title: COSEL Power Supply, Noise Filter 2025 Product Catalog

Summary

COSEL Power Supply, Noise Filter 2025 Product Catalog

2Selection of EMI Filters10Attenuation Characteristic (Static Characteristic)Attenuation characteristic provides a rough indication ofnoise reduction effect. The graph is derived from plottingan attenuation characteristic when connecting a EMIfilter to a specified measurement circuit with frequencyon the horizontal axis and with attenuation on thevertical axis.The measurement methods are shown in Figure 2.10.1and Figure 2.10.2. The attenuation is given as the ratioof U01 to U02, where U01 is output when EMI filters arenot in the measured circuit and U02 is when an EMI filteris in the circuit, and normally expressed with the logarithmof that ratio in [dB].Attenuation = 20Log 10 (U 01 /U 02 ) [dB]U 01 :Generated voltage when a EMI filter is not inserted [V]U 02 :Generated voltage when a EMI filter is inserted [V]*An attenuation of 20 [dB] means that the noise levelreduces to 1/10 of the one without an EMI filter.Similarly, 40 [dB] and 60 [dB] mean a 1/100 and1/1000 reduction of the noise level, respectively.Bas-RhinBas-RhinEMIBas-RhinBas-RhinFilterFigure 2.10.1 Attenuation CharacteristicMeasurement Method(Single-phase Normal Mode)Attenuation [dB]0102030405060708090100110120 0.1110100Frequency [MHz]Normal ModeCommon ModeFigure 2.10.3 Example of Attenuation Characteristic(NAC-16-472)The attenuation characteristic of EMI filters is affected bythe input and output impedances of a measured circuit.This attenuation characteristic (static characteristic) ismeasured under the constant condition of input andoutput impedances of 50regardless of measurementfrequencies. This enables the attenuation characteristicsof different filters to be compared under the sameconditions.However, actual electronic devices have different power lineimpedances, and impedance itself has its own frequencycharacteristic and does not take a constant value.For these reasons, the attenuation characteristics (staticcharacteristics) that are specified in the catalogs for EMIfilters do not necessarily coincide with those when theyare attached to actual electronic devices.One must also be careful that when connecting EMI filtersin series, the static characteristic of the resultant series isnot derived from simply adding the static characteristics[dB] of the individual filters.11Pulse Attenuation CharacteristicFigure 2.11.2 represents how much the EMI filter canattenuate pulse common mode noises, which may causemalfunctions of electronic equipment, connected to apower line. Figure 2.11.1 illustrates the measurementmethod.When terminating the input and output of the EMI filterwith 50 , and applying a specified pulse waveform onthe input, pulse voltages appearing on the outputare measured and plotted with the horizontal axis representinginput pulse voltage and with the vertical axisrepresenting output pulse voltage.NoiseSimulatorEMIFilterEMI/EMCFilterTechnical Notes-8EMIFilterFigure 2.10.2 Attenuation CharacteristicMeasurement Method(Single-phase Common Mode)? 766 ?Input palace waveformOutput pulse waveformFigure 2.11.1 Measurement Method forPulse Attenuation Characteristic(Single Phase)