Power Supply Connections - Mallinckrodt NELLCOR NPB-4000 Service Manual

14.2 POWER SUPPLY CONNECTIONS

14.2.1 Voltages
Figure 14-1: Power Supply Connections
The power supply provides the power for the main board and all of the circuitry
in the system. It also contains control circuits for turning on and off the power,
as well as supplying the battery backup for the system.
The microprocessor and its associated circuits are powered from the regulated
3.3 volts DC generated on the power supply board. The 3.3 volts DC powers the
microcontroller, DRAM, flash, LCD controller and a portion of the LCD
contrast circuit, memory, the DUART, and real time clock. The 5 volts DC
powers the Nellcor knob, the TFT color display, and a portion of the speaker
circuit. The A/D converter is powered by its own 5 volt regulator. The 12 volts
DC powers the speaker circuit, the backlite inverter input voltage, and the op
amp for the battery voltage going to the A/D converter. The -24 volts is not
used. Typical current draws are as follows:
3.3 volts DC @ 300 mA
5.0 volts DC @ 260 mA
12.0 volts DC @ 315 mA
-24 volts DC @ 1.2 mA
Section 14: Main Color Board Digital Theory of Operation
14-3