Protection
and
Reset
Circuits
Functions
of
the
Protection
and
Reset Circuits are:
• Overvoltage
Protection
• Reset Signal Generation
Overvoltage
Protection
Circuit
All
output
voltages are
inputs
to
the
Overvoltage
Protection
Circuit.
If
the
voltage goes high,
the
circuit will
shut
down
the
power supply, protecting its components as well as cOInponents
in
other
areas
of
the
computer
(or bus expander).
The
output
of
the
Overvoltage
Protection
Circuit feeds
the
Switching Control Circuit.
Reset
Circuit
When
ac line voltage is applied,
the
power supplies
start
building
up
their
output
voltages.
The
+5
and
+
12
V dc supplies
input
the
Reset Circuit. As these
inputs
reach
their
operating
voltages,
the
processor
board
circuits are also being powered up.
When
normal
operating
levels
are reached, a Power-
U
pRESET
(PURESET)
signal
is
sent
to
the
CPU
to
initialize
it
and
start
the
Boot
ROM
sequence.
Power
Distribution
Power Distribution
routes
power
to
the
functional assemblies installed
• Overvol
tage
Protection
• Reset Signal Generation
Figure 3-2 shows how power
is
distributed
in
the
computer. Figure 3-3 shows how power
is
distributed
in
the
bus expander.
Ac
"
+5J~
+ 1" 012V
POWER
SUPPLY
I
Pooc=oR
I
BOAAD
I
_@
fRONT
PANE
LED
L
I
.....
HICS
I
BOAAD
I
Te.t Point.
I
LARGE
FAN
J
V
-
-
MOTHERBOARD
I
SMALL
FAN
I
I/O
BACKPLANE
Figure 3-2. Computer Power Distribution
Functional Description
41
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