Power Supplies; +3V-Emi - GE MAC 5500 Service Manual

Power Supplies

+3V-C
+3V-M

+3V-EMI

+5V-M
+5V-EMI
2-10
Equipment Overview: Theory of Operation
The MAC 5500 resting ECG analysis system requires several regulated voltages
for operation of its various components. The Main Regulator provides most of the
supply rails. The supply rails are:
MAC 5500 resting ECG analysis system is never truly "off." The system
supervisor microcontroller (MOE) must constantly monitor the power key and
perform battery charging/gauging. The clock/calendar in the Super I/O chip must
also maintain time/date when the machine is off. These functions are powered from
the +3V-C rail, which provides power continuously from the battery pack regardless
of the state of the rest of the system. The Main Regulator produces +3V-C directly
from the battery rail via an internal low current linear regulator. Only 5mA are
available from +3V-C, so it must be used sparingly.
NOTE
The MAX782's low current regulator is dreadfully inefficient. Regulator Q
current appears to be about 3x the load current. This makes conservation of load
on +3V-C crucial.
Most of the MAC 5500 hardware runs from +3V-M. The MAX782 provides this rail
from the battery via a PWM synchronous switching regulator. Moe controls +3V-M
in tandem with +5V-M.
This is simply an RF blocked feed from +3V-M. +3V-M load is contained within the
CPU board. Power for devices for external functions is supplied by +3V-EMI. The
isolation of +3V-EMI from +3V-M may be unnecessary as the concept has never
been tested for its effect.
The MAC 5500 resting ECG analysis system is not fully in the 3V age. The Super
I/O and thermal printhead require 5V power. The MAX782 provides this rail via
another PWM synchronous switching regulator. Moe controls +5V-M in tandem
with +3V-M.
Similar to +3V-EMI, this rail is an RF blocked feed from +5V-M, used to power
devices for external functions. The isolation of +5V-EMI from +5V-M may be
unnecessary as the concept has never been tested for its effect.
MAC 5500 resting ECG analysis system
2020299-020
Revision E