High
Frequency
Filtf~ring
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 below:
Voltage
Setting
120 V ac
240 V ac
Line Voltage Fuse
Rating
85
to
129 V ac
8A
Normal
Blow
187
to
255 V ac
8A
Normal
Blow
In
both
cases,
the
line frequency
is
48-66 Hz.
Low
Frequency
Filtering
When
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.
On-Off
Switching
This
operator-controlled switch connects power
to
the
Low
Frequency Line Filter. Located on
the
computer
(or bus 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 V ac
or
240 V ac 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.
Rectification
and
Switching
Control
Circuits
Functions
of
the
Rectification
and
Switching Control circuits are:
• Full-Wave Bridge Rectifier
• Switching Control Circuit
•
Power Transfornler
Full-Wave
Bridge
Rectifier
Part
of
the
input
ac voltage is applied across a full-wave bridge network
that
outputs
a DC
voltage. Large storage capacitors charge
up
to
this
voltage
and
provide a
constant
energy
supply
to
the
individual power supply circuits.
Functional Description
39
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