Physio Control LIFEPAK 9 - Theory of Operation

LIFEPAK 9 defibrillator/monitor
Theory of
Operation
Power Supply PCB
Assembly (803726)
Power-On
Regulation
Overvoltage Protection
Output Isolation
Battery
This section contains detailed circuit descriptions of the Power Supply PCB,
Power Conversion PCB, Interconnect PCB, Main PCB, and Display
PCB/CRT Assemblies. Refer to schematic diagrams of these electrical
circuits in Section 5 while reading the circuit descriptions. Information about
selected integrated circuits (indicated by a >k on the schematic) is provided
in Section 6.
The Power Supply PCB converts input ac voltage to a nominal dc voltage for
the Power Conversion PCB and for charging the battery.
When ac current flows through J1, it is conditioned by RT1, L1, C2, C3, and
CRI. Resistor divider R1, R3, and R4 in series with parallel resistors R11
and R12 turn on Q1. Current builds in T1 primary windings (pins 4 and 6)
and is coupled with pins 1 and 2. Capacitor C6 couples the current build-up
into QI, causing saturation.
Increasing current through the TI primary produces voltage on the base of
Q2 and a voltage drop across parallel resistors R11 and R12. Q2 activation
overrides QI and terminates the primary current. Transformer T2 sustains
base drive current to Q2.
When battery voltage exceeds the voltage threshold set by VR1, Q4 turns on
and couples the voltage from T2 pins 4 and 5 to T2 pins 2 and 7. When
current subsides to proper levels, Q4 turns off, providing current feedback for
regulation.
If the regulation circuit fails, Silicon Controlled Rectifier (SCR) CR12,
together with CR13, R17, and R18, protects the load from damage. Diode
CR13 sets a voltage threshold which, when exceeded, triggers SCR CR12 to
short the Power Supply PCB circuit output. Removing ac power resets the
protection circuit.
Diode CR11 isolates the Power Supply PCB output from the filter network to
protect it from the battery voltage when ac power is removed. This is
necessary because the battery is connected in parallel with the Power Supply
PCB;
The 16Vdc, lead-acid battery is wired directly to the Power Supply PCB
output. The battery receives a constant charging current whenever the
instrument is connected to ac power and the rear panel mains power switch is
on. As the battery approaches full charge, the supply operates in constant
voltage mode. Current limiting sets the maximum charge current available to
All Rights Reserved
© August 1993 Physio-Control