GE HEALTHCARE CARESCAPE Monitor B650 Technical Manual page 127

DC/DC Board
There are two versions of the DC/DC board: one for models with the optional battery and one
for models without battery. The non-battery version excludes the electronics needed for
battery charging and power path management.
The DC/DC board converts the output voltage of the AC/DC power supply, or the battery
voltage, to the following supply voltages:
• To +3.3 V supply voltage for the CPU board, LCD display, user interface board and the
standard/advanced interface board using a step-down converter.
• To + 5 V supply voltage for the CPU board, user interface board and the
standard/advanced interface board using a step-down converter.
• To +12 V supply voltage for the optional recorder and the LED backlight of the display
using a buck-boost converter.
• To + 15VMod supply voltage for the PSM module and the E-Module interface board using
a buck-boost converter. This converter is omitted in the non-battery models, where the
+15VMod power line is connected directly to the VSYS voltage.
• It passes the 8.7 -16 V (in AC/DC use 14.9-16 V) VSYS supply voltage for the E-Module
interface board, the 10-pin ePort connector in the PDM docking station and for the DB9
ePort connector in the advanced interface board. The power supply is capable to supply
VSYS voltage only to one ePort connector at a time.
• All supply voltages have over-voltage and short-circuit protection.
The DC/DC board takes care of the battery charging and controlling of the power path
switches. The power path switches select either AC/DC output voltage or battery voltage as the
DC/DC board input source.
The DC/DC board PMC CPU (Power Management Controller) controls power supplies'
sequencing. It measures board temperature and voltages by an internal A/D converter. System
and module currents also are measured and the corresponding power consumptions
calculated. PMC communicates with the CPU board via serial communication and with the
battery and battery charger IC via SM Bus. I2C bus (Inter-Integrated Circuit) is used for
communication with the A/D-converters and temperature sensors on the other boards of the
patient monitor.
The smart battery charger acts as an SM Bus slave device that responds to charging current
and charging voltage requests received via SM Bus. The charging requests are not sent directly
by the smart battery, but by the PMC CPU, which first asks the values from the battery. The PMC
may reduce or stop charging current if needed from the system point of view, i.e., if system
power consumption or temperature would get too high. The smart battery is responsible for
the charging algorithm and capacity calculation.
The battery charger has input current HW-limit feature. In a case where the input current
would exceed the limit, the charger reduces the output current to keep the input within the
limit. The AC/DC current for the whole system is taken through this current measurement as
well. This results in the charger reducing its output current if the sum of the charger input
current and system current exceeds the input limit. The purpose of this is to prevent the AC/DC
power source from getting overloaded if system power rapidly increases during charging.
Cooling
The patient monitor uses convection cooling. The ventilation openings of the device are located
in the rear of the monitor and below the keypad.
The AC/DC power supply unit has a heat sink that is mounted to the aluminum rear unit
assembly to enhance cooling of the power supply.
Theory of operation
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