Battery Backup Option - Data General NOVA 4/S Manual

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The power fail detector monitors the 300 VNR source
When it detects an under voltage condition, it pulls the
signal to the low state to inform the system of an
impending ac power failure. Approximately 22 ms later,
state for 155 ms or longer depending on how long the
Whenever, INT POK goes to a low state, it drives PWR OK
to a low state to reset the CPU. If battery backup is not
and later, it drives MEM OK to the low state. If battery
backup is present, PWR OK stays in the low state and
MEM OK stays in the high state as long as the battery lasts.
Over Voltage Detection
The over voltage detector protects against over voltage
conditions on the +5V, +12V,and +15V outputs. If any of
these outputs goes above the shut down level (see Table
10.2), this detector shuts the pulse width modulation
control down permanently. The pulse width modulator
control will not start again until the power supply is
turned off and on again using the front console power
switch. This over voltage fault also discharges the
capacitor in the soft start logic to allow the voltage outputs
to come up slowly when the system is powered up again.
OVER VOLTAGE SHUTDOWN LEVELS
Output Shutdown Voltage
+5V 5.66 +/- 1%
+12V 13.56 +/-5%
+15V 17.3 +/-5%
Over Current Detection
The main over current protection device is a cycle by
cycle current limiter. It consists of a current sense
transformer T3 in the inverter and an over current
detector. The over current detector monitors the current
in the secondary winding of this transformer. When the
current flowing in this winding is too great, the over
current detector shuts the pulse width modulation
control down for one cycle (50 usec).
A secondary over current protection device, the current
limiter, monitors the current on the +12V, +15V,
and +12V MEM outputs. When the sum of the current
on these three outputs goes above 5 Amps, the current
limiter temporarily shuts down the pulse width
modulation control. Although the shutdown time will
vary with the load on these outputs, it is typically 0.5
sec. This over current fault also discharges the capacitor
in the soft start logic to allow the voltage outputs to
come up slowly when the fault condition is removed.
Two reed switches with a one turn winding around
them function as current sensors for the +5V outputs.
When the current on either of the two +5V outputs,
goes above 20-25 Amps, the reed switches temporarily
shut down the pulse width modulation control. This
over current fault also discharges the capacitor in the
soft start logic to allow the voltage outputs to come up
slowly when the fault condition is removed.
BATTERY BACKUP OPTION
The battery backup option generates 6-volt de power
for the optional battery backup circuitry. This circuitry
maintains the following critical memory voltages when
a power failure occurs: +5V MEM, +12V MEM, and
-0V MEM. These voltages are needed to refresh data
stored on the dynamic RAM memory board. In
addition, the battery backup circuitry powers the
systems clocks and the front console lights, and
provides a memory status signal (MEM OK) to indicate
when the memory voltages are above the minimum
operating levels.
Besides the battery, the battery backup option consists
of a battery switch, a linear regulating circuit, a pulse
width modulation control, flyback converter, several
protection circuits, and a battery charger. Figure 10.2
shows the interconnection between these components.