PROPERTIES AND APPLICATIONS OF n-p-fl TRANSISTORS 545 



To achieve this step-up would require a load impedance very large com- 

 pared to 13 megohms, but even with more modest values of load impedance 

 the voltage step-up is large. 



If Rl is small compared to Tc , the second of equations (7) leads to 



(19) 



= —ii 



and the current delivered to the load is approximately equal to the current 

 which the generator delivers to the transistor. 



From equations (10) and (11), the input and output impedances are 



R< = r. + r. - '•^1%+:^^ (20) 



i?, = r. + r. - ''t" Vi (21) 



Te -r n -{- Rg 



As the load impedance varies from zero to infinity, the input impedance 

 varies from 



Ri = re-\-n\\- 'i^L+J}] for R^ = 



^u + n{l - a) ^^^^ 



= 31.1 ohm 

 to 



R. = re + Tb = 266 ohms for Rl= ^. (23) 



When Rg = 0, the output impedance is 



Ro = U- -^ (fm - fe) (24) 



Te -f- n 



Te + n (25) 



= 1.56 (10)' ohms. 

 As Rg increases to infinity 



Ro= rc-\-H= 13.4 (10)« ohms. (26) 



