INDUCTANCES AND RESISTANCES 



which is closely related to the familiar B-H or hysteresis curve {Figure 4.38). 

 The permeabiUty is proportional to the slope of this, and is clearly not 

 constant if the flux is allowed to exceed a certain limit in either direction. 



Thus, for a given core, there is a definite allowable ^max if the linear 

 analysis is to remain true. For any transformer 



For a pulse transformer, e^ is a constant. Call it E. Then 



Therefore, if (f> is not to exceed ^max, Et must not exceed ^max f^s^i'-, that 

 is, there is an upper limit to the amplitude-duration product of pulse which 

 the transformer can transmit. 

 For a signal transformer, where the input is V cos cot 



d(f> V cos cot 

 d7 ^ K^Nj^ 



V sin cot 



cf>^ 



CO • K^N^ 



If cf) is not to exceed <^max» Vl^i must not exceed ^^ax ^1-^3- Hence, for 

 a given transformer fed with a given voltage, there is a lower frequency limit 

 below which the output waveform becomes distorted due to core saturation. 

 Matters can be improved again by reducing V. Since it is reasonable to fix 

 the frequency at which distortion begins at about the lower turn-over frequency 

 there will be associated with a particular transformer a maximum generator 

 voltage with which it can be used if the full band-width is to be available. 



In the case of power transformers, the voltages associated with the various 

 windings are those which, if exceeded, will cause core saturation. Saturation 

 in power transformers leads to very inferior efficiencies. 



71 



