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Subelement ZLF
Power Supplies
Section ZLF22
Regulated Power Supplies
The block marked 'Filter' in the diagram is to
  • filter RF radiation from the output of the power supply
  • Correct Answer
    smooth the rectified waveform from the rectifier
  • act as a 50 Hz tuned circuit
  • restore voltage variations
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The block marked 'Regulator' in the diagram is to
  • regulate the incoming mains voltage to a constant value
  • ensure that the output voltage never exceeds a dangerous value
  • keep the incoming frequency constant at 50 Hz
  • Correct Answer
    keep the output voltage at a constant value
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The block marked 'Transformer' in the diagram is to
  • transform the incoming mains AC voltage to a DC voltage
  • ensure that any RF radiation cannot get into the power supply
  • Correct Answer
    transform the mains AC voltage to a more convenient AC voltage
  • transform the mains AC waveform into a higher frequency waveform
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The block marked 'Rectifier' in the diagram is to
  • Correct Answer
    turn the AC voltage from the transformer into a fluctuating DC voltage
  • rectify any waveform errors introduced by the transformer
  • turn the sinewave output of the rectifier into a square wave
  • smooth the DC waveform
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The block marked 'Regulator' in the diagram could consist of
  • four silicon power diodes in a regulator configuration
  • two silicon power diodes and a centre-tapped transformer
  • Correct Answer
    a three-terminal regulator chip
  • a single silicon power diode connected as a half-wave rectifier
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In the block marked regulator in the diagram below, a reversed diode may be present across the regulator. Its job is to
  • Block negative voltages from appearing at the output
  • Blow a fuse if high voltages occur at the output
  • Blow a fuse if negative currents occur at the output
  • Correct Answer
    Bypass the regulator for higher voltage at its output compared to its input
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A power supply is to power a solid-state transceiver. A suitable over-voltage protection device is a
  • Correct Answer
    crowbar across the regulator output
  • 100 uF capacitor across the transformer output
  • fuse in parallel with the regulator output
  • zener diode in series with the regulator
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In a regulated power supply, the 'crowbar' is a
  • means to lever up the output voltage
  • circuit for testing mains fuses
  • Correct Answer
    last-ditch protection against failure of the regulator in the supply
  • convenient means to move such a heavy supply unit
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In a regulated power supply, 'current limiting' is sometimes used to
  • prevent transformer core saturation
  • protect the mains fuse
  • Correct Answer
    minimise short-circuit current passing through the regulator
  • eliminate earth-leakage effects
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The purpose of a series pass transistor in a regulated power supply is to
  • suppress voltage spikes across the transformer secondary winding
  • work as a surge multiplier to speed up regulation
  • amplify output voltage errors to assist regulation
  • Correct Answer
    allow for a higher current to be supplied than the regulator would otherwise allow
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