Deck 3: Special-Purpose Diodes

Question 1

Refer to e)in the figure above. The symbol is for

A)a zener diode.
B)an LED.
C)a Schottky diode.
D)a photodiode.
E)a tunnel diode.

Answer 1

C

Question 2

The varactor is usually

A)operated in the breakdown region.
B)reverse- biased.
C)unbiased.
D)forward- biased.

Answer 2

B

Question 3

Refer to a)in the figure above. The symbol is for

A)a zener diode.
B)an LED.
C)a Schottky diode.
D)a photodiode.
E)a tunnel diode.

Answer 3

B

Question 4

LED color is determined by

A)the impurities added during doping to control wavelength.
B)the LED current.
C)the material used for the incandescent filament.
D)the applied LED voltage.

Question 5

All of the following are characteristics of a laser diode except

A)contains a pn junction.
B)emits light of a single color.
C)emits incoherent light.
D)emits monochromatic light.

Question 6

Two types of reverse breakdown in a zener diode are

A)avalanche and forward.
B)charge and discharge.
C)avalanche and zener.
D)avalanche and reverse.

Question 7

A _ _ diode maintains a constant voltage across it when operating in the breakdown condition.

A)silicon
B)zener
C)germanium
D)None of the above.

Question 8

When a zener diode is forward- biased, it

A)exhibits a voltage drop of VZ + 0.7 V.
B)conducts no current.
C)emits visible light.
D)operates like a rectifier diode.

Question 9

A Schottky diode is a diode that

A)varies its resistance with temperature.
B)changes its capacitance with voltage.
C)emits light when forward- biased.
D)switches very fast.
E)exhibits an increase in reverse current with light intensity.

Question 10

An LED is forward- biased. The diode should be on, but no light is showing. A possible problem might be

A)that the power supply voltage is too high.
B)that the series resistor is too small.
C)none; the diode should be off if forward- biased.
D)that the diode is open.

Question 11

Refer to c)in the figure above. The symbol is for

A)a zener diode.
B)an LED.
C)a Schottky diode.
D)a photodiode.
E)a tunnel diode.

Question 12

Refer to the figure above. If Vin increases, VR will

A)increase.
B)remain the same.
C)decrease.
D)Unable to determine.

Question 13

The band gap of a quantum dot is dependent on

A)the size of the dot.
B)its color.
C)the dot polarity.
D)its frequency.

Question 14

Which of the following has a negative- resistance region?

A)Rectifier diode
B)Schottky diode
C)Tunnel diode
D)LED

Question 15

A tunnel diode has _ characteristics).

A)a negative resistance
B)extremely light doping
C)a linear
D)an extremely wide depletion region

Question 16

Quantum dot filters are used to

A)focus LEDs for fiber optic systems.
B)limit bandwidth.
C)make white LEDs look more like incandescent lights.
D)increase the blue content of an LED lighting system.

Question 17

The correct way to illuminate an LED is to

A)place the LED in series with a resistor and a 5 V dc supply with the anode toward the positive side of the supply.
B)place the LED in series with a resisitor and a 5 V dc supply with the cathode toward the positive side of the supply.
C)place the LED in forward bias directly across a 5 V dc supply.
D)place the LED in reverse bias directly across a 5 V dc supply.

Question 18

The capacitance of a varactor diode

A)decreases as the reverse bias voltage increases.
B)remains constant as the bias voltage varies.
C)increases as the reverse bias voltage increases.
D)is usually 1000 µF or more.

Question 19

To display the digit 8 in a seven- segment indicator

A)only C must be lighted.
B)only F must be on.
C)G must be off.
D)all segments must be on.

Question 20

A varactor is a diode that

A)varies its resistance with temperature.
B)changes its capacitance with voltage.
C)emits light when forward- biased.
D)switches very fast.
E)exhibits an increase in reverse current with light intensity.

Question 21

When the source voltage increases in a zener regulator, the current that remains approximately constant is the

A)total current.
B)series current.
C)zener current.
D)load current.

Question 22

Refer to the figure above. If the load current increases, IR will and IZ will .

