Key Topic 18: Power Supplies

Question 1

8-18B1: An advantage of resonant charging is that it:

A. Eliminates the need for a reverse current diode.
B. Guarantees perfectly square output pulses.
C. Reduces the high-voltage power supply requirements.
D. Maintains a constant magnetron output frequency.

Answer 1

C. Reduces the high-voltage power supply requirements.

Question 2

8-18B2: The characteristics of a field-effect transistor (FET) used in a modern RADAR switching power supply can be compared as follows:

A. “On” state compares to a bipolar transistor. “Off” state compares to a 1-Megohm resistor.
B. “On” state compares to a pure resistor. “Off” state compares to a mechanical relay.
C. “On” state compares to a low resistance inductor. “Off” state compares to a 10-Megohm resistor.
D. “On” state compares to a resistor. “Off” state compares to a capacitor.

Answer 2

B. “On” state compares to a pure resistor. “Off” state compares to a mechanical relay.

Question 3

8-18B3: A pulse-width modulator in a switching power supply is used to:

A. Provide the reference voltage for the regulator.
B. Vary the frequency of the switching regulator to control the output voltage.
C. Vary the duty cycle of the regulator switch to control the output voltage.
D. Compare the reference voltage with the output voltage sample and produce an error voltage.

Answer 3

C. Vary the duty cycle of the regulator switch to control the output voltage.

Question 4

8-18B4: In a fixed-frequency switching power supply, the pulse width of the switching circuit will increase when:

A. The load impedance decreases.
B. The load current decreases.
C. The output voltage increases.
D. The input voltage increases.

Answer 4

A. The load impedance decreases.

Question 5

8-18B5: A major consideration for the use of a switching regulator power supply over a linear regulator is:

A. The switching regulator has better regulation.
B. The linear regulator does not require a transformer to step down AC line voltages to a usable level.
C. The switching regulator can be used in nearly all applications requiring regulated voltage.
D. The overall efficiency of a switching regulator is much higher than a linear power supply.

Answer 5

D. The overall efficiency of a switching regulator is much higher than a linear power supply.

Question 6

8-18B6: Which of the following characteristics are true of a power MOSFET used in a RADAR switching supply?

A. Low input impedance; failure mode can be gate punch-through.
B. High input impedance; failure mode can be gate punch-through.
C. High input impedance; failure mode can be thermal runaway.
D. Low input impedance; failure mode can be gate breakdown.

Answer 6

B. High input impedance; failure mode can be gate punch-through.