HP 3000 III Series Manual page 346

HP 32421A Series III Power Supplies
width of the cabinet and has a 4 by 2-5/8 inch opening used for
accessing power supply controls. When an HP 30312A Power Supply
is mounted next to this power supply, a half panel covers only
the HP 30311A Power Supply. The power supply provides +12.7V,
+12.0V, +5.0V, -3.0V, and -5.0V for the semiconductor memory.
The Semiconductor Memory Array PCA uses all the dc vol tages ex-
cept -3.0V. The Semiconductor Memory Control PCA uses only the
+5.0V output.
The power supply normally operates from the +20V, -20V, and +15V
outputs of the HP 30310A Power Supply as shown in figure 9~3.
When ac input power to the HP 30310A Power Supply is interrupted,
a 7-cell, lead-acid battery pack in the HP 30311A Power Supply
furnishes the input power and maintains the voltages to the mem~
ory. The amount of time the battery continues to furnish power
depends on the condition of the battery and the size of memory
requiring power. Normally, the battery will furnish power for 40
to 90 minutes before it discharges to a level that activates the
undervoltage circuits and removes all power from memory. The
power supply can be operated without the battery. However, no
power will be available to the memory system if ac power is re-
moved from the
HP
30310A Power Supply. When operating in this
mode, the battery status lights are disabled. A battery mode
sw itch on the 30311-60003 Control PCA must be set to operate
without a battery.
The +20-volt output of the HP 30310A Power Supply provides the
charging power for the battery pack and the input power for the
+12.7V, +12.0V, and +5.0V regulators. (see figure 9-3.) The TEMP
SENSE input to the HP 30310A controls the output of the +20V
line. The +20V output also supplies input power to the +5V regu-
lator and the control circuits.
Outputs of -3V and -5V are derived from a source voltage obtained
fr em the +5V sw itching regulator. Load cur rent fr om the -3V line
adds to the -5V load current so that a single current limit on
the -5V line protects both outputs. The maximum comb ined current
for the -3V and -5V loads may be divided between the loads in any
combination.
Over/under voltage detectors can disable the PSU (Power Supply
tp)
system dc power line, and shut down the power supply by sens-
ing the +12.0V, +5V, and -5V outputs for undervoltage. The -3V
output is sensed for undervoltage to disable the +12.0V and
+12.7V outputs, thus protecting the memory array chips from lack
of either -3V or -5V substrate bias. Overvoltage conditions
sensed on the +5V and +12. OV outputs cause the power supply to
c-rowbar to protect the TTL elements and memory array chips.
Controls and indicators mounted on the front panel of the HP
30311A Power Supply and on the DC Control Panel are provided to
monitor and control power supply status and operation. In addi-
tion, test points on the power supply front panel are provided as
an aid in troubleshooting. An internal three-position slide-
switch permits power supply operation with a battery or without a
9-12