Power ferrites for high frequencies

Abstract

MnZn ferrites with Sn and/or Ti substitutions meet all main requirements for high frequency power applications. The composition Mn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0,631</inf> Zn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0,266</inf> Ti <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0,022</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0,010</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2,071</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> has been selected to demonstrate the advantages of these ferrites. By sintering under special conditions to a medium initial permeability of about <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu_{i} \approx 1500</tex> one achieves a flat μ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</inf> (ϑ)curve which varies only slightly up to 1 MHz in a wide temperature range. Thus contributions of gyromagnetic and dielectric losses are suppressed. The influence of eddy current power losses are discussed. They can only be reduced by high dc resistivity ρ, low magnetic flux density <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\circ{B}</tex> and small core sizes. The measurement of ρ versus temperature shows that with-in the application temperature range the decrease of ρ is governed by the same activation energy independent of the absolute value of ρ and the composition. Examples for power losses versus <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\circ{B}</tex> , frequency and temperature are given.