Data General NOVA 4/S Manual page 99

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PROTECTION
> +12V MEM
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ye) LINEAR +5V MEM
71 CIRCUIT
Operation
MEM OK, and the INT POK signals to determine when
ac power fails and when ac power recovers. If INT PF
goes to the low state when MEM OK is in the high state,
power is failing. The battery switch turns on the
battery to supply power (BATT) to the rest of the battery
backup circuitry. When the power recovers, INT PF goes
to the high state. Shortly, the voltage outputs from the
basic power supply come up and cause INT POK to go to
the high state. If the battery is on when the outputs
recover, MEM OK is in the high state; if the battery is
off, MEM OK goes to the high state. When both INT POK
turns off the battery.
The linear regulating circuit regulates the battery's
output voltage to produce the +5V MEM output. This
circuit is a series pass regulator with current limiting.
The pulse width modulation control governs the amount
of power supplied to the flyback converter. It opens
and closes the power path between the battery and the
flyback converter once every 50 us (at a 20 KHz rate)
closed time (the duty cycle) in accordance with the
variation on the+l12V MEM output of the flyback
regulator. In this way, the pulse width modulation
control regulates the +12V MEM output.
The flyback converter transforms the 6V de output
from the battery into a regulated +12V MEM output
and a -5V MEM output.
The over current detector is a cycle by cycle current
limiter. When it detects an over current condition, it
shuts down the pulse width modulation control for one
cycle (50 us).
The discharge protection circuit monitors the voltage
level of the battery. When it drops below 5.4 volts, the
discharge protection circuit turns off the battery to
prevent it from degrading.
The battery charger recharges the battery when the
basic power supply is operating.