Rectification and Switching Control Circuits
Functions
of
the
Rectification
and
Switching Control circuits are:
• Full-Wave Bridge Rectifier.
• Switching Control Circuit.
• Power Transformer.
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.
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
Vdc Power Supply.
•
+12
Vdc Power Supply.
•
-12
V dc Power Supply.
+5
Vdc
Voltage from
the
power
transformer
feeds
through
a
+5
V dc
current
sensor
than
goes
to
the
+5
V dc rectifier.
Output
from
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 Vdc
Voltage from
the
power
transformer
feeds
through
a rectifier
then
to
a
+12
Vdc
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
expander),
the
+12
Vdc
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.
68
Functional Description
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