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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention in general relates to electrosurgery, and in particular to an
electrosurgical unit that produces a high power output at the
electrosurgical electrodes.
2. Description of the Prior Art
Electrosurgical generators which produce high frequency electric currents
for cutting of tissue and coagulation of small blood vessels have been
well-known for several generations. It has also been well-known that
different types of waveforms produce different types of electrosurgical
functions. In modern electrosurgery, these functions are generally broken
down into two primary functions, coagulation and cut, with coagulation
being a process in which small blood vessels are sealed by controlled
electrical cauterization, and cut being a process in which tissue and
vessels are severed by electrical energy. Generally these two functions or
modes, cut and coagulation, are broken down into two further modes
commonly called fulgration and blend. Fulgration is a form of coagulation
in which the electrode is spaced from the tissue to be coagulated and
sprays electrical energy over a large area of tissue, in contrast to
"pure" coagulation in which the electrode is touched to the tissue to
coagulate the tissue which the electrode touches. Blend is a mode which
combines both cut and coagulation, therefore allowing the surgeon to cut
and coagulate at the same time. It is known that the desirable output
power and voltage at the electrodes for a cutting or coagulation procedure
varies depending upon the depth of cut, the impedance provided by the
tissue and other substances between the electrodes, and numerous other
factors. Thus, electrosurgical units have been designed to provide various
means of controlling power and the amplitude of the output voltage at the
electrodes. Generally, two approaches have been taken to provide the
appropriate power and voltage control. In one approach, separate
electronic circuits inherently capable of producing different power and
voltage levels are included in one electrosurgical unit and switches are
used to connect the different circuits to the electrodes. See, for
example, U.S. Pat. Nos. 3,952,748 issued to Paul L. Kaliher, et al. and
3,964,487 issued to Donald W. Judson. In another approach, a voltage
representative of the output voltage is sensed and is fed back into the RF
signal generation circuitry to obtain a "constant" output voltage under
changing load conditions. See, for example, U.S. Pat. Nos. 4,092,986
issued to Max Schneiderman, 3,875,945 issued to Joshua Friedman and
4,126,137 issued to G. Kent Archibald. The former approach is quite
effective, but results in a complex and bulky electrosurgical generator.
It also requires switching between the coagulation and fulgration modes,
which is often inconvenient, since surgeons may desire to switch back and
forth between the two modes rapidly, and often. The latter approach does
not yield a satisfactory output voltage for all functions and conditions
desired by a surgeon, and is relatively inefficient, resulting in more
heat dissipation from the unit than is desirable.
It is known in the art to employ transformers in coupling power to the
electrodes. Electrosurgical units have employed conventional transformers
in which the windings of the primary and secondary are overlaid.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new approach to
controlling the voltage at the output electrodes.
It is a further object of the invention to provide an electrosurgical unit
having a characteristic voltage response at its electrodes that is more
synergistic with normal surgical operating procedures.
It is a further object of the invention to provide an electrosurgical unit
meeting one or more of the above objects which is also more efficient than
prior art electrosurgical generators.
It is another object of the invention to provide an electrosurgical unit
having power output and low current leakage.
It is another object of the invention to provide an electrosurgical unit
meeting one or more of the above objects and having a transformer having
high magnetic coupling and low capacitive coupling.
It is still another object of the invention to provide one or more of the
above objects in an electrosurgical unit that is simpler, more compact,
and less expensive than prior art electrosurgical units.
The invention provides an electrosurgical unit for producing an
electrosurgical output signal, the unit comprising sensing means for
providing a signal representative of the voltage of the electrosurgical
output signal, mode setting means for changing between a first mode
setting and a second mode setting, generator means responsive to the mode
setting means for providing a first output signal waveform when the mode
setting means is in the first mode and a second output signal waveform
when the mode setting means is in the second mode, means responsive to
said mode setting means for producing a mode signal, means responsive to
the sensing means signal for limiting the output signal voltage, and means
responsive to the mode signal for suppressing the operation of the means
for limiting. Preferably the generating means includes a transistor having
a control terminal for controlling the electrical flow through the
transistor, the means for limiting comprises a transistor voltage limiting
means for limiting the voltage applied to the control terminal of the
transistor, and the means for suppressing comprises a means for preventing
the transistor voltage limiting means from operating in the second mode.
