FERRITE CORE INDUCTORS 269 



ment of the optimum permeability becomes an important step toward 

 achieving the desired coil performance. 



The first four of the "D's" in (3), dc resistance and the core losses, are 

 direct functions of the permeability and can be discussed to a certain 

 extent independently of the last two. 



The inductance of a magnetic core inductor is given by 



L = ^ (4) 



w^here k = constant 



N = number of turns in winding 



A — cross section of core 



■C = mean length of magnetic path through core. 



If the geometric proportions of the core have been prescribed, A 

 and t will bear a constant relationship to V^'^ and V^'^, respectively, and 

 (4) may be written 



L = hN'V"'ti (5) 



where h = constant 



V = core volimie. 



The dc resistance in the winding is 



where p = resistivity of the conductor 



X. = mean length of turn 



W = available area of cross section through which turns can be 

 linked with the core 



k^, = winding efficiency. This is the ratio of the actual cross 

 section of conductor to the available area, W. 



Again, for a core of given proportions (6) may be written 



7? - ^^' (7) 



