0195136047.pdf

384 SEMICONDUCTOR DEVICES

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9 V 300 Ω 100 Ω

iD

600 Ω Diode

Figure P7.2.16

v(t) vo(t)

v(t)

t

600 Ω

6 V

0 10 mS

200 Ω 10 V

Ideal diode

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− −

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Figure P7.2.17

V 2

R 2

i

v = 5 V R 3

3.5 V

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− −

V 1

R 1

2 V

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−

Figure P7.2.18

5 V

vd = 5 + 0.01 sin ωt − RSid

vS(t) = VS sin ωt RS^ =^1000 Ω id

= 0.01 sin ωt

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−

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−

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Figure P7.2.19

7.2.20(a) In the circuit shown in Figure P7.2.20, the
zener diode (with zero zener resistance) op-
erates in its reverse breakdown region while
the voltage across it is held constant atVZ
and the load current is held constant atVZ/RL,
as the source voltage varies within the limits
VS,min <VS <VS,max. FindImaxandImin
for the correspondingRminandRmax, respec-
tively.

(b) AssumingRS =0 and the source voltage

to vary between 120 and 75 V, for a load

resistance of 1000, determine the maximum

value of the regulator resistorRif it is desired

to maintain the load voltage at 60 V. Also find

the required power rating of the zener.

7.2.21For the zener diode regulator of Figure P7.2.20,

assuming thatVSvaries between 40 and 60 V, with

RS= 100 andRL=1k, select a zener diode

and its regulator resistor such thatVLis maintained

at 30 V. You may assume zero zener resistance.

7.2.22ChooseRand find the smallest load resistance

allowed in Figure P7.2.20 whenVZ=12 V and

the source is 25 V±20% withRS=0. Assume

a maximum desired diode current of 20 mA and a

minimum of 1 mA.

*7.2.23Two zener diodes are connected as shown in Fig-

ure P7.2.23. For each diodeVZ=5 V. Reverse

saturation currents are 2μA forD 1 and 4μA for

D 2. Calculatev 1 andv 2 : (a) whenVS=4V,and

(b) ifVSis raised to 8 V.