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Unformatted text preview: circuits provide motivation to
study dependent sources. DC Circuits These equations show that, in the active mode, the BJT can be modeled as
a dependent current-controlled current source. Thus, in circuit analysis,
the dc equivalent model in Fig. 3.40(b) may be used to replace the npn
transistor in Fig. 3.40(a). Since β in Eq. (3.32) is large, a small base
current controls large currents in the output circuit. Consequently, the
bipolar transistor can serve as an ampliﬁer, producing both current gain
and voltage gain. Such ampliﬁers can be used to furnish a considerable
amount of power to transducers such as loudspeakers or control motors.
IB C IC
B VCE +
VCE − − −
E E (a) (b) Figure 3.40 (a) An npn transistor, (b) its dc equivalent
model. It should be observed in the following examples that one cannot
directly analyze transistor circuits using nodal analysis because of the
potential difference between the terminals of the transistor. Only when
the transistor is replac...
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This note was uploaded on 07/16/2012 for the course KA KA 2000 taught by Professor Bkav during the Spring '12 term at Cambridge.
- Spring '12