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

Selection of Power Filters for Switched Mode Power Supplies 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 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies 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 The closed loop system may even become unstable when the design infinite-precission controller is implemented with a fixed-point digital processor due to the finite precission of the parameter representation resulting from the FWL Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

EMI Filter CY = 4.7 nF LCM = 4.2 mH CX1 = CX2 = 100 nF Lleak = 37 H 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 22 September, 2018

Measured and Calculated CM IL Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Measured and Calculated DM IL Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Conducted Emissions Measurements Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

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 22 September, 2018

EMI from a Buck Converter (Line) Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

EMI from a Buck Converter (Neutral) Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies Measuring CM EMI Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies Measured CM EMI CM and DM Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies Measuring DM EMI Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies Measured DM EMI CM and DM Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

CM Noise Attenuation Measured, Calculated and Actual Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

DM Noise Attenuation Measured, Calculated and Actual Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies 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 22 September, 2018

Measured CM and DM EMI (with Tektronix A6312 Current Probe) Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies DM Noise Attenuation Y3 Z2 Y1 Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Selection of Power Filters for Switched Mode Power Supplies CM Noise Attenuation Z2 Y1 Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

Components’ Impedances Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018

EMI Filter Topology and Equivalent Circuits Usually π-filters are used DM equivalent circuit CM equivalent circuit Selection of Power Filters for Switched Mode Power Supplies 22 September, 2018