A)remain the same, increase
B)increase, remain the same
C)decrease, remain the same
D)remain the same, decrease

Question 23

A photodiode is normally

A)forward- biased.
B)not biased.
C)used to regulate voltage.
D)reverse- biased.

Question 24

A diode with a negative- resistance characteristic is needed. The correct selection would be a

A)Gunn diode.
B)tunnel diode.
C)varactor diode.
D)Schottky diode.

Question 25

An OLED produces light by a process called

A)avalanche light emission.
B)electrophosphorescence.
C)photonic light emission.
D)organic light emission.

Question 26

The PIN diode, when reverse- biased, acts like a nearly constant

A)current source.
B)capacitance.
C)resistance.
D)voltage source.

Question 27

Refer to d)in the figure above. The symbol is for

A)a zener diode.
B)an LED.
C)a Schottky diode.
D)a photodiode.
E)a tunnel diode.

Question 28

Refer to the figure above. As long as the zener is in regulation,

A)there is no current through the zener.
B)VRL will be equal to 0.7 V.
C)there is no current through RL.
D)the current IRL)remains constant.

Question 29

Refer to the figure above. Measurements show that VRL has increased. Which of the following faults, if any, could have caused this problem?

A)The zener opens.
B)Vin has decreased.
C)The zener shorts.
D)R opens.

Question 30

Data sheets for zener diodes usually specify the zener voltage at a particular test current designated

A)IZT.
B)IS.
C)IZK.
D)IZM.

Question 31

If the load resistance decreases in a zener regulator, the series current

A)decreases.
B)equals the source voltage divided by the series resistance.
C)stays the same.
D)increases.

Question 32

When the light increases, the reverse minority carrier current in a photodiode

A)reverses direction.
B)decreases.
C)increases.
D)is unaffected.

Question 33

A Schottky diode

A)has a metal- to- semiconductor junction.
B)cannot operate properly at high frequencies.
C)has no limit on maximum current.
D)has a forward voltage drop of about 2 V.

Question 34

A 6.2 V zener is rated at 1 watt. The maximum safe current the zener can carry is approximately

A)16.1 mA.
B)1.61 A.
C)1.61 mA.
D)161 mA.

Question 35

Typically, the maximum VF for an LED is between

A)1 V and 1.4 V.
B)0 V and 0.7 V.
C)1.2 V and 3.2 V.
D)3.2 V and 10 V.

Question 36

What is true about the breakdown voltage in a zener diode?

A)It is approximately constant.
B)It destroys the diode.
C)It decreases when current increases.
D)It occurs only in the forward region.

Question 37

Modern traffic signals and large video screens are implemented with

A)hot filament bulbs.
B)infrared photodiodes.
C)PIN diodes.
D)high intensity LED arrays.

Question 38

If the load resistance decreases in a zener regulator, the zener current

A)decreases.
B)stays the same.
C)equals the source voltage divided by the series resistance.
D)increases.

Question 39

A photodiode is a diode that

A)varies its resistance with temperature.
B)changes its capacitance with light intensity.
C)emits light when forward- biased.
D)switches very fast.
E)exhibits an increase in reverse current with light intensity.

Question 40

Refer to the figure above. If Vin decreases, IR will

A)remain the same.
B)increase.
C)decrease.
D)Unable to determine.

Question 41

Refer to the figure above. If the load current increases in the zener regulator,

A)the zener current increases.
B)the series current increases.
C)the series current remains the same.
D)Both B and C above.

Question 42

For zener diodes, the temperature coefficient is

A)negative for breakdown voltages less than 5 V and positive for breakdown voltages greater than 6 V.
B)always zero.
C)always negative.
D)always positive.

Question 43

The best type of diode to use in a tuning circuit is

A)a Schottky diode.
B)a varactor.
C)an LED.
D)a Gunn diode.

Question 44

The radiation pattern for an LED

A)shows how directional the light is.
B)shows the wavelength of the light.
C)visually shows the color of the light.
D)shows the current vs. voltage curve of the LED.