FERRITE CORE INDUCTORS 



273 



0.6 

 0.5 



0.3 



0.2 



0.2 0.3 0.4 0.6 0.8 1.0 



VOLUME 



3 4 5 6 8 10 



Fig. 2 — Relationship between core volume and dissipation factor. 



deviations from optimum up to about 20 per cent the penalty in dis- 

 sipation is not severe, but beyond this point the dissipation factor in- 

 creases rapidly. 



EFFECT OF VOLUME ON DISSIPATION FACTOR 



It has been shoTVTi in the preceding section that the permeabiUty can 

 be adjusted for optimum coil quality but that the value to which it is 

 adjusted depends on which of the loss factors predominates. It will also 

 be seen from the foregoing that both the value of optimum permeability 

 and the dissipation factor that can be realized by so adjusting the per- 

 meability depend on the volume of the core. The curves of Fig. 2 are 

 derived from (17), (20) and (23), respectively, considering Dopt- as a 

 function of the independent variable, V. That is, they show how the 

 dissipation factor will vary as a function of volume assuming that the 

 permeability is adjusted as the volume is changed so that the lowest 

 possible dissipation factor is always realized. 



As would be expected, these curves show that, regardless of the rela- 

 tive magnitudes of the core losses, the dissipation factor can be decreased 

 by increasing the size of the coil. There are serious hmitations, however, 

 on how far this process can be carried, and these are due to Dc and D, , 

 the resistive components resulting from capacitance and ac loss in the 

 wire. 



