FERRITE CORE INDUCTORS 



275 



600 

 500 



400 

 300 



200 



30 



10 20 30 40 60 80 100 200 300 400 600 1000 



Qo(Q FOR DISTRIBUTED CAPACITANCE = O) 



Fig. 3 — Effect of distributed capacitance on Q. 



maintain small values of distributed capacitance. It will be necessary 

 to increase the separation of windings from each other and from the 

 core and this will result in a lower winding efficiency and a higher dc 

 resistance. 



Since the limitations imposed by ac losses in the wire and by dis- 

 tributed capacitance depend on the absolute magnitudes of the design 

 parameters and the mechanical details of the inductor structure they 

 do not lend themselves to representation in practicable generalized for- 

 mulas as do the core losses. However, the following information on some 

 model inductors will illustrate the magnitudes of these Hmitations. 



A ferrite core coil was constructed similar to that shown in Fig. 4, 

 but having a core volume of only 0.04 cubic inches. It was a 5 mh coil 

 for use at 100 kc and had a distributed capacitance of 10 mmf. It was 

 wound with a single strand conductor and the winding efficiency, k^ , 

 was 0.4. Since it was intended for use at very low power levels the hystere- 

 sis loss was negligible. The permeability was optimized in accordance 

 with case 1, above, for residual loss predominating. The measured Q 

 was very close to 300. Thus, D = 0.0033. From the above data we note 

 that C/Cg = 0.02, and from (25) we can calculate that Do = 0.0030, 



