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Appendix D

Magnetics Design Tables

Geometritiil data for several staiidiird ferrite core shapes iire lisled here. The geometrical con.4tant is a ineasure of core size, useful for designing inductors and transformers that attain a given copper loss [1]. The method for indnctor design is described in Chapter 14. is defined as

(П,1)

where A. is the core cross-sectional area, is the window area, and MLTk the winding inean-length-per-tuin. The geometiicaJ constant K, is a similar measure of core size, which is useful for designing ac inductors and transformers when the total copper plus core loss is constrained. The K, method for magnetics design is described in Chapter 15. K is defined as

W J го - i/w

where is the core mean magnetic path length, and P is the core loss exponent: For modem ferrite materials, p typically lies in the range 2.6 to 2.8. Thequantity u(P) is defined as

<D.2)

(D.3}

2 1

1 + n 1

(D.4)

u(ff)h equal to 0J()5 for p = 2,7. This quantity varies by rouglily 5% over the range 2.6 <fi< 2.8. Values of iCj are tabulated for P = 2.7; variation of АГ, over the range 2.6<P<2.8 is typically quite small.

Thermal resistances are listed in those cases where published manufacturers data are available. The thermal resistances listed are the approximate temperature rise from the center leg of the core to ambient, per watt of total power loss, Different temperature rises may he observed under conditions of forced air cooling, unusual power loss distributions, etc. Listed window areas; are the winding areas for conventional single-section bobbins.

An American Wire Gauge table is included at the end of this appendix.

POT CORE DATA

Fig. D.1