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Selection of Power Filters f or Switched Mode Power Supplies

Comprehensive guide on power filter selection for SMPS, including IL calculations, EMI measurements, and filter effectiveness analysis for CM and DM noise. Helpful conclusions and practical test setups provided.

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Selection of Power Filters f or Switched Mode Power Supplies

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  1. Selection of Power Filtersfor Switched Mode Power Supplies Konstantin Kostov Jukka-Pekka Sjöroos J. Kyyrä and T. Suntio Power Electronics Laboratory Helsinki University of Technology

  2. Content • Insertion Loss • EMI measurements • EMI measured at the line & neutral • CM and DM noise measurements • Comparison between different IL data • Conclusions Selection of Power Filters for Switched Mode Power Supplies

  3. Insertion Loss (IL) Calculations • IL measuring set up • IL data from power filter manufacturers: • Usually 50 Ω / 50 Ω source and load impedance • Also based on CISPR 17 the so-called ”approximate worst case” IL measurements: • 0.1 Ω / 100 Ω • 100 Ω / 0.1 Ω Selection of Power Filters for Switched Mode Power Supplies

  4. EMI Filter CM & DM equivalent circuits • CY = 4.7 nF • LCM = 4.2 mH • CX1 = CX2 = 100 nF • Lleak = 37 H Selection of Power Filters for Switched Mode Power Supplies

  5. Measured and Calculated CM IL Selection of Power Filters for Switched Mode Power Supplies

  6. Measured and Calculated DM IL Selection of Power Filters for Switched Mode Power Supplies

  7. Conducted Emissions Measurements Selection of Power Filters for Switched Mode Power Supplies

  8. Buck Converter Used in Measurements • fs = 250 kHz • Uin = 35 V • CE = 220 F • Uo = 12 V • L = 190 H • Io = 1 A • C = 100 F • Iin = 0.38 A Selection of Power Filters for Switched Mode Power Supplies

  9. EMI from a Buck Converter (Line) Selection of Power Filters for Switched Mode Power Supplies

  10. EMI from a Buck Converter (Neutral) Selection of Power Filters for Switched Mode Power Supplies

  11. Measuring CM EMI Selection of Power Filters for Switched Mode Power Supplies

  12. Measured CM EMI CM and DM Selection of Power Filters for Switched Mode Power Supplies

  13. Measuring DM EMI Selection of Power Filters for Switched Mode Power Supplies

  14. Measured DM EMI CM and DM Selection of Power Filters for Switched Mode Power Supplies

  15. CM Noise AttenuationMeasured, Calculated and Actual Selection of Power Filters for Switched Mode Power Supplies

  16. DM Noise AttenuationMeasured, Calculated and Actual Selection of Power Filters for Switched Mode Power Supplies

  17. Conclusions • The attenuation of a passive EMI filter operating with a SMPS can be about: • The CM IL data for 0.1  / 100  source / load impedance. • The DM IL data for 100  / 0.1  source / load impedance. • The actual IL can be a lot lower than the standard 50  / 50  IL data. Selection of Power Filters for Switched Mode Power Supplies

  18. Measured CM and DM EMI(with Tektronix A6312 Current Probe) Selection of Power Filters for Switched Mode Power Supplies

  19. DM Noise Attenuation Y3 Z2 Y1 Selection of Power Filters for Switched Mode Power Supplies

  20. CM Noise Attenuation Z2 Y1 Selection of Power Filters for Switched Mode Power Supplies

  21. Components’ Impedances Selection of Power Filters for Switched Mode Power Supplies

  22. Usually π-filters are used EMI Filter Topologyand Equivalent Circuits • DM equivalent circuit • CM equivalent circuit Selection of Power Filters for Switched Mode Power Supplies

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