Electronics Devices and Circuits 1

Figueroa, Raed A. August 31, 2010

B.S. CpE Engr. Jason Rex H. Agustin

SELF-TEST CHAPTER 3

1. The cathode of a zener diode in a voltage (b) senses light when reverse-biased
regulator is normally (c) emits light when forward-biased
(a) more positive than the anode (d) acts as a variable resistance
(b) more negative than the anode
(c) at +0.7 V 8. Compared to a visible red LED, an infrared
(d) grounded LED
(a) produces light with shorter wavelengths
2. If a certain zener diode has a zener voltage of (b) produces light of all wavelengths
3.6 V, it operates in (c) produces only one color of light
(a) regulated breakdown (d) produces light with longer wavelengths
(b) zener breakdown
(c) Forward conduction 9. Compare to incandescent bulbs, highly
(d) avalanche breakdown intensity LED’s
(a) are brighter
3. For a certain 12 V zener diode. a 10 mA (b) have a much longer life
change in zener current produces a 0.1 V change (c) use less power
in zener voltage. The zener impedance for this (d) all of the above
current range is
(a) 1 (b) 100 10. An OLED differs from a conventional LED in
(c) 10 (d) 0.1 that it
(a) requires no bias voltage
4. The data sheet for a panicular zener gives Vz = (b) has layers of organic material in the place of
10 V at Iz = 500 mA. Zz for these conditions is a pn junction
(a) 50 (b) 20 (c) can be implemented using an inkjet printing
(c) 10 (d) unknown process
(d) both (b) and (c)
5. A no-load condition means that
(a) the load has infinite resistance 11. An infrared LED is optically coupled to a
(b) the load has zero resistance photodiode. When the LED is turned off, the
(c) the output terminals are open reading on an ammeter in series with the
(d) answers (a) and (c) reverse-biased photodiode will
(a) not change
6. A varactor diode exhibits (b) decrease
(a) a variable capacitance that depends on (c) increase
reverse voltage (d) fluctuate
(b) a variable resistance that depends on reverse
voltage 12. The internal resistance of a photodiode
(c) a variable capacitance that depends un (a) increases with light intensity when reverse-
forward current biased
(d) a constant capacitance over a range of (b) decreases with light intensity when reverse-
reverse voltages biased
(c) increases with light intensity when forward-
7. An LED biased
(a) emits light when reverse-biased (d) decreases with light intensity when forward-
biased
13. A laser diode produces 5. For normal operation of a pnp transistor, the
(a) incoherent (b) cohorent base must be (+ or - ) with respect to the
(c) monochromic light (d) both (b) and (c) emitter, and ( + or -) with respect to the
collector.
14. A diode that has a negative resistance
characteristics is the Ans. The base must be negative with respect ti
(a) Schottky diode the collector and positive with respect to the
(b) tunnel diode emitter.
(c) laser diode
(d) hot-carrier diode 6. What is the value of Ie for IE = 5.34 mA and IB
= 475 A?
15. In order for a system to function properly,
the various types of circuits that make up the Ans. IC = IE – IB = 5.34 mA – 475 A = 4.87 mA
system must be
(a) properly biased 7. What is the when IC = 8.23 mA and IE =
(b) properly connected 8.69 mA?
(c) properly interfaced
(d) all of the above Ans.
(e) answers (a) and (b)
8. A certain transistor has an IC = 25 mA and an
PROBLEMS CHAPTER 4 IB = 200 A. Determine the . .

1. What are the majority carriers in the base Ans.

region of an npn transistor called?
9. What is the of a transistor if IC = 20.3 mA
Ans. Majority carriers in the base region of an and IE = 20.5 mA?
npn transistor are holes.
Ans.
2. Explain the purpose of a thin, lightly doped
base region.

Ans. Because if the narrow base region, the

minority carriers invading the base region find a 10. What is the if IE = 5.35 mA and IB = 50
limited number of partners for recombination A?
and, therefore, move across the junction into
the collector of region rather than out of the Ans.
base lead.

