title: COSEL Power Supply, Noise Filter 2025 Product Catalog

Summary

COSEL Power Supply, Noise Filter 2025 Product Catalog

4Noise Reduction3 Combining Multiple EMI FiltersIf one EMI filter cannot provide sufficient attenuation, the attenuationeffect can be improved by connecting two filters in series.However, one must pay attention to the fact that it will result incombining the leakage current and voltage drop of two EMI filters.ConnectionEMIFilterConnection4LINE LOADTAC-30EMIFilterLINE LOADTAC-30ConnectionEMIFilterLOAD LINEConnectionTAC-30EMIFilterLINE LOADTAC-30EMIFilterLINE LOADTAC-30EMIFilterLOAD LINETAC-30EMIFilterLOAD LINETAC-30External Ferrite CoreMotordriverMotordriverMotordriverMotordriverFigure 4.3.1 Example of EMI Filter Connection DirectionsWhen connecting two EMI filters, the direction in which they areconnected may also cause difference in the attenuation characteristic.Figure 4.3.3 shows the results of comparing the attenuationcharacteristics (static characteristics) due to different directions inwhich two EMI filters are connected.Figure 4.3.4 shows the actual sample noise characteristics caused bythe connection directions.Unlike the static characteristic data, connection does not improvethe attenuation in this case. This phenomenon occurred because theinput and output impedances of the EMI filters were different from theconditions of static characteristics.When trying to optimize the way EMI filters are connected, one mustevaluate by checking actual noise levels.If one EMI filter cannot provide sufficient attenuation, the effect canbe improved by inserting an external core.Whether a core is inserted on the LINE side or on the LOAD side ofan EMI filter may cause difference in the attenuation characteristic.CoreEMIFilterLINE LOADTAC-30CoreMotordriverMotorMMotorMMotorMMotorMMotorMFigure 4.4.1 Example of Placing an External CoreWhen adding a core on the LINE side, one needs a core that cangenerate sufficiently large inductance for the choke coil within the EMIfilter.Just inserting on the LINE side a core whose performance is equal toor less than that of the internal choke coil does not contribute toreducing noise.When inserting it on the LOAD side, it will produce a large attenuationeffect because the circuit takes a configuration of a T-type EMI filter circuit.Level [dBμV]Attenuation [dB]Level [dBμV]Level [dBμV]10090807060 One set Connection5040302010 Two set Connection00.1 1 10 100Frequency [MHz]0102030405060708090100110? 771 ?Figure 4.3.2 Example of Effect of CombiningMultiple FiltersConnectionConnectionConnection1200.010.1110100Frequency [MHz]Figure 4.3.3 Comparing Static Characteristics ofDifferent 2-filter cofigurations10090807060Connection504030Connection2010 Connection00.1 1 10 100Frequency [MHz]Figure 4.3.4 Comparing Effects of Different2-filter Configurations1009080The LINE side core insertion70With no core6050403020The LOAD side core insertion1000.1 1 10 100Frequency [MHz]Figure 4.4.2 Example of Effect of Adding an ExternalFerrite CoreTechnical Notes-13EMI/EMCFilter