Data General NOVA 4/C Field Reference Manual page 65

Data General Corporation (DGC) has prepared this manual for use by DGC personnel and customers as a guide to the proper installation, operation, and
maintenance of DGC equipment and software. The drawings and specifications contained herein are the property of DGC and shall neither be reproduced in whole or
in part without DGC's prior written approval nor be implied to grant any license to make, use, or sell equipment manufactured in accordance herewith.
to the low state and disables the buck regulator for the
remainder of the 40 KHz clock cycle (the regulator
turns on again at the start of the next cycle). This
effectively reduces the duty cycle of the pulse width
modulator, and so limits the amount of power delivered.
(The supply actually goes into full current limiting
when you first turn it on in order to charge the output
filter capacitors). If the supply stays in current limiting
too long, the limiter circuits drive the RP8 signal to the
high state.
When an over-current fault occurs, the over-current light
turns on and the detector drives the PON and COMP signals
to the low state. This shuts down the entire supply. The
detector re-enables the supply two seconds later. If the
overload is still present, the detector shuts the supply down
again. This process can continue for five more cycles. If
the overload is still present, the supply shuts down for
The over-voltage detectors monitor the +15V, +12V and
level, the over-voltage light turns on and the detector
shuts down the supply. (The -5V regulator has a built-in
over-voltage protector. If a fault occurs, the protector
clamps the -5V bus to less than -8 volts.)
The memory disaster detector monitors the MEMD signal
loses -5 MEM, a critical memory voltage, the memory
disaster light comes on and the detector shuts down the
The under-voltage detector monitors all of the output
voltages. If any output falls below a preset level, the
detector drives the Power OK signal to the low state, turns
off the power-on light and flags a power failure. A power
failure is also flagged when the power switch is turned off
or if the 300 VNR supply fails.
Voltages Current
Output Min Max Min Max
Table 9.1 16-Slot chassis power supply specifications without battery
backup
*The sum of the currents on +12V, +15, and +12 MEM must NOT exceed
12.5 Amps.
Battery Backup
The battery backup option supports the memory voltages
when a power failure occurs. It also powers the system
clocks and the power status indicators and provides a
Memory OK status flag to indicate that the memory voltages
are okay. Figure 9.4 shows the parts of the battery backup
option that are added to the power supply board.
The battery backup option generates three voltages: +12
MEM, +5 MEM-P, and -5 MEM-P (note that the main supply
regulators support these voltages when battery backup is
not configured). It draws power from one of two sources.
During normal operation, power comes from the +12V
main supply output. If a failure occurs, power then comes
from the battery. The backup option includes three voltage
regulators along with some control circuits. To see how
these circuits work, let us examine each voltage regulator
and then follow a power failure sequence.
The + 12V regulator draws power directly from the battery.
It is a simple linear series pass design and has no built-in
The +5V regulator draws power from either the +12V main
supply or from the battery. It is a buck switching regulator
and is very similar to the one in the main supply. When
the low voltage switch turns on, current flows from the
source, through the primary winding of the flyback
transformer and on to the output. The pulse width
modulator controls the duty cycle of the switch to regulate
the output voltage. If too much current flows in the primary
winding, the current limiter reduces the modulator's duty
cycle.
The -5V regulator draws power from the +5V regulator via
the flyback transformer. It is a simple linear series pass
design and has built-in current limiting.
The battery on BATON controls battery backup operation.
When the supply operates normally, the PON is driven to
the high state and the BATON is driven to the low state.
This turns off the +12V regulator, and current flows from
the +12V supply, through the Schottky diode and to the
selects the +12V supply, which in turn powers the +5
MEM-P and -5 MEM-P outputs.
When a power failure occurs, the PON is driven to the low
state. If the failure did not occur because of a memory
disaster, the BATON is driven to the high state. This switches
the regulators over to battery operation. As long as the
battery retains sufficient charge, the + 12 MEM output stays
in regulation and the MEM OK is in the high state. But
when the battery discharges to a dangerously low level,
the under-voltage detector drives the MEM OK to the low
state, which in turn drives the BATON to the low state.
This shuts the supply down entirely. The entire supply
also shuts down when the power switch is turned off.