Physio Control LIFEPAK 9 - Page 28

LIFEPAK 9 defibrillator/monitor
The Transfer Enable signal enables and maintains a constant current to the
Transfer Relay drive. The SWBATT voltage is stored in C9, enabling energy
transfer to occur with minimum battery voltage dissipation. Transistor Q4
and SCR CR4 control this voltage and direct it to the Transfer Relay. To
enable the relay drive, the signal from U14C turns on CR4. The signal from
ULIA forces U6A low, causing Q4 to conduct. With both CR4 and Q4
conducting, current starts to flow through R62. To maintain a constant
current to the Transfer Relay when current through R62 increases, the
noninverting input of U6A goes higher than the reference voltage at the
inverting input and the output switches high. This turns off Q4, causing the
current to decrease through R62 and switching U6A output low.
The high noise levels involved in the transfer of stored defibrillation energy
can jeopardize the function of many types of logic signals, particularly if any
are in transition from one state to another. To overcome this effect, the
System and Display/Recorder microprocessors and other high speed logic
components are rendered inactive during transfer. To accomplish this, U6B
discharges C35 at the input of comparator U8D and holds U8D low during
the time that the Transfer Relay coil is energized. The output of the U8D
remains low for an additional period to allow the Transfer Relay to reopen
and any stray current to dissipate. This signal, Sleep Inhibit, is used as a
logic activity enable.
Sleep Inhibit also clears the shift registers, U19 and U20. This sets all inputs
to U17B at OV, which inhibits the drive to the Energy Storage Capacitor
Charger. Inadvertent deactivation of the charge inhibit will then cause no
discharge of stored energy from the energy storage capacitor.
Energy Dump The Energy Dump circuit provides a safe current path for unused energy
stored in the energy storage capacitor. If the paddles are charged but not
discharged within one minute, the Energy Dump circuit is activated.
The internal dissipation of stored energy is accomplished with the dump
relay and a power resistor located within the Transfer Relay Assembly. The
dump relay is held in the normally closed condition by a permanent magnet.
When a charge is initiated, the contact opens to prevent the stored energy
from draining.
The System microprocessor controls Q3, preventing the paddles from being
charged for longer than one minute. Prior to any charge activity, the System
microprocessor holds the Dump Inhibit line low, keeping Q3 turned off and
the dump relay closed. During charging, the Dump Inhibit line is switched
high, turning on Q3 and opening the dump relay. If the one-minute charge
time-out expires or a different energy setting is chosen, the System
microprocessor turns Q3 off again to close the dump relay and dissipate the
Stored energy.
1-14 All Rights Reserved © August 1993 Physio—Control