Method and system of an electrosurgical controller with wave-shaping

An electrosurgical controller with wave-shaping. At least some embodiments are methods including generating an alternating current (AC) voltage signal within an electrosurgical controller. The generating may be by inducing an intermediate AC voltage signal on a secondary winding of a first transformer, and wave-shaping the intermediate AC voltage signal by a second winding of a second transformer coupled to the first transformer, and thereby creating a final AC voltage signal. Thereafter, the method includes applying the final AC voltage signal to electrical pins of a connector configured to couple to an electrosurgical wand.

CROSS-REFERENCE TO RELATED APPLICATIONS

BACKGROUND

Electrosurgical systems are used by physicians to perform specific functions during surgical procedures. For example, in an ablation mode electrosurgical systems use high frequency electrical energy to remove soft tissue such as sinus tissue, adipose tissue or other tissue such as meniscus, or cartilage or synovial tissue in a joint. In a coagulation mode, the electrosurgical device may aid the surgeon in reducing internal bleeding by assisting in the coagulation and/or sealing of vessels. In both the ablation and coagulation mode, control of the electrical energy to provide a proper ablation and/or coagulation is utilized, and thus any advance that increases the energy control functionality of an electrosurgical system provides competitive advantage.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies that design and manufacture electrosurgical systems may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function.

“Active electrode” shall mean an electrode of an electrosurgical wand which produces an electrically-induced tissue-altering effect when brought into contact with, or close proximity to, a tissue targeted for treatment, and/or an electrode having a voltage induced thereon by a voltage generator.

“Active terminal” shall mean an electrical connection to a transformer that is configured to couple to an active electrode of an electrosurgical wand.

“Return electrode” shall mean an electrode of an electrosurgical wand which serves to provide a current flow path for electrons with respect to an active electrode, and/or an electrode of an electrosurgical wand which does not itself produce an electrically-induced tissue-altering effect on tissue targeted for treatment.

“Return terminal” shall mean an electrical connection to a transformer that is configured to couple to a return electrode of an electrosurgical wand.

“Center tap”, in relation to a transformer, shall mean an electrical connection to a winding of the transformer at approximately the middle turn of the total number of turns; however, the center tap need neither be precisely at the numeric middle nor the physical middle, and a tap that is within 5% of the total number of turns from the numeric middle shall be considered a center tap.

“Fixed”, in relation to a direct current (DC) voltage level applied to a winding of a transformer, shall mean a DC voltage level that is either: controlled to a particular DC voltage level during changes in load seen by a secondary of the transformer; or is not adjusted to be a different voltage level in spite of changes in load seen by the secondary of the transformer. The presence of noise (e.g., alternating current (AC) ripple voltages) “riding” the DC voltage level, and drops in voltage caused by current draw of the primary winding, shall not obviate the status of a DC voltage as fixed.

“Different than” in the claims shall mean only that the different devices are individual physical devices. “Different than” shall not be construed to require that the devices are of different construction or configuration. Thus, for example, “a first transformer, different than a second transformer” shall mean that two physical transformers are present, and the two transformers may be of identical physical construction, or different physical construction

Where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein.

All existing subject matter mentioned herein (e.g., publications, patents, patent applications and hardware) is incorporated by reference herein in its entirety except insofar as the subject matter may conflict with that of the present invention (in which case what is present herein shall prevail). The referenced items are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such material by virtue of prior invention.

DETAILED DESCRIPTION

Before the various embodiments are described in detail, it is to be understood that this invention is not limited to particular variations set forth herein as various changes or modifications may be made, and equivalents may be substituted, without departing from the spirit and scope of the invention. As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. All such modifications are intended to be within the scope of the claims made herein.

FIG. 1illustrates an electrosurgical system100in accordance with at least some embodiments. In particular, the electrosurgical system comprises an electrosurgical wand102(hereinafter “wand”) coupled to an electrosurgical controller104(hereinafter “controller”). In some embodiments the wand102comprises an elongated shaft106that defines distal end108where at least some electrodes are disposed. The elongated shaft106further defines a handle or proximal end110, where a physician grips the wand102during surgical procedures. The wand102further comprises a flexible multi-conductor cable112housing a plurality of electrical leads (not specifically shown inFIG. 1), and the flexible multi-conductor cable112terminates in a connector114. Though not visible inFIG. 1, in some embodiments the wand102has an internal passage fluidly coupled to a flexible tubular member116. The internal passage and flexible tubular member116may be used as a conduit to supply conductive fluid to be proximate to the distal end108, or the internal passage and flexible tubular member may be used to aspirate the area proximate to the distal end108of the wand102. Other wand types may be equivalently used.

