Theory
of
Operation
2-7
-
2V.
The +
6V,
+ 3V,
and
-
2V
outputs are used exclusively by the processor stack. Also, a
separate
+ 12V output
is
produced to drive mass storage devices.
A temperature-sensing thermistor
is
mounted on the secondary board heat sink. This thermistor
is
monitored by the supervisor board
and
controls the power supply fan and the processor stack fan.
These two dc box fans operate at three speeds:
low,
medium, and high.
When the power supply assembly thermistor detects that the temperature of the secondary board
heat sink has risen above
39°C, the circuitry steps the fans to medium speed. A further rise of
temperature above
51°C causes stepping of the fans to high speed,
and
the user
is
notified that the
fans have reached their maximum speed.
At
97°C, a power
fail
warning (NPFW)
is
transmitted,
and
4 to 8 ms later the power supply
is
shut down. The power supply assembly
is
also shut down
if
a
temperature sensor
on
the CPU finstrate
in
the processor stack detects a temperature over 100°C.
When cooling
off,
the fans step from high to medium speed when the temperature drops below
46°C,
and
from medium to low speed when the temperature drops below 34°C.
Supervisor Board
The supervisor board contains most of the monitoring, control,
and
fault-indicating circuitry for the
power supply assembly.
The overvoltage and undervoltage monitor checks the voltage outputs of
all
secondary board
power supplies except the
+ 12MMV supply for mass storage devices. The monitor also checks the
+ 5 V output
and
the peak power monitor from the primary board. If a fault
is
detected, the pulse
width modulator
is
disabled, the shutdown sequence
is
enabled,
and
the appropriate LEDs are
lit.
Temperature monitors check the power supply assembly thermistor, described
in
preceding para-
graphs,
and
the processor stack thermistor. When the processor stack temperature exceeds 100°C
or the power supply temperature exceeds 97°C, this board generates the power
fail
warning
(NPFW) signal
and
initiates the shutdown sequence.
A
+ 10V reference supply provides the voltage condition references for over
and
under voltage
monitoring
and
temperature sensing. This supply
is
enabled by the + 16V bias supply from the
primary board.
The fan control circuitry provides a constant
-10V
to the
110
card cage fan (FANIon Figure 2-3)
whenever power
is
on. This fan never changes speed. The fan control circuitry also provides - 10V
to the power supply assembly fan (FANP)
and
processor stack fan
(FANF)
as long as the power
supply
assembly temperature does not exceed 39°C. When the power supply assembly thermistor
detects between
39°C
and
51°C, the fan control circuitry provides - 12V to the two fans, stepping
them to medium speed. Between
51°C
and
97°C, the fans are stepped to high speed at
-14V.
The
fan high signal (NFANHI)
is
also sent to the processor which sends a message to the user, indicating
that the computer
is
performing maximum cooling and that a further temperature increase could
result
in
shutdown.
If either the
110
door or processor stack door
is
opened while the power supply assembly
is
operating, the shutdown sequence
is
initiated.
To Next Page
Loading...
Need help?
General
