EMI Filter Design – From Fundamentals to Real Designs

Explore noise types and measurement methods, distinguishing common mode from differential mode noise, and learn conducted EMI measurement on a bench with AC and DC detectors—peak, quasi-peak, and average readings.

Explore differential mode and common mode conducted noise, DM between conductors and CM to ground via parasitic capacitance, driven by dv/dt; DM dominates below 1 MHz, CM rises with frequency.

Explore how to measure EMI with a LISN, spectrum analyzer, and attenuator, including common mode and differential mode separation, impedance emulation, and Cispr standards for different test scenarios.

Explore how to measure common mode and differential mode emi in the lab using peak, quasi peak, and average detectors, with practical separation methods and measurement tips.

Investigate the meaning of insertion loss curves for off-the-shelf filters and assess if they truly meet their claims, with practical instrumentation and measurement techniques provided in the appendix.

Explore common mode and differential mode noise modeling in EMI filter design, learn how filters work and their order, and build equivalent models for differential and common mode currents.

Explore how EMI filters attenuate high-frequency noise using capacitors and inductors, and how insertion loss, filter order, and LC and CLC topologies determine placement in power and data paths.

Explore common mode versus differential mode noise, and how common mode chokes, whitecaps, and X caps shape each path, with leakage inductance enabling differential attenuation.

Examine differential mode noise with a 100 ohm line-to-line load (two 50 ohm paths to ground) and common mode noise via parasitic capacitance to ground with a 25 ohm equivalent.

Derives a common mode noise model for a half-bridge, showing 50 ohm paths in parallel become 25 ohms; uses dv/dt across parasitic CP to quantify noise and design a filter.

Understand the capacitor equivalent circuit with ESR and ESL, derive the resonance frequency SRF, and see how capacitance and type (mlcc, film) influence impedance and noise damping in buck converters.

Explore the inductor equivalent circuit, including inductance, dcr resistance, and parasitic capacitance, and how self-resonance makes inductors behave like capacitors at high frequencies, with dc bias reducing inductance.

Explore component selection and parameters for emi filter design, covering X/Y safety capacitors, film and ceramic caps, inductors, common mode chokes, ferrite beads, DC bias, SRF, and impedance.

Analyze differential mode topologies and their order slopes, and learn to select a topology based on source and load impedance for noise, including when to use a common mode branch.

Analyze single component EMI filters, comparing C and L designs, and apply C filters for high impedance sources and loads, common mode, while L filters suit stiff voltage sources.

Study multicomponent filters—LC, CL, and pi/CLC—achieving up to 60 dB per decade, with damping and topology choices for buck converters and vehicle power systems.

Identify system operating requirements, including input/output voltages and load types, and determine EMI standards and constraints; plan attenuation and topology (differential and common mode) starting with an LC filter.

Design emi filters by applying equations for pi, lc, l, and c configurations to achieve break frequencies and attenuation. Explore how source impedance shapes corner frequencies and performance with simulations.

Explore appendix four filter design equations for c1 not equal to c2, derive cp and cs, and solve for c1 and c2 from fc1, fc2, r, and l.

Explore damping and stability in emi filter design, learn to damp inductor-capacitor filters to reduce emi noise, and apply Middlebrook's theorem to lc, pi, and t topologies.

Design damping circuits for LC/CL filters using RC across shunt C or RL across series L; size RD and CD to suppress peaking from 35 dB to ~4 dB.

Analyze LC/CL filter stability in dc–dc converters using Middlebrook's theorem within the control loop. Design damping and choose Lf, Cf, Cd to keep impedance below input and verify with plots.

Explore damping and stability of pi filters, derive C1 and C2 from output impedance constraints, and design damping to suppress the second corner peak for higher attenuation.

Design damping and ensure stability for a two-stage lc filter by separating stage cutoffs, managing peaks with damping circuits, and comparing single versus two-stage ac input filters.

Learn general guidelines for designing ac input filters and evaluate an input filter for a noisy converter, choosing lc filter option, simulating with Symmetrix or LTspice, and validating against standards.

Design a differential-mode LC filter to meet EMI emission limits for an automotive OBC, using the given noise model and IEC 61851-21-1 and CISPR 25 guidance.

Model Kalman mode noise and assess the need for a Kalman filter in a differential and common-mode EMI design. Design LC filters to attenuate noise at 300 kHz.

Explore when a two-stage LC filter outperforms a single stage by comparing attenuation and inductance, using formulas and an example at 50–150 kHz, with a practical design Excel sheet.

Explore pi filter design in EMI applications by comparing single-stage and two-stage LC filters, analyzing attenuation, ESR effects, and simulation-driven optimization for a given capacitance.

Design an output filter for a converter to meet emi standards for dc and ac outputs. Explore real capacitor models, impedance behavior, and v-curves across frequency.

Part 2 demonstrates a c-filter design to attenuate 1 MHz and 6 MHz ripple on a 24 V, 100 mΩ load using film capacitors and parallelization to meet current and ESR needs.

Place differential mode filters next to the noise source and common mode filters at the module entry to localize noise and protect the rest of the circuit.