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Subel. B
6 questions
Subelement B

Transmitting Systems

Section 18

Power Supplies

An advantage of resonant charging is that it:

  • Eliminates the need for a reverse current diode.
  • Guarantees perfectly square output pulses.
  • Correct Answer
    Reduces the high-voltage power supply requirements.
  • Maintains a constant magnetron output frequency.
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The characteristics of a field-effect transistor (FET) used in a modern RADAR switching power supply can be compared as follows:

  • "On" state compares to a bipolar transistor. "Off" state compares to a 1-Megohm resistor.
  • Correct Answer
    "On" state compares to a pure resistor. "Off" state compares to a mechanical relay.
  • "On" state compares to an low resistance inductor. "Off" state compares to a 10-Megohm resistor.
  • "On" state compares to a resistor. "Off" state compares to a capacitor.

A circuit to switch something On and Off you can utilize a Relay. KD9TIP

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

  • Provide the reference voltage for the regulator.
  • Vary the frequency of the switching regulator to control the output voltage.
  • Correct Answer
    Vary the duty cycle of the regulator switch to control the output voltage.
  • Compare the reference voltage with the output voltage sample and produce an error voltage.
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In a fixed-frequency switching power supply, the pulse width of the switching circuit will increase when:

  • Correct Answer
    The load impedance decreases.
  • The load current decreases.
  • The output voltage increases.
  • The input voltage increases.
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A major consideration for the use of a switching regulator power supply over a linear regulator is:

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

A major consideration for the use of a switching regulator power supply over a linear regulator is that the overall efficiency of a switching regulator is much higher than a linear power supply.

When it comes to power conversion, efficiency is a critical factor. Efficiency refers to the ratio of output power to input power and indicates how effectively a power supply converts input energy into usable output energy.

Switching regulators employ a different mechanism compared to linear regulators for voltage regulation. They utilize high-frequency switching to rapidly control the flow of energy and adjust the output voltage. This switching action allows for more efficient power conversion as it minimizes energy loss.

In contrast, linear regulators regulate the output voltage by dissipating excess energy as heat. This method results in significant energy loss and lower efficiency, especially when the input-output voltage difference is large.

The higher efficiency of switching regulators translates to less energy waste and reduced heat generation, making them more desirable for applications where energy efficiency and heat management are crucial.

Mnemonic: "Efficiency Advantage"

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Which of the following characteristics are true of a power MOSFET used in a RADAR switching supply?

  • Low input impedance; failure mode can be gate punch-through.
  • Correct Answer
    High input impedance; failure mode can be gate punch-through.
  • High input impedance; failure mode can be thermal runaway.
  • Low input impedance; failure mode can be gate breakdown.
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