TRANSISTORS IN SWITCHING CIRCUITS 



289 



(Synopsis 

 •al 



Vb = hin + Rb+ >\ + R,) + I dr. + R,) 



] Vcc + IcXrc - r'c") = hir, + R, - r„) + 7,(r. + R. + R, - /•„.) 



(r. + RMr. + R. - rj^ 



rb + Rb + A'. + r. - 



r. + R. + rc + Re- r„. 



[\\c + Loir, - r'e")]{r, + R,) 



+ 



U + R,-\- rc+ Re- r„ 



).\iin;itc Short Circuit Case 



A', = R^ ^ (^ ■ I^Xtc - K") «C T'. ; r. «: red - «) 



n I 



n II 



n III 



Tc + r'J r; + Te 



n = /.i':^'U "•'■• 



\ — a I /•«(! — a) 





/bp ~ 



Vbp = 



1 - 



,,. = r.(,-^^i^) 



ince characteristic and properties. 



elusion is reached in the collector characteristic that the negative re- 

 sistance (Region II) is independent of the base resistance or fee(ll)ack. 

 This is true for only the limited range where r^ « Rb « Tc . 



EX.\MPLE OF CALCULATED AND EXPERIMENTAL CHARACTERISTICS 



An example to illustrate the analysis is shown in Fig. 20 where both 

 experimental and calculated characteristics for the emitter circuit are 

 given. In this example there is appreciable load resistance; hence Vc , 

 r't" and r^' are of no consequence since they will all be very small com- 

 pared to the Re of 2.2K ohms. Also, Rb = Q.SK ohms is much greater 

 than n ; hence n can be neglected. Since Vc is —45 volts, the Ico term 

 may also be neglected. 



