heating circuit designs that happen to include a resonant DC-DC stage.

The corpus includes assignees ranging from established power semiconductor and philips-affiliated entities to university-linked filers, connected through a modest ten co-assignee pairings. Notably, every assignee tracked for recent-year momentum recorded zero filings in the latest year, including one with a documented -100% year-on-year change. This suggests the field's most active filing period has passed rather than being currently led by any single dominant assignee.

US8134851B2, assigned to Infineon Technologies Americas Corp. and granted in 2012, claims a resonant converter architecture where secondary-side synchronous rectification switches are timed relative to a resonant tank formed by the transformer's primary coil, an inductor and a capacitor. It blocks designs that use that specific timing relationship for secondary-side rectification control, but it does not cover every approach to secondary-side thermal management; primary-side cooling schemes, alternative rectifier topologies, and packaging-level heat spreading fall outside its claim scope. Anyone designing a new resonant converter cooling scheme should map their rectification control approach against this claim specifically rather than assuming it covers the whole field.

The classification data points to under-claimed intersections rather than an empty field: planar transformer heat spreading, GaN/SiC resonant tank thermal derating, and PCB-embedded heat paths for LLC stages all show filing activity in their broader IPC classes without a comparable concentration of thermal-management-specific claims in this corpus. EV onboard-charger resonant stage cooling is another area where B60L filings exist but dedicated thermal claims are comparatively sparse. These are starting points for a claims-level search, not guaranteed open space, and should be verified against the full corpus before drafting.