IBM
Personal Computer XT Power
Supply
Description
The
system dc
power
supply is a 130-watt, 4 voltage-level
switching regulator.
It
is integrated into
the
system unit
and
supplies
power
for
the
system unit, its options,
and
the keyboard.
The
supply provides 15 A
of
+5
Vdc, plus
or
minus
5%,
4.2 A
of
+ 12 Vdc, plus
or
minus
5%,
300
mA
of
-5 Vdc, plus
or
minus
10%,
and
250
mA
of
-12
Vdc, plus
or
minus
10%.
All power
levels are regulated with overvoltage
and
overcurrent protection.
There
are two
power
supplies,
120
Vac
and
220/240
Vac.
Both
are
fused. If
dc
overcurrent
or
overvoltage conditions exist, the
supply automatically shuts
down
until the condition
is
corrected.
The
supply is designed for continuous operation
at
130 watts.
The
system
board
takes approximately 2
to
4 A
of
+ 5 Vdc, thus
allowing approximately
11
A
of
+5
Vdc for
the
adapters in the
system expansion slots.
The
+ 12 Vdc
power
level is designed to
power
the
internal diskette drives
and
the
10M
or
20M
fixed disk
drive.
Th.e
-5
Vdc
level is used for analog circuits in
the
diskette
adapter's
phase-lock loop.
The
+ 12 Vdc
and
-12
Vdc
are used
for
powering
the
Electronic Industries Association
(EIA)
drivers
for
the
communications adapters. All four
power
levels are
bussed
across the eight system expansion slots.
The
IBM
Monochrome
Display has its
own
power
supply,
receiving its ac
power
from
the
system unit's
power
system. The
ac
output
for
the
display is switched
on
and
off
with
the
Power
switch
and
is
a
nonstandard
connector.
Power Supplies 3-3
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