EMI Filter Design, 3rd Edition

8Filter Components—the Capacitor

The differential-mode components must be of the high-Q type. The individual component Q must be high, while the circuit Q must be lowered to the point where the filter circuit is able to provide effective damping of these parasitic oscillations. Additional circuits are often added to lower the Q below 2. Throughout this book, the term sometimes used for this is dQ, which uses either the RC shunt or a series LR network in parallel with the filter inductor. The term dQ is pronounced “de Queing.” Most EMI houses buy their capacitors from qualified suppliers to ensure robustness, effective SRF, and reliability. EMI filters demand specific types of capacitors for different levels of implementation.

8.1 Capacitor ...