Current Sources and Voltage References

64

Characteristics of the BJT

Table 4.2 shows various collector currents and related V

BE

s based on this relationship

expressed in equation 4.23.

Table 4.2 The Relationship between V

BE

versus I

C

V

BE(sat)

is usually specified on a transistor’s data sheet at a particular base current

and collector current and can be measured as shown in Figure 4.15 (which is the

same circuit for testing V

CE(sat)

). For example, at 25˚C the popular 2N3904 NPN gen-

eral-purpose transistor has a V

BE(sat)

specification of 0.65 volt minimum to a maximum

of 0.85 volt, at a base current of 1 mA and a collector current of 10 mA. With a 5-mA

base current and a collector current of ...