Switching
Control
Circuit
Voltage from
the
rectifier feeds a Switching Control Circuit
that
controls
the
amount
of
power
going
to
each of
the
output
voltage regulators.
+5
V dc feedback is applied
to
the
Switching
Control Circuit
to
regulate
the
+5
V dc
output.
Overvoltage protection signals also
input
the
Switching Control Circuit
that
will cause
the
power supply
to
shut
down if voltage in
the
output
supplies goes
too
high. A
+5
V dc over-current sensor
input
is
another
input
to
the
Switching
Control Circuit.
Power
Transformer
Input
ac voltage
is
also applied
to
the
primary
windings of a power transformer.
Three
sets
of secondary windings each feed a voltage regulator for
the
output
voltages. A voltage select
switch
is
set
to
the
line voltage range
and
causes
the
power transformer
to
have
the
same voltage
output
for
both
line voltage ranges.
Power
Supply
Regulators
Functions of
the
Power Supply Regulators are:
•
+5
V dc Power Supply
• +
12
V dc Power Supply
•
-12
V dc Power Supply
+5
V
de
Voltage fronl
the
power
transformer
feeds
through
a
+5
V dc
current
sensor
than
goes
to
the
+5
V dc rectifier.
Output
frOln
the
+5
V dc rectifier is nominally 5.07 V dc
±0.18
V dc.
The
+5
V dc
output
is
also fed
to
the
+5
V dc Feedback Loop Circuit for regulation.
It
also is fed
to
the
Overvoltage
Protection
Circuit
and
Reset Circuit.
If
the
+5
V dc fails,
the
Power-On LED
on
the
front panel will go
out
as
the
+5
V dc
is
part
of
the
controlling voltage for
the
Switching
Control Circuit.
+12
V
de
Voltage frolll
the
power
transformer
feeds
through
a rectifier
then
to
a +
12
V dc
Post
Regulator.
The
output
from
the
Post
Regulator is nominally + 12.29
V'dc
±0.43 V dc. In
addition
to
being
distributed
in
the
computer
(or bus expander),
the
+12
V dc
output
is
also fed
to
the
Overvoltage
Protection
Circuit
and
Reset Circuit.
External
to
the
power supply,
the
+
12
V dc
is
connected
to
one side of
the
Power-On LED on
the
front panel.
-12
V
de
Voltage
frOIn
the
power
transformer
feeds directly
to
a
-12
V dc
Post
Regulator.
The
output
from
the
Post
Regulator
is
nOIninally
-12.29
V dc ±0.43 V dc. In addition
to
being
distributed
in
the
computer
(or bus expander),
the
+12
V dc
output
is
also fed
to
the
Overvoltage
Protection
Circuit
and
Reset Circuit.
External
to
the
power supply,
the
-12
V dc
is
connected
to
the
other
side of
the
Power-On LED on
the
front panel.
40
Functional Description
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