Reduction and Cancellation Techniques for the Near Field Capacitive Coupling and Parasitic Capacitance of Inductors

In this paper, a near field capacitive coupling problem due to PCB layout is first identified. Methods to extract the capacitances in a multi-conductor system are introduced to help analyze the problem. A practical case of common mode choke design in ac/dc adapters is introduced and analyzed. Principles are given to avoid unnecessary coupling and reduce the parasitic coupling capacitance as much as possible in PCB layout design. A technique is proposed to fully cancel the parasitic coupling capacitance as well as equivalent parallel capacitance of the common mode choke. Simulation and experiment results verified the technique.