The wand102couples to the controller104, such as by a wand connector120on an outer surface122of the controller104(in the illustrative case ofFIG. 1the front surface). A display device or interface panel124is visible through the outer surface122, and in some embodiments a user may select operational modes of the controller104by way of the interface panel124and related buttons126. In some embodiments the electrosurgical system100also comprises an interface device in the form of a foot pedal assembly130. The foot pedal assembly130may comprise one or more pedal devices132and134, a flexible multi-conductor cable136and a connector138. While only two pedal devices132,134are shown, any number of pedal devices may be implemented. The outer surface122of the controller104may comprise a corresponding pedal connector140that couples to the connector138. A physician may use the foot pedal assembly130to control various aspects of the controller104. For example, a pedal device, such as pedal device132, may be used for on-off control of the application of radio frequency (RF) energy to the wand102. As yet another example, a pedal device, such as pedal device134, may be used to modify a characteristic of the RF energy delivered to the wand102, such as by a change in the applied voltage or the shape as a function of time of the voltage of the RF energy.

The electrosurgical system100of the various embodiments may have a variety of operational modes. One such mode employs Coblation® technology. In particular, the assignee of the present disclosure is the owner of Coblation® technology. Coblation® technology involves the application of RF energy between one or more active electrodes and one or more return electrodes of the wand102to develop high electric field intensities in the vicinity of the target tissue. The electric field intensities may be sufficient to vaporize an electrically conductive fluid over at least a portion of the one or more active electrodes in the region between the one or more active electrodes and the target tissue. The electrically conductive fluid may be inherently present in the body, such as blood, or in some cases extracellular or intracellular fluid. In other embodiments, the electrically conductive fluid may be a liquid or gas, such as isotonic saline. In some embodiments the electrically conductive fluid is delivered in the vicinity of the active electrodes and/or to the target site by the wand102, such as by way of the internal passage and flexible tubular member116.

When the electrically conductive fluid is heated to the point that the atoms of the fluid vaporize faster than the atoms condense, a gas is formed. When sufficient energy is applied to the gas, the atoms collide with each other causing a release of electrons in the process, and an ionized gas or plasma is formed (the so-called “fourth state of matter”). Stated otherwise, plasmas may be formed by heating a gas and ionizing the gas by driving an electric current through the gas, or by directing electromagnetic waves into the gas. The methods of plasma formation give energy to free electrons in the plasma directly, electron-atom collisions liberate more electrons, and the process cascades until the desired degree of ionization is achieved. A more complete description of plasma can be found in Plasma Physics, by R. J. Goldston and P. H. Rutherford of the Plasma Physics Laboratory of Princeton University (1995), the complete disclosure of which is incorporated herein by reference.

As the density of the plasma becomes sufficiently low (i.e., less than approximately 1020 atoms/cm3for aqueous solutions), the electron mean free path increases such that subsequently injected electrons cause impact ionization within the plasma. When the ionic particles in the plasma layer have sufficient energy (e.g., 3.5 electron-Volt (eV) to 5 eV), collisions of the ionic particles with molecules that make up the target tissue break molecular bonds of the target tissue, dissociating molecules into free radicals which then combine into gaseous or liquid species. Often, the electrons in the plasma carry the electrical current or absorb the electromagnetic waves and, therefore, are hotter than the ionic particles. Thus, the electrons, which are carried away from the target tissue toward the active or return electrodes, carry most of the plasma's heat, enabling the ionic particles to break apart the target tissue molecules in a substantially non-thermal manner.

By means of the molecular dissociation (as opposed to thermal evaporation or carbonization), the target tissue is volumetrically removed through molecular dissociation of larger organic molecules into smaller molecules and/or atoms, such as hydrogen, oxygen, oxides of carbon, hydrocarbons and nitrogen compounds. The molecular dissociation completely removes the tissue structure, as opposed to dehydrating the tissue material by the removal of liquid within the cells of the tissue and extracellular fluids, as occurs in related art electrosurgical desiccation and vaporization. A more detailed description of the molecular dissociation can be found in commonly assigned U.S. Pat. No. 5,697,882 the complete disclosure of which is incorporated herein by reference.

In addition to the Coblation® mode, the electrosurgical system100ofFIG. 1is also useful for sealing larger arterial vessels (e.g., on the order of about 1 millimeter (mm) in diameter), when used in what is known as a coagulation mode. Thus, the system ofFIG. 1may have an ablation mode where RF energy at a first voltage is applied to one or more active electrodes sufficient to effect molecular dissociation or disintegration of the tissue, and the system ofFIG. 1may also have a coagulation mode where RF energy at a second, lower voltage is applied to one or more active electrodes (either the same or different electrode(s) as the ablation mode) sufficient to heat, shrink, seal, fuse, and/or achieve homeostasis of severed vessels within the tissue.