3. Why is the base current in a transistor so 11. A certain transistor exhibits an of 0.96.
much less than the collector current? Determine IC when IE = 9.35 mA.

Ans. The base is narrow and lightly doped so Ans.

that a small recombination (base) current is
generated compared to the collector current. 12. A base current of 50 A is applied to the
transistor in Figure 4-53. and a voltage of 5 V is
4. In a certain transistor circuit, the base current dropped across Rc. Determine the of the
is 2 percent of the 30 mA emitter current. transistor.
Determine the collector current.
Ans.
Ans. IB = 0.02IE = 0.02(30 mA) = 0.6 mA
IC = IE – IB = 30 mA – 0.6 mA = 29.4 mA
13. Calculate for the transistor in Problem 12. Ans.

Ans.
22. A certain transistor is to be operated at a
collector of 50 mA. How high can VCE go without
14. Assume that the transistor in the circuit of Figure exceeding a PD(max) of 1.2 W?
4-53 is replaced with one having a of 200.
Determine IB, IC, IE and VCE given that VCC = 10v and Ans.
VBB = 3v.

Ans. 23. The power dissipation derating factor for a

certain transistor is 1 mW/C. The PD(max) is 0.5 W at
25C. What is PD(max) at 100C?
15. If VCC is increased to 15v in Figure 4-53, how
much do the currents and VCE change? Ans.

Ans.
24. A transistor amplifier has a voltage gain of 50.
What is the output voltage when the input
16. Determine each current in Figure 4-54. What is voltage is 100 mV?
the ?
Ans.
Ans.

25. To achieve an output of 10 V with an input of 300

17. Find VCE, VBE and VCB in both circuits of Figure 4- mV, what voltage gain is required?
55.
Ans.
Ans.

26. A 50 mV signal is applied to the base of a

18. Determine whether or not the transistors in properly biased transistor with r’e = 10 and Rc =
Figure 4-55 are saturated. 560 . Determine the signal voltage at the collector.

Ans. Ans.

19. Find IB, IE and IC in Figure 4-56. = 0.98. 27. Determine the value of the collector resistor in
an npn transistor amplifier with = 250, VBB =
Ans. 2.5v, VCC = 9v, VCE = 4v and RB = 100 .

Ans.
20. Determine the terminal voltages of each
transistor with respect to ground for each circuit in
Figure 4-57. Also determine VCE, VBE and VCB. 28. What is the DC current gain of each circuit in
Figure 4-55?
Ans.
Ans.

21. If the in Figure 4-57(a) changes from 100 to

150 due to a temperature increase. What is the 29. Determine for the transistor in Figure 4-
change in collector current? 58. What is the value of IB necessary to produce
saturation? What minimum value of VIN is necessary
for saturation? Assume VCE(sat) = 0 v.

Ans.

30. The transistor in Figure 4-59 has a of 50.

Determine the value of RB required to ensure
saturation when VIN is 5 V. What must VIN be to cut
off the transistor? Assume VCE(sat) = 0 v.

Ans.

31. A certain phototransistor in a circuit has a =

200. If I = 100 A., what is the collector current?

Ans.

32. Determine the emitter current in the

phototransistor circuit in Figure 4-60 if, for each
1m/m² of light intensity. 1 A of base current is
produced in the phototransistor.

Ans.

33. A particular optical coupler has a current transfer

ratio of 30 percent. If the input current is 100 mA,
what is the output current?

Ans.

34. The optical coupler shown in Figure 4-61 is

required to deliver at least 10 mA to the external
load. If the current transfer ratio is 60 percent, how
much current must be supplied to the input?

Ans.

35. Identify the leads on the transistors in Figure 4-

62. Bottom views are shown.

Ans.

36. What is the most probable category of each

transistor in Figure 4-63?

Ans.