0195136047.pdf

PROBLEMS 389

7.3.13If the circuit of Example 7.3.1 is to switch from
cutoff to saturation, find the condition onvS, given
that the transistor hasβ=100.

7.3.14Consider the circuit of Example 7.3.3. ForRE= 0
andβ=50, findiE.

7.3.15If the BJT in the circuit of Example 7.3.1 has
β=150, findiCandvCEwhen: (a)iB= 20 μA,
and (b)iB= 60 μA. Specify the state of the BJT
in each case.

7.3.16The circuit shown in Figure P7.3.16 has apnpBJT
turned upside down. FindRBwhenvEC=4 V and
β=25.

7.3.17Reconsider the circuit of Figure P7.3.16. With
β=25, find the condition onRBsuch thatiChas
the largest possible value.
7.4.1Consider JFET characteristics shown in Figures
7.4.3 (a) and (c).
(a) Write down the conditions for the operation
to take place in the active region.

(b) Obtain an expression for the drain currentiD

in the active region, and for the value ofiDfor

the boundary between the ohmic and active

regions.

(c) Find the conditions for the linear ohmic op-

eration and the equivalent drain-to-source re-

sistance.

(d) Express the condition for operation in the cut-

off region.

7.4.2The JFET with parametersVP=6 V andIDSS=

18 mA is used in the circuit shown in Figure P7.4.2

with a positive supply voltage. FindvGS,iD, and

vDS. Note that the gate current is negligible for the

arrangement shown.

*7.4.3Consider the circuit of Figure P7.4.2 with the

same JFET parameters. LetRSbe not specified.

DeterminevGS,vDS,andRSfor active operation at

iD=2 mA.

7.4.4A JFET withIDSS=32 mA andVP=5Vis

biased to produceiD=27 mA atvDS=4 V. Find

the region in which the device is operating.

RC

RF

VCC

+

Figure P7.3.12

C

B

E

+

+

−

+

−

−

RB

RC = 3 kΩ

vEB

vEE = 10 V

vEC

iC

Figure P7.3.16

D

S

+

G RD = 1.5 kΩ

RS = 250 Ω

VDD = 20 V

Figure P7.4.2