Deck 17: Voltage Regulators

Question 1

The 7912 produces a regulated output voltage of

A)+12 V.
B)+5 V.
C)- 12 V.
D)+9 V.

Answer 1

C

Question 2

Refer to the figure above. This circuit is brought in for repair. The measured output voltage was 25 V under all load conditions. A possible cause of this symptom might be that

A)R3 has opened.
B)R2 has opened.
C)Q1 base- emitter has opened.
D)Vin has decreased.

Answer 2

B

Question 3

Switching regulators have than linear regulators.

A)more heat- sinking requirements
B)simpler circuitry
C)greater efficiency
D)lower efficiency

Answer 3

C

Question 4

is a measurement of how well the power supply maintains a constant output voltage with changes in input voltage.

A)Load voltage control
B)Load regulation
C)Line regulation
D)Voltage control

Question 5

A voltage regulator with a no- load output dc voltage of 12 V is connect to a load with a resistance of 10 ▲. If the load resistance decreases to 7.5 ▲, the load voltage will decrease to 10.9 V. The load current will be and the percent load regulation is .

A)1.45 A, 10.09%
B)1.6 A, 90.8%
C)1.6 A, 9.17%
D)1.45 A, 90.8%

Question 6

A 7805 regulator has a +20 V input. If the input and output pins of the regulator are shorted together by a solder bridge, the output voltage will be

A)0.7 V.
B)+20 V.
C)+5 V.
D)0 V.

Question 7

A _ _ maintains a constant output voltage by controlling the duty cycle of a switch in series with the load.

A)shunt regulator
B)linear regulator
C)switching regulator
D)series regulator

Question 8

Refer to the figure above. The purpose for the diode D1 is to

A)sense the error signal.
B)amplify the error signal.
C)supply a reference voltage.
D)limit the input voltage to the circuit.

Question 9

In a step- up regulator, the output voltage is filtered with a

A)diode.
B)choke- input filter.
C)capacitor- input filter.
D)voltage divider.

Question 10

The main difference between the 78XX and 79XX series regulators is that

A)the 78XX series is fixed and the 79XX series is adjustable.
B)the 78XX series is adjustable and the 79XX series is fixed.
C)the 78XX series provides a negative fixed output voltage and the 79XX series provides a positive fixed output voltage.
D)the 78XX series provides a positive fixed output voltage and the 79XX series provides a negative fixed output voltage.

Question 11

If the output of a voltage regulator varies from 15 to 14.7 V between the minimum and maximum load current, the load regulation is

A)0.
B)2%.
C)1%.
D)5%.

Question 12

The LM317 regulator provides an)

A)adjustable negative output voltage.
B)fixed negative output voltage.
C)fixed positive output voltage.
D)adjustable positive output voltage.

Question 13

Refer to the figure above. If the zener had a voltage rating of 3.7 V, Vout would be

A)20.2 V.
B)25 V.
C)18.2 V.
D)7.1 V.

Question 14

A voltage regulator with a no- load dc output of 15 V is connected to a load with a resistance of 12 ▲. If the load voltage decreases to 14.5 V, the percent regulation would be

A)96.7%.
B)100%.
C)3.45%.
D)3.33%.

Question 15

Simple current limiting may produce too much heat in the

A)ambient air.
B)pass transistor.
C)zener diode.
D)load resistor.

Question 16

The 78XX series of voltage regulators produces an output voltage that is

A)positive.
B)either positive or negative.
C)negative.
D)unregulated.

Question 17

Without current limiting, a shorted load will probably

A)destroy diodes and transistors.
B)have a load voltage equal to the zener voltage.
C)have too little load current.
D)produce zero load current.

Question 18

To get more output voltage from a step- down switching regulator, you have to

A)increase the switching frequency.
B)increase the duty cycle.
C)decrease the input voltage.
D)decrease the duty cycle.

Question 19

If the load is shorted, the pass transistor has the least power dissipation when the regulator has

A)foldback limiting.
B)a high zener voltage.
C)buck topology.
D)low efficiency.

Question 20

An increase of line voltage into a power supply usually produces

A)a decrease in efficiency.
B)a decrease in load resistance.
C)an increase in load voltage.
D)less power dissipation in the rectifier diodes.

Question 21

Refer to the figure above. To increase the current handling capability of this regulator, beyond the 5 A rating of the transistor, the reasonable thing to do would be to

A)increase the value of the zener diode.
B)change the values of R2 and R3.
C)place another transistor in series with Q1.
D)place another transistor in parallel with Q1.

Question 22

A series regulator is an example of a

A)ac- to- dc converter.
B)switching regulator.
C)shunt regulator.
D)linear regulator.

Question 23

Refer to the figure above. The purpose for the op- amp is to

A)supply a reference voltage.
B)limit the input voltage to the circuit.
C)amplify the error signal.
D)sense the error signal.

Question 24

An advantage of shunt regulation is

A)little wasted power.
B)built- in short- circuit protection.
C)high efficiency.
D)low power dissipation in the pass transistor.

Question 25

Refer to the figure above. If a solder splash shorted the ends of R1 to each other, the result would be that

A)Q1 would open.
B)the output voltage would not change.
C)the op- amp would fail.
D)the zener would fail.

Question 26

Refer to the figure above. An increase in VOUT will cause Q1 to

A)conduct less.
B)open.
C)conduct the same.
D)conduct more.

Question 27

An advantage of a switching regulator is

A)the circuit is very efficient.
B)less heat and wasted power.
C)voltages can be stepped- up or stepped- down.
D)All of the above.
E)None of the above.

Question 28

If the output of a voltage regulator varies from 20 to 19.8 V when the line voltage varies over its specified range, the load regulation is

A)2%.
B)5%.
C)0.
D)1%.

Question 29

Switching regulator configurations include

A)step- up.
B)inverting.
C)step- down.
D)All of the above.

Question 30

With foldback current limiting, the load voltage approaches zero, and the load current approaches

A)the zener current.
B)a destructive level.
C)infinity.
D)a small value.

Question 31

A voltage regulator has a no- load output of 18 V and a full load output of 17.3 V. The percent load regulation is

A)1.04%.
B)96.1%.
C)4.05%.
D)0.25%.