TRANSISTORS I.V SWITCHING CIRCUITS 



1243 



In junction devices the proper measurements would he of /^o and fc . 

 Since /dt is difficult to define in point contact devices, Tco has been 

 measured as an ap{)i-o.\imation. In the idealization, r^ and r^i arc re- 



lated as, 



. Uc - Ico) 



>M = = 1\ 



im 



The measiu'ement of 7-^0 is made at a collector voltage which is typical 

 of the applications in the range of perhaps —10 to —45 volts. 



A constant dissipation line has been drawn on Fig. 21, which reveals 

 the desirability of having Vco very large in order to operate at higher 

 voltages and to secure high efficiency through lower dissipation in the 

 OFF or rest condition. 



UEGIOX II PROPERTIES 



The Region II low frequency properties are essentially identical to 

 those of transistors intended for small-signal applications. A possible 

 exception is the somewhat less attention paid to the base resistance, n , 

 which is critical to small-signal applications. The characterization con- 

 sists of a normal small-signal set plus dc bias values. 



UEGIOX III PROPERTIES 



The Region III properties have been defined largely by a figure of 



Ir_= -5.5 MA 

 COLLECTOR CURRENT 



r^= 



Vc CONSTANT 



CONSTANT 



DISSIPATION 



Fig. 21 — Idealized output characteristic illu.strating parameters. 



