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Subelement D

Display & Control Systems

Section 37

Display System Power Supplies

The display power supply provides the following:

  • +18 volts DC for the pulse forming network.
  • Correct Answer
    5 volts DC for logic circuits and ± 12 volts DC for analog and sweep circuits.
  • 80 volts AC for the antenna resolver circuits.
  • All of the above

Most digital equipment runs on 5V and 12V so Answer B. is the right one, especially since it mentions raster "sweep" ciruits.

Answer A. and C. are wrong because neither the pulse-forming network nor the antenna resolver are part of the display.

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The display power supply provides the following:

  • 5 volts DC for logic circuits.
  • ± 12 volts DC for analog and sweep circuits.
  • 17kV DC for the CRT HV anode.
  • Correct Answer
    All of the above

The display power supply provides the following:

All of the above

The display power supply in a radar system is responsible for providing power to various components of the display unit. These components may include logic circuits, analog circuits, sweep circuits, and the CRT (Cathode-Ray Tube) high-voltage anode.

"5 volts DC for logic circuits": Logic circuits in the display unit typically require a low voltage supply, commonly around 5 volts DC, to power digital components such as microprocessors, memory, and other digital logic devices.

"± 12 volts DC for analog and sweep circuits": Analog and sweep circuits often require dual power supplies, usually around ±12 volts DC, to power operational amplifiers, analog signal conditioning circuits, and sweep generators.

"17kV DC for the CRT HV anode": The CRT in a radar display requires a high-voltage supply to accelerate electrons and create the visual display on the screen. The high-voltage anode voltage can be as high as 17,000 volts DC to accelerate the electrons sufficiently to produce a bright and clear display.

The display power supply is designed to provide these various voltage levels to different components, ensuring proper operation of the display unit in a radar system. Therefore, the correct answer is "All of the above" because the display power supply provides the required voltages for logic circuits, analog and sweep circuits, and the CRT high-voltage anode.

Note: The question fails to state the display is an analog CRT - Cathode Ray Tube requiring High Voltage, in which case both A. and B. would be the right answers, and C. and D. would be wrong.

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In a display system power supply what is the purpose of the chopper?

  • Correct Answer
    It acts as an electronic switch between the raw DC output and the inverter.
  • It interrupts the AC supply line at a varying rate depending on the load demands.
  • It regulates the 5 volt DC output.
  • It pre-regulates the AC input.

The "Chopper", a.k.a. "Vibrator", is a mechanically-oscillating switch similar to an electronic inverter to transform DC into the AC to power a transformer in a power supply, so Anser A. is the right one.

Anser B. is wrong because the chopper's frequency is constant.

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In a display system power supply, what is the purpose of the inverter?

  • Inverts the polarity of the DC voltage applied to the voltage regulators.
  • Provides the dual polarity 12 volt DC supply.
  • Acts as the voltage regulator for the 5 volt DC supply.
  • Correct Answer
    Produces the pulsed DC input voltage to the power transformer.

The "Vibrator", a.k.a. "Chopper", is a mechanically-oscillating switch similar to an electronic inverter to transform DC into the AC to power a transformer in a power supply, so Answer D. is the right one.

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What would be a common switching frequency for a display system power supply?

  • Correct Answer
    18 kHz
  • 120 Hz
  • 60 kHz
  • 120 kHz

Modern power supplies are of the "switching" kinf due to their higher efficiency, lower cost and lighter weight.

Switching power supplies usually operate at frequencies of around 20 KHz, therefore Answer A. is the right one.

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What display system power supply output would use a tripler circuit?

  • The logic circuit supply.
  • The sweep circuit supply.
  • Correct Answer
    The HV supply for the CRT anode.
  • The resolver drive

"(Voltage) Tripler Circuits" are used to triple the voltage, i.e. when high voltage is required. Depending on screen size, old analog CRT - Cathode Ray Tube displays require voltages going from 15KV yo 50KV so thye tend to use Voltage Tripler Circuits and Answer C. is the right one.

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