In this dataset, it means a filing that combines a bidirectional DC-DC converter architecture with a specific magnetics claim — an integrated transformer-inductor structure, a planar transformer, a power inductor design, or passive-component integration onto or into the converter board. The search is deliberately narrow: general converter control or switching-scheme patents that do not touch the magnetic or passive structure are excluded. That is why the corpus is only 45 families despite bidirectional DC-DC converters themselves being a large, well-populated category.

The filing trend in this dataset rises from 3 records in 2017 to a peak of 7 in 2018, then drops to zero by 2022 and stays there through the most recent tracked year. That is a genuine decline rather than a reporting artefact, since it appears well before the window where publication lag would normally suppress recent counts. It likely reflects either a maturing claim set around the dominant integrated-magnetics designs, or filers shifting emphasis toward converter control and semiconductor-side innovation instead of the magnetics component itself.

The tracked assignee set includes a mix of Japanese electronics and automotive manufacturers, Chinese universities and component makers, and a Danish technical university, alongside a US-based research-focused filer. None of these organisations shows any filings in the latest tracked year, so leadership in this niche is currently better read as historical position rather than active momentum. Co-filing is rare across the whole dataset, with only five co-assignee pairs recorded, and the strongest of those are academic researcher pairings rather than corporate partnerships.

US20200211765A1, filed by Marelli Corporation, claims a planar transformer built from offset primary and secondary planar air-core coils sandwiched by matching planar cores, with a secondary coil section that deliberately does not face the primary coil along the winding axis. That specific offset-and-non-facing geometry is the narrow feature a competing design needs to clear, not planar transformers in general. Designs that keep primary and secondary coils fully facing and centred on a shared axis, or that use a different core-stacking arrangement, sit outside the literal claim scope, though a full clearance opinion should check the dependent claims and file history too.

The clearest gaps sit in the IPC branches adjacent to the core H02M/H01F cluster: printed-circuit-integrated passives (H05K), semiconductor-embedded magnetics (H01L overlap), and EV-propulsion-specific bidirectional magnetics (B60L), each represented by only a handful of records against a 39-strong H02M core. These thin counts suggest claim space that has not been heavily tested, particularly for board-level co-design of magnetics and passives rather than standalone component claims. Any filing strategy targeting these branches should still be checked against the dominant 2004-era integrated-magnetics lineage, since that prior art has the highest citation weight in the corpus.