New Zealand NZART pool, section ZLF21

Subelement ZLF

Power Supplies

Section ZLF21

Power Supplies

ZLF2101

A mains operated DC power supply

A.
converts DC from the mains into AC of the same voltage
Correct Answer
B.
converts energy from the mains into DC for operating electronic equipment
C.
is a diode-capacitor device for measuring mains power
D.
is a diode-choked device for measuring inductance power

ZLF2101

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ZLF2102

The following unit in a DC power supply performs a rectifying operation

A.
an electrolytic capacitor
B.
a fuse
C.
a crowbar
Correct Answer
D.
a full-wave diode bridge

ZLF2102

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ZLF2103

The following unit in a DC power supply performs a smoothing operation

Correct Answer
A.
an electrolytic capacitor
B.
a fuse
C.
a crowbar
D.
a full-wave diode bridge

ZLF2103

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ZLF2104

The following could power a solid-state 10 watt VHF transceiver

Correct Answer
A.
a 12 volt car battery
B.
6 penlite cells in series
C.
a 12 volt, 500 mA plug-pack
D.
a 6 volt 10 Amp-hour Gel cell.

ZLF2104

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ZLF2105

A fullwave DC power supply operates from the New Zealand AC mains. The ripple frequency is

A.
25 Hz
B.
50 Hz
C.
70 Hz
Correct Answer
D.
100 Hz

ZLF2105

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ZLF2106

The capacitor value best suited for smoothing the output of a 12 volt 1 amp DC power supply is

A.
100 pF
B.
10 nF
C.
100 nF
Correct Answer
D.
10,000 uF

ZLF2106

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ZLF2107

The following should always be included as a standard protection device in any power supply

A.
a saturating transformer
Correct Answer
B.
a fuse in the mains lead
C.
a zener diode bridge limiter
D.
a fuse in the filter capacitor negative lead

ZLF2107

There should always be a fuse in the phase or active AC mains lead for protection if a fault develops in the equipment. The fuse should be of the correct rating for the task. Keep some spare fuses handy!

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ZLF2108

A halfwave DC power supply operates from the New Zealand AC mains. The ripple frequency will be

A.
25 Hz
Correct Answer
B.
50 Hz
C.
70 Hz
D.
100 Hz

ZLF2108

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ZLF2109

The output voltage of a DC power supply decreases when current is drawn from it because

A.
drawing output current causes the input mains voltage to decrease
B.
drawing output current causes the input mains frequency to decrease
Correct Answer
C.
all power supplies have some internal resistance
D.
some power is reflected back into the mains.

ZLF2109

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ZLF2110

Electrolytic capacitors are used in power supplies because

A.
they are tuned to operate at 50 Hz
B.
they have very low losses compared to other types
C.
they radiate less RF noise than other types
Correct Answer
D.
they can be obtained in larger values than other types

ZLF2110

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