Deck 17: Voltage Regulators

Question 1

Figure 1
Refer to Figure 1. Current limiting is at an output current of

A)3.5 A
B)1.0 A
C)0.5 A
D)2.0 A

Answer 1

B

Question 2

Figure 3 Assume ideal components.
Refer to Figure 3. The purpose of diode D1 is to

A)prevent overshoots from affecting the output
B)prevent negative pulses from affecting the output when Q1 is ON
C)prevent the capacitor from discharging through the transistor
D)provide a current path for load current when Q1 is OFF

Answer 2

D

Question 3

Foldback current limiting differs from normal current limiting in that excessive output current will

A)shut off the power supply
B)maintain the maximum allowed current but not exceed it
C)be shunted to ground by the current limiting circuit
D)reduce the output current limit

Answer 3

D

Question 4

Figure 2
Refer to Figure 2. Assume the input increases by 0.45 V. As a result, the current in Q1 will increase by about

A)1.0 mA
B)1.5 mA
C)0.5 mA
D)2.0 mA

Question 5

Figure 2
Refer to Figure 2. If the load voltage drops, the voltage across R4 will and the collector current of Q1 will .

A)decrease, increase
B)decrease, decrease
C)increase, decrease
D)increase, increase

Question 6

Figure 2
Refer to Figure 2. The current in the zener is approximately

A)7.5 mA
B)19 mA
C)26 mA
D)16 mA

Question 7

Figure 4
Refer to Figure 4. The capacitor is supplying current to the load

A)at all times
B)when the inductor field is collapsing
C)when the transistor is on
D)none of the above

Question 8

Figure 4
Refer to Figure 4. The type of regulator is a

A)inverting switching regulator
B)step- up switching regulator
C)step- down switching regulator
D)linear shunt regulator

Question 9

The ADP1612/ADP1613 IC switching regulator has 2 selectable switching frequencies. The higher frequency is selected for

A)greater output voltage range
B)higher efficiency
C)smaller external components
D)all of the above

Question 10

Shunt regulators are

A)electrically noisy
B)simple
C)efficient
D)all of the above

Question 11

Figure 4
Refer to Figure 4. When the transistor is ON, the

A)inductor field is collapsing and D1 is not conducting
B)inductor field is collapsing and D1 is conducting
C)inductor field is building and D1 is not conducting
D)inductor field is building and D1 is conducting

Question 12

A 12 V power supply has ROUT of 20 m▲ at a maximum current of 1.5 A. The load regulation is

A)0.25%
B)0.75%
C)0.5%
D)none of the above

Question 13

Figure 3 Assume ideal components.
Refer to Figure 3. Assume the regulator is 80% efficient when VIN =+18 V and VOUT = +12 V. The input current is approximately

A)320 mA
B)750 mA
C)2.0 A
D)500 mA

Question 14

Figure 2
Refer to Figure 2. The maximum input voltage is 18 V. The power rating of R1 for worst- case loading is

A)22 W
B)30 W
C)15 W
D)8.2 W

Question 15

Figure 3 Assume ideal components.
Refer to Figure 3. Assume VIN can vary between +15 V and +18 V. To obtain an output of +12 V, the duty cycle must vary between

A)80% and 90%
B)33% and 67%
C)67% and 80%
D)20% and 33%

Question 16

A regulator output changes from +12.1 V with no load to +11.9 V at the rated current of 2.0 A. The load regulation can be expressed as

A)1.12%/A
B)3.36%/A
C)1.68%/A
D)0.84%/A

Question 17

The current sensor for a current limiting circuit is a

A)series resistor
B)comparator
C)series transistor
D)zener diode

Question 18

Figure 1
Refer to Figure 1. The output voltage is approximately

A)8.3 V
B)6.8 V
C)10 V
D)12 V

Question 19

Figure 1
Refer to Figure 1. If R2 is replaced with a short (0 ▲), the output voltage will be

A)3.5 V
B)5.1 V
C)0 V
D)none of the above

Question 20

Figure 1
Refer to Figure 1. The voltage at the base of Q1 should be

A)11.3 V
B)9.3 V
C)12.7 V
D)none of the above

Question 21

An ideal power supply has a Thevenin resistance of zero ohms.

Question 22

Linear regulators do not require a pulse width modulator.

Question 23

A 7912 regulator has an output of +12 V.

Question 24

Switching regulators can step- up, step down, or invert the output.

Question 25

To regulate properly, the input voltage to a 7805 must be equal or greater than

A)10.0 V
B)6.5 V
C)5.5 V
D)7.5 V

Question 26

An LM 337 is

A)an adjustable negative output regulator
B)an adjustable positive output regulator
C)a fixed positive output regulator
D)a fixed negative output regulator

Question 27

Figure 5
Refer to Figure 5. The purpose of Qext and Rext is to

A)provide current limiting
B)convert the 78XX to a current source
C)both A and B
D)none of the above

Question 28

The VREF of a series regulator must be equal to VOUT.

Question 29

Figure 3 Assume ideal components.
Refer to Figure 3. A disadvantage of this type of regulator is that

A)the pass transistor tends to be very hot
B)it generates electromagnetic interference (EMI)
C)it has poor load regulation
D)all of the above

Question 30

Figure 6
Refer to Figure 6. Ignoring IADJ, the output voltage range is approximately

A)1.75 V to 15.6 V
B)1.00 V to 11.2 V
C)1.50 V to 13.4 V
D)1.25 V to 12.4 V

Question 31

High temperature can change the output of a regulated power supply.

Question 32

Figure 2
Refer to Figure 2. The output voltage is approximately

A)11 V
B)5.1 V
C)6.2 V
D)8.5 V

Question 33

Ideally, line regulation is 100%.

Question 34

A shunt regulator does not use negative feedback.

Question 35

Of the following types, the most efficient regulator is a(n)

A)shunt regulator
B)IC switching regulator
C)7805 IC regulator
D)series regulator