Introduction to EMC Design

Electromagnetic compatibility (EMC) is essential for reliable operation of power systems. This guide covers EMC design practices for Recom DC-DC converters.

Understanding EMC Requirements

Emissions vs Immunity

EMC involves two aspects:
  • Emissions: Minimizing electromagnetic interference generated by your system
  • Immunity: Ensuring your system operates correctly in the presence of external interference

Standards Overview

common EMC standards for power supplies:
  • EN 55032/CISPR 32: Multimedia equipment emissions
  • EN 55011/CISPR 11: Industrial equipment emissions
  • IEC 61000-4-x: Immunity standards

Input Filtering

Conducted Emissions

input filtering reduces conducted emissions on power lines:
  • Differential Mode Filtering:
    • Use X-capacitors across input lines
    • Add differential mode inductors
    • Typical values: 0.1-1μF X-cap, 1-10mH inductor
  • Common Mode Filtering:
    • Use Y-capacitors to ground
    • Add common mode chokes
    • Typical values: 1000-4700pF Y-cap, 1-10mH CM choke

    Filter Design Guidelines

    • Place filter close to converter input
    • Minimize trace lengths between filter and converter
    • Use shielded inductors for high-frequency attenuation
    • Consider resonant frequencies of filter components

    Output Filtering

    Output Ripple Reduction

    reduce output ripple and noise:
  • Output Capacitors:
    • Use ceramic capacitors for high-frequency noise
    • Add electrolytic capacitors for low-frequency ripple
    • Place capacitors close to load
  • Post-Filtering:
    • Add LC filter for sensitive loads
    • Use ferrite beads for high-frequency attenuation
    • Consider active filtering for precision applications

    PCB Layout for EMC

    Grounding Strategy

  • Minimize Ground Loops:
    • Use star grounding for sensitive circuits
    • Separate power and signal grounds
    • Connect grounds at single point
  • Ground Plane Usage:
    • Use continuous ground plane when possible
    • Avoid slots or cuts in ground plane
    • Provide multiple vias for ground connections

    Trace Routing

  • High-Frequency Loops:
    • Minimize loop area of high-frequency currents
    • Keep input and output traces close together
    • Use twisted pairs for external connections
  • Sensitive Signals:
    • Route sensitive signals away from power traces
    • Use guard rings for high-impedance circuits
    • Implement proper shielding when needed

    Shielding and Enclosure

    When to Use Shielding

    Consider shielding when:

    • Emissions exceed limits without shielding
    • System operates in high-RF environment
    • Sensitive analog circuits need protection
    • Regulatory requirements mandate shielding

    Shielding Best Practices

  • Enclosure Design:
    • Use conductive materials (metal, conductive plastic)
    • Ensure continuous contact at seams
    • Provide adequate ventilation openings
  • Cable Shielding:
    • Use shielded cables for I/O connections
    • Properly terminate cable shields
    • Minimize unshielded cable lengths

    Troubleshooting EMC Issues

    Common Problems and Solutions

  • High Conducted Emissions:
    • Increase input filter attenuation
    • Check filter component values
    • Verify filter grounding
  • High Radiated Emissions:
    • Improve PCB layout
    • Add shielding
    • Reduce loop areas
  • Immunity Failures:
    • Add transient protection
    • Improve grounding
    • Increase filtering

    Measurement Techniques

  • Near-Field Probing:
    • Use near-field probes to locate emission sources
    • Identify high-frequency current paths
    • Evaluate shielding effectiveness
  • Current Probing:
    • Measure common mode and differential mode currents
    • Verify filter performance
    • Identify coupling paths

    Design Checklist

    before EMC testing:

    • [ ] Input filter designed and implemented
    • [ ] Output filtering adequate for load requirements
    • [ ] PCB layout follows EMC best practices
    • [ ] Grounding strategy properly implemented
    • [ ] Shielding designed if required
    • [ ] Cables properly shielded and routed
    • [ ] Pre-compliance testing completed

    Conclusion

    good EMC design requires attention to filtering, layout, and shielding. Recom converters are designed with EMC considerations, but system-level design is critical for meeting regulatory requirements. Contact our FAE team for assistance with challenging EMC designs.