《全套电磁兼容资料10.》.pdf

Parasitic Components Outline • Conductor parasitic elements – resistance – inductance – capacitance • Resistors • Capacitors • Inductors • Ferrite beads • Parasitic components in circuit layout • Transformers 1 Relevant EMI “Components” • Only one third of the components affecting EMI are on the schematics • Another third are parasitic elements within components • The final third are created by PC board trace routing, and component mounting, placement, and even orientation • Any peace of wire and PCB trace has a nonzero impedance 2 Resistance of a Cylindrical Conductor Uniform current distribution inside the conductor D W 4 DC: rDC = 2 [Ω / m] σπDW (σ = conductivity) 3 Resistance of a Cylindrical Conductor δ Non uniform current distribution inside the D conductor due to skin effect W 1 AC: δ = Skin depth (σ = conductivity) µ σπf 0 1 µ0 r ≅ f [Ω/ m] AC DW πσ 4 Resistance of a Rectangular Conductor Average depth of current penetration T δ W AC resistance: