0195136047.pdf

386 SEMICONDUCTOR DEVICES

D 1

vL

RL

D 3

D 4

D 2

vS(t) = VS sin ωt

+ +−

−

Figure P7.2.30

RL vL(t)

V 2

D 2

−

+

V 1

RS

Source Limiter Load

D 1

+

−

vS(t)

+

−

+

−

Figure P7.2.31

E

B

C

+

−

430 kΩ 4.7 kΩ

12 V

Figure P7.3.6

*7.3.7Using the small-signal equivalent circuit of a BJT
withgm= 0 .03 S,β=75, andVA=65 V, a load
resistorRLis connected from the collector to the
emitter, as shown in Figure P7.3.7. The transistor
is biased to have a dc collector current of 6 mA.
(a) Calculate vLdue to the small change vBE.
(b) Find the corresponding change iB in the
base current.
7.3.8The common-emitter configuration shown in Fig-
ure P7.3.8(a) for apnpBJT is most frequently used
because the base current exerts a greater control on
the collector current than does the emitter current.
The idealized collector characteristics of thepnp
transistor are shown in Figure P7.3.8(b) along with
the load line.

The main power sourceVCCin conjunction

with the base-bias sourceIBBis used to establish

the operating pointQin Figure P7.3.8(b). Let the

controlling signal beib=

√

2 Ibsinωt. Sketch

the sinusoidal variations of collector currentiC,

collector voltagevC, and base currentiB, super-

imposed on the direct valuesICQ,VCQ,andIBQ,

respectively, and calculate the current gain corre-

sponding to a change in base current of 10 mA

(peak value).

7.3.9(a) A simple circuit using annpnBJT containing

only one supply is shown in Figure P7.3.9(a).

Outline a procedure for determining the oper-

ating pointQ. The collector characteristics of

the transistor are given in Figure P7.3.9(b).