Thus the gap length pops out ( in meters ). The formula in 2) makes this easy, as we know L and N, and Ae, Ur = 1 for air,
Ae / length of gap = L / N^2įor a gapped ferrite choke construction ( with litz for lowest AC losses ) - having determined all the parameters from 1) above - we now need to determine the gap in the ferrite ( to store nearly all the magnetic energy ) to give the required L for the turns. From the formula above - all else being equal, if you double the peak current required, Lmax can only be half what it was.ġc) Lmax is proportional to the size of the core ( cross sectional area Ae ).ġd) Lmax is proportional to the highest Bpk* you can safely run - this is limited again by dissipation of the core ( and the whole inductor ) which is constrained by the frequency of the flux swing(s) - if you sufficiently elevate the core temp the Bmax may fall and you enter saturation, so a full understanding of the data sheet for the core is of prime importance.Ģ) AL ( nH/N^2 ) = Uo.Ur. Multilayer windings and higher frequencies will introduce proximity effect and skin effect which will raise the Rac and hence limit the turns you can fit while keeping the hot spot temp of the inner part of the winding to a reasonable figure.ġb) Lmax is limited by the peak current you intend to run through the choke, as, Bpk is directly proportional to Ipk - and - if Ipk runs the core too close to saturation you will lose inductance.
( caveat - for a linear inductor )ġa) that is, the maximum L you can obtain from a given core ( & bobbin lets say ) is determined by how many turns you can fit on the bobbin, Nmax*, - this in turn is dictated by the rms current the winding has to carry ( and sometimes the peak current and sometimes the working insulation required by the volts per turn on the choke - and again by how effectively the heat can be got out of the winding ). However many engineers and similar don't have a quick and effective way to arrive at a design based on what they think they want. Power electronics is all about magnetics design - well a fair bit of it is.
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