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Valleylab Force FX-C - Page 73

Valleylab Force FX-C
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Force
F)(TM-C
Service
Manual
Power
Supply/RF
Board
L-C filter is
tuned
just
slightly
higher
than
the
RF
s'witching frequency,
achieving
a
high
degree
of
filtering.
The
output
is
very
sinusoidal
over
the
full
range
of
load
impedances.
Capacitors
C34
and
en
are
tuned
with
the
RF
transformer
primary
so
that
the
flyback
voltage
appearing
across
the
MOSFET
at
turn
off is a
half
sine
pulse
and
returns
to
zero
volts
before
the
next
cycle
begins.
The
T_.ON\
pulse
width
is
chosen
to
support
this
hilling.
This
zero
voltage
switching
improves
the
efficiency
of
the
RI;
stage
and
is effective
over
a
wide
range
of
load
impedances.
The
circuit topology
of
tlle Blend
cut
mode
is
the
same
as
the
Pure
cut
mode.
In
Blend
mode,
ho,·vever, the T _
ON
\
signal
is
an
interrupted
pulse
train
with
a 50%
duty
cycle
and
a
pulse
train repetition rate
of
27 kHz. For a
given
power
setting, Blend gives a higher
peak
current,
providing
better hemostasis
thiUl
Pure
or
Low.
To
minimize ringing
at
the
beginning
of
the off
period
of
the
Blend
waveform
envelope,
the
damping
resistor is switched
on
just before
switching
ends
and
stays
on
for
part
of
the
off period.
Bipolar
Modes
The
circuit
topology
for
the
bipolar
modes
is essentially
the
same
as
the
cut
modes,
except
the
output
voltage
is
tapped
off C152
and
the
switching
frequency
is 470
kHz.
These
differences
allow
for
the
higher
currents
and
lower
voltages
required
in
bipolar
surgery
while
still
maintaining
the
advantages
of
zero
voltage
switching
in
the
MOSFET.
The
T_ON\
signal
is
a
continuous
pulse
train
with
a 423
ns
pulse
width.
Coag
Modes
In
the
Fulgurate
and
Spray
coag
modes,
K2
is
set
so
that
diode
CR2
blocks
reverse
current
in
the
power
MOSFET, C40
as
well
as
C34
,md
C41
are
across
the
MOSFET,
and
the
transformer
primary
consists
of
winding
1-2
only.
Kl4
is
open,
keeping
the
series
capacitor
bank
(C15O-C152,
and
C159)
out
of
the
circuit.
In
the
LCF
Fulgurate
coag
mode,
the
T_ON\
signal
is a
continuous
pulse
train
with
a
pulse
width
of
1.69
}Is
and
a
frequency
of
57
kHz.
When
the
MOSFET
turns
on,
some
energy
is
delivered
to
the
output
and
some
is
stored
in
the
T4 core. 'When
the
MOSFET
is
turned
off,
the
energy
stored
in
the
core
out
with
a
frequency
of
591
kHz.
The
frequency
is
set
by
C34, C40, C41, "md
the
inductance
of
winding
1-2
of
T4. CR2
blocks
reverse
current
in
the
body
drain
diode
of
the
MOSFET so
that
the
power
waveform
can
ring
negative.
This
allows
high
peak
voltages to
be
achieved
at
the
output.
In
most
cascs, all
the
energy
stored
in
the
transformer
core
during
one
switching
cycle is
delivered
to
tlle
load
before
the
next
cycle begins.
The
Fulgurate
mode
works
the
same
as
the
LCF
Fulgurate
mode,
except
the
T_ON\
signal
is a
continuous
pulse
train
with
a
pulse
width
of
1.69 }IS
and
a
frequency
of
30
kHz.
The
Spray
mode
works
essentially
the
same
as
the
Fulgurate
mode,
except
the
T_ON\
pulse
frequency
is
randomized
over
the
range
of
21.6
kHz
to
35.23
kHz.
In
addition,
amplifier
U7
A
randomly
varies
the
output
amplitude
by
10'70.
The
ECON-GAIN
signal
from
the
Control
board
the
gain
of
U7 A
between
1
and
L
1.
4-23

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