Preferably the first mode is a cut mode and the second mode is a
coagulation mode. Preferably the generator includes a transformer having a
high ratio of secondary to primary turns. In the preferred embodiment the
ratio is 8 to 1; it is desirable that it be at least 2 to 1.
In another aspect the invention provides an electrosurgical unit which
includes a transformer having primary and secondary windings that are
wound concentrically about the same axis and are spaced from each other
along the axis.
The invention provides an electrosurgical unit that is simple, effective
and efficient. The unit also provides a characteristic voltage at the
output that is more synergistic with normal surgical procedures. Normally,
the surgeons apply the fulgration mode with the active electrosurgical
electrode spaced from the tissue to be fulgrated, and apply the
coagulation and cutting modes with the electrode in contact with the
tissues. The action of the voltage limiting circuitry prevent high
voltages from being produced in cut mode as is desirable. However the fact
that the voltage limiting action is suppressed in the coag mode permits
high voltages to normally develop in the circuit in the coag mode when the
electrode is spaced from the tissue. These high voltages automatically
give rise to the fulgration mode under such conditions. Numerous other
aspects, features, objects and advantages of the invention will now become
apparent from the following detailed description when read in conjunction
with the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A through 1C are a block diagrammatic illustration of a preferred
embodiment of the invention; the full electrosurgical unit may be seen by
placing FIG. 1A on the left, FIG. 1B in the center and FIG. 1C on the
right, in which positions the interconnections between the Figs. are
evident;
FIG. 2 shows an electrical circuit diagram of the basic hybrid cascode
amplifier according to the invention;
FIG. 3 is detailed electrical schematic of the hybrid cascode power
amplifier of the preferred embodiment of the invention shown in FIG. 1C;
FIG. 4 is a detailed electrical schematic of the output stage of the
embodiment of the invention shown in FIG. 1C;
FIG. 5 shows the core of the bipolar transformer utilized in the embodiment
of FIG. 4;
FIG. 6 illustrates the method of winding the primary winding on the core of
FIG. 5;
FIG. 7 shows the method of winding of the secondary winding on the core of
FIG. 5;
FIG. 8 is a partial sectional view of the monopolar transformer utilied in
the embodiment of FIG. 4;
FIG. 9 is an external view of the transformer of FIG. 8;
FIG. 10 is a partial sectional end view of the transformer of FIG. 9;
FIG. 11 is a detailed electrical schematic of a portion of the Power Supply
of the embodiment of the invention in FIG. 1A;
FIG. 12 is the power-on reset circuitry of the embodiment of the invention
shown in FIG. 1A;
FIG. 13 is a detailed electrical schematic of the lamp/relay register of
the embodiment of the circuitry shown in FIG. 1A;
FIG. 14 is a detailed electrical schematic of the Gate Waveform
Generator/Driver of the embodiment of the invention shown in FIG. 1B;
FIG. 15 and FIG. 16 show a detailed electrical schematic of the Base
Voltage Generator/Driver of the embodiment of the invention shown in FIG.
1B.
FIG. 17 is a detailed electrical schematic showing the connections to the
microprocessor in the embodiment of the invention shown in FIG. 1A;
FIG. 18 is a block diagram of the microprocessor; and
FIG. 19 is a diagram showing the waveform generator counter states at
specified times of the counter cycle.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1A through 1C, an electrosurgical unit according to the
preferred embodiment of the invention is shown. The blocks shown are
divided along functional boundaries. The schematic diagrams in the
following Figs. are divided along the same functional lines where
possible. Connections across physical boundaries are shown where they
apply. Foot switches 10, hand switches (not shown) connected through
outputs 22, front panel switches 10c and 10d and end potentiometers 14
(FIG. 1A) control controller circuitry 20 to provide the desired
electrical mode settings within the unit and thus control the electrical
power signals at outputs 22 (FIG. 1C). The Cut and Coagulation mode
settings are activated via the handswitches and the footswitches 10 which
are conventional in electrosurgical units and will not be described
further herein. A power amplifier 23 comprising transistors 24 and 25
provides the electrical power to the outputs 22 through output circuitry
30. The Base Voltage Generator/Driver (BVG) 34 supplies base current to
the power amplifier transistor 24 at a voltage appropriate to the mode of
operation. It includes means 92, 95, 111 (see below) for limiting the
voltage at the electrodes 22. The Gate Waveform Generator/Driver 33 (WFG)
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