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Contents : HOME APPLICATION NOTES Design Guidelines for Iron Powder Cores * Maximum Ambient Temperature * Loss Distribution between Core & Copper * Temperature Rise of Magnetic Device * Thermal Conductivity of Core Material * Availability of Air Flow Static or Forced * Thermal Aging Considerations * Mechanical Mounting Precautions * Micrometals Design Software Disc 1 MICROMETALS INC. 5615 E. LA PALMA AVENUE ANAHEIM CALIFORNIA 92807-2109 USA Maximum Ambient Temperature Limits * Most applications for Iron Powder cores have a maximum ambient temperature of +55 C or less * Some designs are safe in a +70 C ambient provided Thermal Aging is considered and the life expectancy meets end of life goal for the product * The higher the ripple current in a specific design the lower the energy storage capability is for a given size core * As the % of Ripple Current increases the greater the core loss will become. A larger core lower permeability or a completely different core material may be necessary to assure longevity * Temperature Rise of the Magnetic component will set the maximum safe ambient temperature 2 MICROMETALS INC. 5615 E. LA PALMA AVENUE ANAHEIM CALIFORNIA 92807-2109 USA Loss Distribution between Core & Copper * A design dominated by core loss is not a prudent thing to do regardless of core material * As a starting point consider a 50-50 split between core and copper loss * A better design is on the order of 20-80 split between core and copper loss * Core loss is expressed in mW/cm of volume * Copper loss is expressed as I x Resistance * It is much easier to remove heat from the copper winding than from the core material 3 MICROMETALS INC. 5615 E. LA PALMA AVENUE ANAHEIM CALIFORNIA 92807-2109 USA Temperature Rise of the Magnetic Device * Assuming a +55 C ambient a good design practice to follow is +40 C temperature rise or less * This rule will keep UL and Product Safety people very happy * The design will have a built in safety margin which will tolerate abnormal overloads * Again reduce the core loss at the expense of the copper loss * A 25 C reduction in temperature will improve the life expectancy of the core by one order of magnitude 4 MICROMETALS INC. 5615 E. LA PALMA AVENUE ANAHEIM CALIFORNIA 92807-2109 USA Thermal Conductivity of Various Materials Material Mix No. -2 -8 -10 -17 -18 -26 -28 -33 -40 -52 -0 Permeability i Thermal Conductivity mW/cm C 10 35 6.0 4.0 55 75 22 33 60 75 1.0 10.8 29.9 10.3 13.3 21.2 42.6 16.3 20.2 34.0 34.0 5.6 Approximate Values of Other Materials for Reference Material Description Thermal Conductivity mW/cm C Aluminum Solid Iron Ferrite 450 120 10 5 MICROMETALS INC. 5615 E. LA PALMA AVENUE ANAHEIM CALIFORNIA 92807-2109 USA

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