Current Sources and Voltage References

54

Characteristics of the BJT

Under normal conditions, gain can be simply defined by the following:

where,

and therefore:

For example, let’s assume we have an ideal NPN transistor, with no leakage. If we

applied 10-µA current to its base and 1-mA current is induced to flow between its col-

lector to emitter, then the transistor would theoretically have a beta of 100. From equa-

tion 4.2 we can calculate this as shown in equation 4.5:

A standard test circuit for measuring the BJT’s gain is shown in Figure 4.5. Here two

current meters are used, which allow one to see the corresponding collector current,

for any particular applied base current.

While in ...