1228 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



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voltages are of the order of several milliamperes and a few volts, Ico 

 and Fco naay normally be neglected, /co and V^ do have considerable 

 interest to the device designer, however. The net circuit interpretation 

 of /ro and Fco is to effectively transfer the current-voltage axis from 

 0, to lea , Vco . Therefore, 



Vc - Vco = R2lh + (/c - /co)/?22 (10) 



or 



Vc - FcO = (jm + n)h + He - Ico) (re + V,) (H) 



Making the approximation that Vco = /co/?22 and rearranging, equa- 

 tion (10) becomes, 



or 



Vc — IcoRii + IdaR-22 = Riil( + IcRi 



Ve + /co(i?22 - R22') = R21L 4- TcR22 



(12) 



(13) 



which is of the usual form except that a small dc generator of magnitude 

 Ico{R22 — R22 ) has been added in series with the collector. Since R22 = 

 Tc + n and R22 = r'o' + n , 



Ico{R22 - R'22) = Icoirc - r'/') (14) 



The output family equation with equivalent circuit parameters is 



(collector VOLTAGE 

 SATURATION) 



Fig. 15 — Idealization and regional divi.sion of output characteristic (Rn)- 



