Battery Operation And Condition - HP PageWriter XL M1705B Service Manual

Battery Charger and
The battery charger converts VIN (15 to 31 volts) to VBAT (20 to 22 q
Battery Sensor
volts). VBAT connects to the f terminal of the battery through a
fuse, which is located on the CPU assembly. The battery connects to
the CPU assembly at J4. Pin assignments for the battery connector
are listed in Appendix A, "Connector Pin Assignments."
The
converter is of the "buck-boost" type. It is actually a "buck" rectifier
connected to a "boost" (step-up) regulator so that the output voltage
can be higher or lower than the input voltage.
Two circuits provide current limiting. One limits charging current
to the battery to 1.7 amps average. The other current limit circuit
limits the charger output current to a peak 5 amps. This has two
purposes:
n
To limit peak current during power-on and power-off.
n
To limit peak current from the battery charger during printer
power-on. When the printer turns on, it can draw peaks of current
as high as 20 amps. The battery and battery charger provide this
current. This current limit circuit helps prevent overstressing the
switching PETS. )
There are two output voltage modes, cycle and float. The charger
enters cycle mode when the charging current exceeds 400 to 700
mA. In cycle mode, the output voltage is fixed at approximately 21
to 22 volts. The charger enters float mode when charging current
is less than 400 to 700 mA. In float mode, the output voltage
varies inversely with battery temperature. The charger determines
temperature by measuring a. voltage across a thermistor in the
battery.
Battery Operation and Condition
When operating on battery power, the cardiograph software monitors
the battery and displays the amount of charge remaining on the
front panel battery indicator. When the low battery indicator on
the front panel illuminates, the battery has discharged to the low
battery warning point. The cardiograph can continue to operate in
this condition until it reaches
the
low
battery
shutdown point.
-1,
5-18 Theory of Operation