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FACSIMILE SYSTEM
6. POWER SUPPLY UNIT
The "power supply unit (regulator)" converts the alternating current (AC)
for household use into a direct current (DC) constant voltage power
source. A "constant voltage power source" refers to a power source whose
output is maintained at a fixed output voltage even if the input voltage or
output current fluctuate.
Series regulators and switching regulators are generally used as a DC con-
stant voltage power supply. Facsimiles mainly use switching regulators.
The reason why a switching regular has been selected is that even though
its circuit is more complicated than that of a series regulator, it is ideal for
downsizing and allows the power supply unit itself to be made compact.
Another reason why a switching regulator has been selected is that it dem-
onstrates good stable power supply efficiency and generates little heat.
The following describes what sort of power supply a switching regulator is
as switching regulators are used on almost all facsimiles.
6.1
Switching Regulator
Switching regulators supply only voltage that has dropped due to the load,
and turn semiconductor switches ON and OFF ("switching") to control the
supply voltage for maintaining a constant voltage. This is why this kind of
regulator is called a "switching regulator."
Switching regulators compare fluctuations in the output voltage with the
reference voltage, and change the time ratio (duty ratio) of the ON and
OFF states of the input DC voltage switch according to the result of this
comparison to control the output voltage to a constant voltage.
6–24
Table 6-1 Features of Switching Regulators and Series Regulators
Power Supply Type
Switching regulator
Series regulator
Features
• Compact size and light weight
• High efficiency
• Complicated circuit
• Large noise
• Large size and heavy weight
• Low efficiency
• Simple circuit
• Small noise
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