Input Section
Ac line voltage is supplied
to
the
input
section
through
the
power cord. Functions
of
the
input
section are:
• High Frequency Filtering.
• Fusing.
• On-Off Switching.
•
Input
Voltage Selection.
• Low Frequency Filtering.
t'Ugh
Frequency Filtering
Line
input
voltage
through
the
power cord is applied
to
a high-frequency line filter.
This
filter
traps
high frequency noise from
both
entering
or
leaving
the
power supply.
It
enables
the
output
voltages
to
be
virtually free from voltage spikes
that
may
appear
at
the
input.
The
filtered
output
is sent
to
the
fuse
and
power switch.
Fuse
For
both
line voltage ranges,
the
same
size fuse
protects
the
power supply. Voltage selection
and
fuse size
are
shown in Table 3-1.
Table 3-1. Voltage Ranges and Fusing
Voltage Setting Tolerance Fuse Rating
120 Vac
+10%,
-25%
8AF
250
Volt
240
Vac
+4%,
-19%
8AF
250
Volt
The
fuse
rating
8AF
means
an
8 arnpere fuse
with
a
type
F delay before blowing. In
both
cases,
the
line frequency is 48-66 Hz.
Low Frequency Filtering
'Nhen
the
power switch is
turned
on, voltage is applied
to
the
Low Frequency Filtering circuits.
These
circuits
trap
low frequencies entering
or
leaving
the
power supply.
They
also reduce ripple
in
the
output
voltages
..
After filtering,
the
line voltage
is
sent
to
the
Bridge Rectifier Section.
()n-Off Switching
This
operator-controlled switch connects power
to
the
Low Frequency Line Filter.
Located
on
the
computer
(or
expander)
front panel,
it
is
mechanically connected
to
the
power supply by a
switch extension.
When
turned
to
the
ON
position, a green LED
on
the
front panel is lit.
The
LED
is
connected
to
the
voltage
outputs
and
indicates
that
all power supplies
are
operating.
Input Voltage Selection
A voltage select switch is set
to
either
the
120 Vac
or
240 Vac position,
depending
on
the
line
voltage. Voltage selection changes
the
input
voltage
to
the
bridge rectifier
to
make
the
bridge
output
the
same
for
either
line voltage.
Functional Description
67
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