Protection And Reset Circuits; Power Distribution - HP 9000 Series 310 Service Information Manual

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