Introduction to EMI Suppression Capacitors

EMI suppression capacitors are safety-rated capacitors used to filter electromagnetic interference in AC power applications. X capacitors filter differential mode noise, while Y capacitors filter common mode noise.

X Capacitors (Line-to-Line)

Applications

  • Across AC input lines (L-N)
  • Differential mode filtering
  • Standard values: 0.01uF to 10uF

Selection Criteria

  • Voltage rating: 275V AC for 230V systems, 305V AC for universal input
  • Capacitance: Based on required attenuation and frequency
  • Safety standard: X2 for general applications

Y Capacitors (Line-to-Ground)

Applications

  • Between line and ground
  • Common mode filtering
  • Standard values: 100pF to 4700pF

Selection Criteria

  • Voltage rating: 250V AC or 300V AC
  • Leakage current limitations (typically <0.25mA for portable, <3.5mA for stationary)
  • Safety standard: Y2 for general applications

Design Guidelines

Input Filter Design

  • Place X capacitors across L-N as close to input as possible
  • Place Y capacitors from L-GND and N-GND
  • Add common mode choke for enhanced filtering

    • Safety Considerations

    • Total Y capacitance limited by leakage current
    • X capacitors require discharge resistors
    • All safety capacitors must have proper agency approvals

    Conclusion

    proper EMI capacitor selection ensures both effective filtering and safety compliance. Contact our FAE team for filter design assistance.