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FACSIMILE SYSTEM
6.1.1 Protective circuit
The power supply circuit is provided with a protection function for over-
current and overvoltage on the primary side.
As protection against overcurrent, the power supply circuit is provided
with a current fuse. When an overcurrent flows, this fuse blows due to self-
heating, preventing overcurrent from flowing to the circuit from then on.
As protection against overvoltage, the power supply circuit is provided
with a varistor. When a voltage exceeding the rated voltage of the varistor
is applied to the power supply line, the varistor causes a current to flow to
prevent voltage of and above the rated voltage from being applied.
A phototransistor and photocoupler are also provided extending across the
primary and secondary sides for detecting abnormal output voltage. When
the photocoupler on the secondary side detects an abnormal output volt-
age, it relays this to the phototransistor on the primary side, and stops
oscillation to stop supply of the power voltage.
6–26
Power supply outlet
Fig. 6-26 Protective Circuit
Current fuse
Current
FG
Varistor
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