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Valleylab Force FX-C - RF Leakage Reduction Circuit; REM Circuit; Isobloc Circuit

Valleylab Force FX-C
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Force
FXTM-C
Service
Manual
Power
SupplylRF
Board
RF
Leakage
Reduction
Circuit
FlJlglJrate
and
Spray
Coag
Modes
For
the
Fulgurate
and
Spray
coag
modes,
the
high
voltage
RF
output
pulse
repetition
period
varies
with
changes
in
spark
and
patient
tissue
impedance
to
limit
the
RF
leakage
current
to a
desired
level.
The
VSENSE
signal
is
obtc,ined
from
the
divider
(R58, R25)
located
on
the
primary
side
of
T4. VSENSE is
input
to a
negative
peak
detector
(U24A)
that
generates
the
analog
signal
(VPEAK-).
Then
U25A
amplifies
and
inverts
the
signal.
The
averaged
signal
(now
called
VPK+)
is
input
to
the
feedback
microcontroller
on
the
control
board
and
added
to
the
ECON
value
at
the
selected
power
setting.
The
sum
of
these
signals,
with
the
proper
gain
factors,
varies
linearly
with
load
impedance
at
the
patient
site.
This
sum
is
input
into
a
pulse
width
modulator
that
sends
its
output
(WAK\)
to
a
NAND
gate.
Thus,
the
T
__
ON\
signal
is
inhibited
for
up
to
four
consecutive
cycles.
Without
the
leakage
control,
the
pulse
repetition
period
is
171-1sec.
With
the
leakage
control
fully
activated,
the
total
pulse
train
repeats
every
84
ps
with
a
maximum
dead
time
of
600,,,
or
51 psec.
REM
Circuit
Components
U17
along
with
R95, R96, R97,
and
C79
form
a
precision
oscillator. R96
is
adjusted
for
the
frequency
that
will
produce
maximum
voltage
amplitude
(80 ± 10
kHz)
at
the
REM
connector
(J
17). R98 is a
temperahlre
compensating
thermocouple
that
cancels
temperature
drift
from
the
components
forming
the
oscillator.
The
REM
transformer
(TIO)
provides
isolated
reflected
impedance
sensing
for
tissue
impedance
across
the
REM
patient
return
electrode
terminals
(connected
to
]17,
pins
1
and
2).ln
addition
to
tuning
the
REM
circuit,
capacitors
C155, C156, C169,
and
C170
provide
a
return
path
for
high
frequency
RF
signals
through
CI57
to
the
RF
output
transfom1('r. TIle
REM
transformer
(TIO)
and
capacitors
C155,
Cl56,
C 169,
and
C170
form
a
resonant
circuit
with
a
nominal
operating
frequency
of
80
kHz.
Pin
1
of
TIO
clocks
the
active
synchronous
rectifier
formed
by
CMOS
switch
U28A.
This
device
is
closed
during
the
positive
period
of
the
REM_AC
signal
and
open
during
the
negative
period.
When
the
switch
is
closed,
Cl22
is
charged
to
the
peak
positive
value
of
REM_AC.
Then,
U318
amplifies,
filters
and
buffers
the
charge
on
C122
to
produce
the
R_SEN
signal.
The
microcontrollers
monitor
the
R_SEN siglUu
(which
is a
DC
voltage
proportional
to
imped<'illce)
to
determine
the
patient
return
electrode
status.
IsoBloc
Circuit
The
Iso
Bloc
circuit
provid.es a
means
of
detecting
a svvitch
closure
in
an
output
accessory
while
maintaining
electrical
isolation
between
the
generator
output
and
ground
referenced
circuitry.
The
IsoBloc
circuit
consists
of
an
isolated
DC
power
supply,
a
comparator
to
detect
svvitch
closure,
and
an
optoisolator
link
from
the
output
connected
circuitry
to
4-25

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