Backup Supply And Low Battery Disconnect; To Backup Switchover; Patient Module Voltage Regulator - HP PageWriter XL M1705B Service Manual

+5 Backup Supply and
The +5 backup supply (VBACK) provides power for DRAM and
Low Battery Disconnect
associated logic when the cardiograph is in Standby. When the
cardiograph is On and the $5 supply is in operation, the backup
supply is disabled and the $5 supply is connected to VBACK.
The low battery disconnect circuit will disconnect the battery
from the backup supply when the battery is approximately 80%
discharged. This will occur only when the cardiograph is in Standby
and is disconnected from AC power. The disconnect circuit is
disabled when UNITON is high. This avoids tripping the disconnect
circuit when battery voltage dips momentarily due to load.
Note .I
b?
When this circuit disconnects the battery, power to DRAM is lost,
resulting in the loss of system software and configuration data. The
software and configuration data must be reloaded from disk before
the cardiograph can be used.
+5 to Backup
At power-on, this circuit connects the +5 V supply to VBACK
Switchover
as soon as +5 V comes into regulation (+5READY goes high). At
power-off, this circuit disconnects +5 V from VBACK.
Patient Module Voltage
This circuit provides power (VFE) to the patient module. The
Regulator
regulator is enabled when UNITOFF (from the DRAM gate array)
goes low, and is disabled when UNITOFF goes high. Output voltage
is between 10.0 and 11.5 volts at 0 to 220 mA load. In the disabled
state, output voltage is about 1.3 volts while running off of AC, and
0 volts while running off of the battery.
Theory of Operation 5-21