0195136047.pdf

7.3 BIPOLAR JUNCTION TRANSISTORS 363

Collector current iC, mA

Saturation region

Linear

active region

Collector–emitter

voltage vCE, V

Increasing vBE

Breakdown

−(Early voltage)VA 0.6 to 0.8 V

Figure 7.3.5Early effect and Early voltage of typicalnpnsilicon BJT.

Ma

xim

um

coll

ecto

rdis

sipatio

n= (^30) W
Saturation region
0 − 10 − 20 − 30
−0.4
−0.8
−1.2
−1.6
−2.0 −
30
−^25
−^20
−^15
−^10
− 5
− 40 − 50
(Cutoff) Base current = 0 mA
− 60 − 70 − 80
Collector voltage, V
Collector current, A
Figure 7.3.6Common-emitter collector characteristics for typicalpnpBJT.
Despite the structural similarities, apnpBJT has smaller current gain than a comparablenpn
BJT because holes are less mobile than electrons. Most applications ofpnpBJTs involve pairing
them withnpnBJTs to take advantage of complementary operation. The large-signal models of
Figure 7.3.8 also hold forpnpBJTs if all voltages, currents, and battery polarities are reversed.
BJTs can provide the circuit properties of a controlled source or a switch.
+−vπ
= rπ ∆iB gmvπ
= β∆iB
∆iB ∆iC
∆iE
ro
B C
E
rπ
Figure 7.3.7Small-signal equivalent circuit of BJT.