Power Supplies; +3V-Emi - GE MAC 5000 Service Manual

Power Supplies

+3V-C
+3V-M

+3V-EMI

+5V-M
+5V-EMI
Revision B
Equipment Overview: Theory of Operation
The MAC 5000 requires several regulated voltages for operation of its
various components. The Main Regulator provides most of the supply
rails. The supply rails are:
MAC 5000 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 5000 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 5000 is not fully in the 3V age. The Super I/O, floppy diskette
drive and thermal printhead all 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™ 5000 resting ECG analysis system
2024917-010
2-9