title: COSEL Power Supply, Noise Filter 2025 Product Catalog

Summary

COSEL Power Supply, Noise Filter 2025 Product Catalog

2Selection of EMI Filters1 Rated Voltage3 Test Voltage (Withstand Voltage)The rated voltage is the maximum line voltage(nominal value) allowable to be used.As the rated voltages for some parts used within anEMI filter are high in reality, however, voltages higherthan the rated voltage of the EMI filter may be usedwithout causing any trouble.In fact, the rated voltages of filter components areoften higher, in which case the filter can handle actualvoltages that exceed its ratins.In the case of some EMI filters, the maximum operationvoltages are defined by specifications for them,separately from rated voltages.Note that using EMI filters at voltages lower than theirrated voltages do not pose any problems. Forexample, an EMI filter with a rated voltage of AC 250 Vcan be used for power lines of AC 100V.As for line frequency, EMI filters for AC power supplylines have been basically designed to be used with thecommercial frequency (50 Hz/60 Hz).Higher frequencies such as 400Hz can causeproblems such as excessive capacitor heating.Note that EMI filters for AC power lines can also beused for DC power supply lines.The rated current is the maximum load current(nominal value) that can be continuously carried. If theambient temperature is high, however, the load currentneeds to be derated.Figure 2.2.1 shows an example of a derating characteristic.Load factor[%]210080604020Rated Current0-40-30-2040505560708090Ambient air temperature[]Figure 2.2.1 Derating CurveThis example indicates that when the maximum ambienttemperature reaches 75 , the EMI filter should be usedwith a load factor of approximately 60% (approximately60% of the rated current) or lower.Current higher than the rated current would be allowed toflow in EMI filters for a short period of time only. Inrushcurrent (Up to 40A or 10 times the rated current, singleshots with a length of a few milliseconds) from devicessuch as a general switching power source does not causeany problems, but relatively long and / or repetitive peakcurrent draws can result in the average current exceedingthe filter’s raring.The test voltage is a voltage value that is applied atthe time of withstand voltage test. The withstandvoltage test is to verify that the part does not breakwhen applying a high voltage in a short period of timebetween a terminal (line) and the mounting plate(ground) of an EMI filter.In the case of EMI filters for AC power lines, the testvoltage is generally AC 2000 V or AC 2500 V.In withstand voltage tests, the high voltage appliedbetween a line and ground, results in abnormally highleakage current flow. When carrying out a withstandvoltage test in an acceptance inspection, please setthe cutoff current of withstand voltage test equipmentto an appropriate value (the cutoff current defined inthe specifications for the EMI filter).For some EMI filters that have ground capacitors withextremely large capacity, DC voltages may be used fortest voltages because the leakage current becomestoo high when AC voltages are applied.4Insulation Resistance (Isolation Resistance)Insulation resistance is a resistance value when applyinga specified DC voltage (normally 500 V) betweenisolated conductors such as a terminal (line) and themounting plate (ground), and regarded as one indicatorof degree of insulation.The insulation resistance is found by measuring thevery small current that flows in an insulating materialsuch as a resin case and capacitor when DC voltage isapplied.5Leakage CurrentThe leakage current is an electric current that flowsfrom the ground terminal of an EMI filter when thefilter is connected to an AC power line.Generally, as one sets the capacitance of a groundcapacitor to a higher value, the reduction effect oncommon mode noise will be heightened and at thesame time, the leakage current will increase.Care must be taken, because large leakage currentcould cause a circuit breaker to trip or electric shockto occur when the EMI filter is not properly grounded.Current ( ) that flows from each power line to groundis represented with the following expression; it formsthe basis of leakage current calculation.f : Power frequencyC : Capacitance between lineand groundE : Power supply voltagebetween line and groundEMI/EMCFilter? 763 ?Technical Notes-5