PRINCIPLES OF TRANSISTOR ACTION 



257 



same reason, it is expected that g(s) will be relatively independent of Vc- 

 This was indeed found to be true in this particular case and the values 

 r,- = —5, —10, and —15 were used in Figure 9 which gives a plot of g 

 versus 5 for several values of h. The dotted lines give the extrapolation 

 to 5 = 0. As expected, g increases with h for a fixed s. The different 

 cur\^es can be brought into approximate agreement by taking s/Ic as the 

 independent variable, and this is done in Fig. 10. As will be discussed in 

 Section \', such a relation is to be expected if g depends on the transit time 

 for the holes. 



\\\RIATION WITH TEMPERATURE 



Only a limited amount of data has been obtained on the variation of 

 transistor characteristics with temperatures. It is known that the reverse 



< 1.56 



< (.0^ 



2 0.5 



§ -50 -40 -30 -20 -10 10 20 30 



^ TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 11— Current amplification factor a vs. temperature for two experimental units 

 A and B. 



characteristic of the germanium diode varies rapidly with temperature, 

 particularly in the case of units with high reverse resistance. In the tran- 

 sistor the collector is electrically formed in such a way as to have relatively 

 low reverse resistance, and its characteristic is much less dependent on 

 temperature. Both 7^22 and Rn decrease with increase in T, R^z usually 

 decreasing more rapidly than Ru. The feedback resistance, Rn, is rela- 

 tively independent of temi)erature. The current multiplication factor, a, 

 increases with temperature, but the change is not extremely rapid. Figure 

 11 gives a plot of a versus T for two experunental units. The d-c. bias 

 currents are kept fixed as the temperature is varied. The over-all change 

 in a from -50°C to +50°C is only about 50 per cent. The increase in a 

 with T results in an increase in power gain with temperature. This may be 

 nullified by a decrease in the ratio Rii/Rn, so that the over-all gain at fixed 

 bias current may have a negative temperature coefficient. 