The energy density produced by electrosurgical system100at the distal end108of the wand102may be varied by adjusting a variety of factors, such as: the number of active electrodes; electrode size and spacing; electrode surface area; asperities and/or sharp edges on the electrode surfaces; electrode materials; applied voltage; current limiting of one or more electrodes (e.g., by placing an inductor in series with an electrode); electrical conductivity of the fluid in contact with the electrodes; density of the conductive fluid; and other factors. Accordingly, these factors can be manipulated to control the energy level of the excited electrons.

FIG. 2shows a cross-sectional view of wand102in accordance with at least some embodiments. In particular,FIG. 2illustrates the elongated shaft106comprising distal end108and proximal end110. Distal end108comprises a plurality of electrodes200. The electrodes ofFIG. 2are merely illustrative, and any arrangement of electrodes may be equivalently used. Each electrode200has an electrical lead associated therewith that runs through the elongated shaft106to the flexible multi-conductor cable112. In particular, electrode200A has dedicated electrical lead202A which runs within the elongated shaft to the become part of cable112. Similarly, electrode200B has dedicated electrical lead202B which runs within the elongated shaft106to become part of cable112. Illustrative electrodes200C and200D likewise have dedicated electrical leads202C and202D, respectively, which run within the elongated shaft106to become part of cable112. In some embodiments, the elongated shaft106has dedicated internal passages (in addition to optional internal lumen250) through which the electrical leads202run. In other embodiments, the electrical leads202are cast within the material that makes up the elongated shaft.

As illustrated inFIG. 1, flexible multi-conductor cable112(and more particularly its constituent electrical leads202) couple to the connector114. Connector114couples the controller104, and more particularly the wand connector120.FIG. 3shows both a cross-sectional view (right) and an end elevation view (left) of connector114in accordance with at least some embodiments. In particular, connector114comprises a tab300. Tab300works in conjunction with a slot on wand connector120(shown inFIG. 4) to ensure that the connector114and wand connector120only couple in one relative orientation. The illustrative connector114further comprises a plurality of electrical pins302protruding from connector114. Each electrical pin302is coupled to a single electrical lead in the leads202. WhileFIG. 3shows only four illustrative electrical pins, in some embodiments26or more electrical pins may be present in the connector114.

FIG. 4shows both a cross-sectional view (right) and an end elevation view (left) of wand connector120in accordance with at least some embodiments. In particular, wand connector120comprises a slot400. Slot400works in conjunction with a tab300on connector114(shown inFIG. 3) to ensure that the connector114and wand connector120only couple in one orientation. The illustrative wand connector120further comprises a plurality of electrical pins402residing within respective holes of wand connector120. At least some of the electrical pins402are each individually coupled to a voltage generator (discussed more thoroughly below) within the controller104. When connector114and wand connector120are coupled, each electrical pin402couples to a single electrical pin302. WhileFIG. 4shows only four illustrative electrical pins, in some embodiments26or more electrical pins may be present in the wand connector120.

FIG. 5shows an electrical block diagram of controller104in accordance with at least some embodiments. In particular, the controller104comprises a processor500. The processor500may be a microcontroller, and therefore the microcontroller may be integral with read-only memory (ROM)502, random access memory (RAM)504, digital-to-analog converter (D/A)506, digital outputs (D/O)508and digital inputs (D/I)510. The processor500may further provide one or more externally available peripheral busses, such as a serial bus (e.g., I2C), parallel bus, or other bus and corresponding communication mode. The processor500may further be integral with communication logic512to enable the processor500to communicate with external devices, as well as internal devices, such as display device124. Although in some embodiments the processor500may be implemented in the form of a microcontroller, in yet other embodiments the processor500may be implemented as a standalone central processing unit in combination with individual RAM, ROM, communication, D/A, D/O and D/I devices, as well as communication hardware for communication to peripheral components.

ROM502stores instructions executable by the processor500. In particular, the ROM502may comprise a software program that implements the various embodiments of adjusting and/or modifying the waveform of the RF energy created by the voltage generator516. The RAM504may be the working memory for the processor500, where data may be temporarily stored and from which instructions may be executed. Processor500couples to other devices within the controller104by way of the digital-to-analog converter506(e.g., in some embodiment the RF generator516), digital outputs508(e.g., in some embodiment the RF generator516), digital inputs510(e.g., interface devices such as push button switches126or foot pedal assembly130(FIG.1)), communication device512(e.g., display device124), and other peripheral devices.

