TRANSISTORS 



possible to attach some physical significance to the elements involved. 

 Thus Rg is the resistance of the emitter-base junction, which, being a diode 

 biased in the forward direction, is low (40 Cl in the transistor considered). 

 /?(. is the resistance of the base-collector junction, which is a diode biased in 

 the reverse direction, and is high (50 YQ). 7?^ is the resistance of the base 



Figure 45.11 



material between the external connection and the region between the 

 junctions and is intermediate (1 kQ). To explain the presence of the current 

 generator requires an explanation of transistor action, a perilous voyage 

 into the sea of semi-conductor physics which the author has no wish to 

 make. It is sufficient to take it that the transistor behaves as if there were 

 a current generator in the collector circuit of output fi times the base current. 



^h 



R. 



KTh 



Figure 45.12 



^ is closely related to A in the previous equivalent circuit and is numerically 

 close to it, between 20 and 60. Other symbols used for the quantity ^ are 



a' and a; 



6-c- 



/■& /in 





hi 



out 



'^c 



6K. 



Re 



6^'ou. 



1 



(a) 



(b) 



Figure 45.13 



It is not difficult to move between the two possible sets of transistor 

 parameters proposed so far. In Figure 45. 13a we have 



that is 

 and 



that is 



<5Kin = i?e-.(^/in + 5<5/out) 

 5 Kin -^ Re-Mn + Re-r>Bdh,, 



<5J^out = Re-X^hvLi — ^^An) 

 ^^^out = —Re-A^hn + Re-Mont 



682 



