Physio Control LIFEPAK 9 - Microcontroller Core

LIFEPAK 9 shock advisory adapter Service Manual
1-6
Theory of Operation
SAS Adapter PCB
Assembly (803779)
Power Supply
Preamp
The
following
paragraphs
describe
the
SAS
Adapter
PCB.
Schematic
diagrams
of
these
electrical
circuits
in
Section
5
should
be
referred
to
while
reading.
Section
6
contains
additional
information
about
selected
ICs
(indicated
by
a
>K
on
the
schematic)
to
aid
in
circuit
analysis
and
troubleshooting.
The
SAS
Adapter
PCB
contains
all
of
the
electrical
components.
The
five
primary
circuits
are:
e Power Supply
e Preamp
e Microcontroller Core
e Instrument Interface
e Microcontroller Inhibit.
The Power Supply circuit provides isolated and nonisolated power for all
circuits on the SAS Adapter PCB. Pulse-width modulator U2 drives the
isolated supplies; transformer T1 provides patient isolation.
Pulse-width modulator U2 alternately turns on transistors Q3 and Q4
from outputs QA and QB. The outputs of both transistors are isolated
across T1 (slightly stepped down) and rectified by CR6 and CR7,
providing isolated voltage for the regulators and opto-isolators.
Regulator U8 reduces the isolated voltage to +8V for the preamp
operating voltage. General +5V VREF power throughout the SAS
Adapter PCB is regulated by U9. Regulator U10 reduces the isolated
voltage for all digital microcircuits. Operating voltages for the
nonisolated components are provided by regulator U3.
The Preamp circuit amplifies the ECG signal and determines the patient
impedance before the microcontroller analyzes the ECG.
Microcontroller U17 automatically stops analyzing the incoming ECG
signal whenever predetermined patient impedance levels are exceeded.
This could be due to uneven paddle contact with the patient or excessive
motion. Both Preamp circuit functions are performed mainly by custom
hybrids U19 and U18. Hybrid U18 amplifies the ECG signal; identical
hybrid U19 determines patient impedance.
Input protection for the custom hybrids is essential, since they are
connected directly to the paddles. Positive and negative transients are
shunted to ground by CR2 through CRS. Resistor R31 limits the current
to both hybrids. Additional input protection for U19 is provided by
VSP2, C27, and R22.
All Rights Reserved © November 1994 Physio-Control Corporation