CHOKES AND TRANSFORMERS 



the output waveform is distinctly non-sinusoidal, also they are rather large 

 for the power output they produce. 



Output 



Subsidiary 

 secondary 



o 



'"'''''-^^^::^, 



Figure 22.5 



SMOOTHING CHOKES 



These range in inductance from 5 h to 75 h, and in current from about 25 mA 

 max to 500 mA max, but it is necessary to point out that the low current 

 ratings tend to go with the high inductances and vice versa. A 75 h 500 mA 

 choke would be extremely large. The most usual values are 10 h and 20 h 

 at about 120 mA. In describing swinging chokes the inductance without 

 polarizing d.c, and with full d.c, are both quoted. 



b 



Figure 22.6 



a 



DESIGN OF SMALL AIR-CORED CHOKES 



Small inductances up to a few tens of millihenries may be made by winding 

 a simple coil of wire on some kind of bobbin of insulating and non-magnetic 

 material {Figure 22.6). The winding is then cylindrical and if a is the average 



308 



