Unformatted text preview:  I gen is small * Of course, I gen is large when the PN junction is close to or at breakdown.
Jason Woo 24 EE121B Spring 2010 We can write I C =M I nC I C = M 1 I nC i.e. , if VBC is not too large (much less than BVBC) Together, we have 0 = T M For advanced BJTs, 1  >> 1  T
1 1 i.e., >> 1  T 1
Therefore, Typically 0 = T M Jason Woo 25 EE121B Spring 2010 That is, J n ( 0) 0 = = 1  0 1  J p (  x E ) + J rec J n ( 0) DEWB N AB J p (  x E ) DBWE N DE if Jrec<< Jp(xE), i.e., JE is not too small Therefore, to maximize , we need to make WE NDE>>WB NAB (i.e., heavily doped the emitter). Note that in the low current regime when Jrec Jp(xE),
J n ( 0) 1 J rec = D B ni WB N AB W DBE rec e qVBE n 1 n kT can be rather small
Jason Woo 26 EE121B Spring 2010 At moderate current =
At high current, DBW E N DE constant DEWB N AB
 and I C n I n 1 n C  IC n Irec dominates IB VBC<0
 IC 1
*In
Jason Woo IC if the base reaches high level injection condition.
27 EE121B Spring 2010 reality, drops with large IC due to basepu...
View
Full Document
 Spring '09
 WANG
 Electromagnet, Transistor, Bipolar junction transistor, Jason Woo, EE121B Spring

Click to edit the document details