Parasitic Inductance Cancellation for EMI Filter Capacitors Using Mutual Coupling

Parasitic inductance of capacitors degrades the high frequency (HF) performance of electromagnetic interference (EMI) filters. In this paper, a new method of equivalent series inductance (ESL) cancellation for capacitors is proposed systematically. Firstly, a two-port network using mutual inductance is modeled and analyzed for parasitic inductance cancellation, and formulas deduction is demonstrated. Then, a symmetrical PCB layout is proposed for implementation. Finally, the proposed method is verified by experimental results. In the studied case, the ESL of the X-capacitor has been effectively cancelled up to 40MHz. And the differential-mode (DM) noise of the active clamping flyback converter can be reduced obviously from around 3.5MHz to 30MHz.