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Physio Control LIFEPAK 9 - Page 44

Physio Control LIFEPAK 9
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LIFEPAK
9
defibrillator/monitor
1-30
Recorder
Power.
The
Recorder
Power
circuit
provides
operating
voltage
for
the
Printhead
and
the
Motor
Speed
Control
circuits
by
responding
to
a
high
logic
signal
from
the
Display/Recorder
microprocessor
at
the
base
of
Q2.
This
logic
signal
causes
Q2
to
conduct
which
turns
on
Q4,
thereby
supplying
power
for
the
recorder
motor
and
printhead.
Motor
Speed
Control.
Regulation
of
the
recorder
speed
is
necessary
because
of
the
variable
drag
on
the
recorder
motor
caused
by
the
thermal
printhead
and
the
lack
of
a
spindle
on
the
paper
roll.
The
paper
speed
of
the
recorder
is
regulated
by
a
variable-frequency,
pulse-width-modulation
circuit
that
compares
the
back
EMF
(electromotive
force)
on
the
motor
to
a
reference
voltage.
The
circuit
varies
the
frequency
of
the
motor
speed
drive
pulse
enough
to
maintain
the
25mm/s
paper
speed.
The
back
EMF
produced
in
the
motor
when
the
drive
pulse
switches
off
determines
the
speed
of
the
recorder
motor.
The
voltage
present
at
voltage
dividers
R18,
R17,
and
C4
is
directly
proportional
to
the
speed
of
the
motor
when
Q3
is
off.
A
frequency-modulated
pulse
from
transistor
Q3
drives
the
recorder
motor.
The
pulse
has
a
fixed
on-time
and
a
variable
off-time.
The
off-time
is
set
by
comparator
U2B
and
capacitor
C4
and
determines
how
much
power
Q3
conducts
to
the
motor.
The
fixed
on-time
is
determined
by
U2C.
When
the
off-time
period
is
over,
C2
has
charged
to
a
voltage
level
approximately
75%
of
VBATT.
At
the
next
on-time
cycle,
the
output
of
U2B
switches
to
ground,
the
voltage
at
U2C
pin
10
goes
to
about
1/3
of
VBATT,
and
C2
starts
discharging
through
R7.
U2C
changes
states
and
ends
the
pulse
on-time
when
the
voltage
on
C2
drops
below
the
voltage
on
pin
10.
The
voltage
on
U2B
pin
7
is
compared
to
a
calibrated
reference
voltage
at
pin
6
to
determine
the
off-time.
During
the
on-time,
C4
charges
to
a
voltage
proportional
to
the
battery
voltage.
During
the
off-time,
C4
discharges
toward
a
voltage
that
is
proportional
to
the
back
EMF
of
the
motor.
Under
normal
operating
conditions,
the
voltage
on
C4
discharges
over
several
time
constants
before
the
voltage
on
U2B
pin
7
is
equal
to
the
reference
voltage
on
pin
6.
When
the
voltages
are
equal,
the
output
of
U2B
switches
low
and
Q3
conducts,
supplying
voltage
to
the
motor.
As
the
load
on
the
motor
increases,
the
back
EMF
voltage
decreases
and
the
pulse-width
off-time
gets
shorter.
Printhead
Control.
Control
of
data
to
the
recorder printhead
is
accomplished
by
the
Display/Recorder
microprocessor
in
conjunction
with
Recorder
Gate
Array
U3,
Program
RAM
U13,
and
Program
EPROM
U14.
The
Display/Recorder
microprocessor
receives
data
from
the
System
microprocessor
and
formats
it
for
transmission
to
the
recorder
printhead.
The
Recorder
Gate
Array
receives
parallel
data
from
the
Display/Recorder
microprocessor
and
transmits
this
data
in
serial
form
to
the
recorder
All
Rights
Reserved
©
August
1993
Physio-Control

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