TRANSISTORS IN" SWITCHING CIROUITS 



1245 



-0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 



EMITTER CURRENT, If , IN MILLIAMPERES 



Fig. 22 — Alpha characteristic. 



even though /•„, is zero since ay -^ {n/n + Tc). The vahies normally 

 encountered at /« = — A are usually in excess of this lower limit. 



The feedback resistance r^ tends to rise as /« — > which may be 

 important to some trigger circuits. As the circuitry becomes more 

 sophisticated, it is expected that more attention will need to be paid to 

 the behavior of r^ , r^ and n at and near /, = 0. 



The transition from Region II to Region III is determined from the 

 relation /« = —(Ic/a). The problem is quite similar to the control of 

 the M factor in tubes where plate current cut-off is given by Vg = 

 — (Vp/n). Present practice has been to depend upon the ai values and 

 upon the lower limit placed on alpha in the Vc(S, —5.5) measurement. 

 Further effort is needed here also. 



TYPICAL PARAMETER VALUES AND DISTRIBUTIONS 



Integrated distribution curves for the parameters of a typical develop- 

 mental switching transistor are shown in Fig. 23. The unit-to-unit 

 variations are deemed to compare favorably with those of commercial 

 electron tubes. The parameter of most serious vai'iability is r^o which is 

 unfortunate since Vco is so important to trigger sensitivity stability. 



TEMPERATURE, FREQUENCY AND SHOCK PROPERTIES 



Transistor parameters are reasonably constant with temperatures 

 below room temperature. Above room temperatures some of the param- 

 eters are variable, r^ and n are fairly constant, changing very little to 

 70°C. Vc and r^ decrease fairly rapidly, maintaining a ratio such that 

 alpha rises slightly, r^ and Tco change most I'apidly and, while both of 



