Parasitic Inductance

Parasitic inductance in switch loops, DC bus, and rectifier connections stores energy that rings at turn-off. It scales with loop area and path length — the enemy of clean waveforms in compact receiver boards and floor pad modules.

A schematic with ideal wires hides nanohenries that push VDS beyond rating.

01Sources

• Long traces between cap and FET, or FET and coil terminal.
• Connector pins and wire bonds in package.
• Asymmetric return path forcing current around large loops.

02Mitigation

Co-locate components; use plane returns; parallel vias; optional snubber only after minimizing L. Measure loop inductance with impedance analyzer or step response.

03WPT impact

• Ringing detunes effective tank behavior sensed by control.
• EMI peaks at ring frequency — filter may not help if source L is large.