432 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



same rate as does Tc , the small signal collector impedance. Similar im- 

 provements have been made in these variations for switching transistors 

 and Fig. 24 is a series of graphs showing how the M1689 bead type 

 switching transistor changes the pulse characteristics defined in Fig. 20 

 with respect to temperature. For those switching functions examined 

 to date, it is believed that these data mean rehable operation to as high 

 as +70°C m most applications and perhaps as high as +80°C in others. 



3 

 2 



40 



70 



50 60 70 80 20 30 40 50 60 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 24 — Temperature behavior of the M1689 transistor. 



In junction transistors the laws of temperature variation are not so 

 well established, the device being in a much earlier stage of development. 

 Preliminary data indicate smaller variations in the small signal pa- 

 rameters such as a and Vc . On the other hand, variations in the dc cur- 

 rent, particularly Ico , are many times greater, of the order of 10 per 

 cent per degree centigrade.* The only saving grace here is the fact that 

 Ic« is normally very much less than the actual operating value of Ic . 



In summary, it may be said that while significant improvements have 

 been made in temperature dependence to the point where many appli- 

 cations appear feasible, it is not to be inferred that the temperature 

 limitation is completely overcome. Much more development work of 

 de\'ice, circuit and system nature is required to bring this aspect of 

 reliable operation to a completely satisfying solution. 



Shock and Vibration 



With regard to mechanical ruggedness, current point-contact tran- 

 sistors have been shock tested up to 20,000 g with no change in their 



leo is the collector current at zero emitter current. 