Voltage generator516generates an alternating current (AC) voltage signal that is applied to electrical pins in the wand connector120and ultimately to electrodes of the wand102. In some embodiments, the voltage generator defines an active terminal524and return terminal526. Additional active terminals and/or return terminals may be equivalently used. Each of the terminals524and526couple to electrical pins in the wand connector120. The active terminal524is the terminal upon which the voltages and electrical currents are induced by the voltage generator516, and the return terminal526provides a return path for electrical currents. It would be possible for the return terminal526to provide a common or ground being the same as the common or ground within the balance of the controller104(e.g., the common532used on push-buttons126), but in other embodiments the voltage generator516may be electrically “floated” from the balance of the controller104, and thus the return terminal526, when measured with respect to the common or earth ground (e.g., common532) may show a voltage; however, an electrically floated voltage generator516and thus the potential for voltage readings on the return terminals528,530relative to earth ground does not negate the return terminal status of the terminal526relative to the active terminal524.

The AC voltage signal generated and applied between an active terminal and return terminal by the voltage generator516is RF energy that, in some embodiments, has a frequency of between about 5 kilo-Hertz (kHz) and 20 Mega-Hertz (MHz), in some cases being between about 30 kHz and 2.5 MHz, in other cases being between about 50 kHz and 500 kHz, often less than 350 kHz, and often between about 100 kHz and 200 kHz. In some applications, a frequency of about 100 kHz is useful because target tissue impedance is much greater at 100 kHz. In other applications, such as procedures in or around the heart or head and neck, higher frequencies may be desirable (e.g., 400-600 kHz) to reduce low frequency current flow into the heart or the nerves of the head and neck.

The RMS (root mean square) voltage generated by the voltage generator516may be in the range from about 5 Volts (V) to 1800 V, in some cases in the range from about 10 V to 500 V, often between about 10 V to 400 V depending on the active electrode size, the operating frequency and the operation mode of the particular procedure or desired effect on the tissue (i.e., contraction, coagulation, cutting or ablation). The peak-to-peak voltage generated by the voltage generator516for ablation in some embodiments is a square waveform with a peak-to-peak voltage in the range of 10 V to 2000 V and in some cases in the range of 100 V to 1800 V and in other cases in the range of about 28 V to 1200 V, often in the range of about 100 V to 320V peak-to-peak (again, depending on the electrode size, number of electrodes the operating frequency and the operation mode). Lower peak-to-peak voltage is used for tissue coagulation, thermal heating of tissue, or collagen contraction and may be in the range from 50 V to 1500V, in some cases 100 V to 1000 V and in other cases 60 V to 130 V peak-to-peak (again, using a square waveform).

The voltage and current generated by the voltage generator516may be delivered in a series of voltage pulses or AC voltage with a sufficiently high frequency (e.g., on the order of 5 kHz to 20 MHz) such that the voltage is effectively applied continuously (as compared with, e.g., lasers claiming small depths of necrosis, which are pulsed about 10 Hz to 20 Hz). In addition, the duty cycle (i.e., cumulative time in any one-second interval that energy is applied) of a square wave voltage produced by the voltage generator516is on the order of about 50% for some embodiments as compared with pulsed lasers which may have a duty cycle of about 0.0001%. Although square waves are generated and provided in some embodiments, the AC voltage signal is modifiable to include such features as voltage spikes in the leading or trailing edges of each half-cycle, or the AC voltage signal is modifiable to take particular shapes (e.g., sinusoidal, triangular), as discussed more below.

The voltage generator516delivers average power levels ranging from several milliwatts to hundreds of watts per electrode, depending on the voltage applied to the target electrode for the target tissue being treated, and/or the maximum allowed temperature selected for the wand102. The voltage generator516is configured to enable a user to select the voltage level according to the specific requirements of a particular neurosurgical procedure, cardiac surgery, arthroscopic surgery, dermatological procedure, ophthalmic procedures, open surgery, or endoscopic surgery procedure. For cardiac procedures and potentially for neurosurgery, the voltage generator516may have a filter that filters leakage voltages at frequencies below 100 kHz, particularly voltages around 60 kHz. Alternatively, a voltage generator516configured for higher operating frequencies (e.g., 300 kHz to 600 kHz) may be used in certain procedures in which stray low frequency currents may be problematic. A description of various voltage generators516can be found in commonly assigned U.S. Pat. Nos. 6,142,992 and 6,235,020, the complete disclosure of both patents are incorporated herein by reference for all purposes.

In accordance with at least some embodiments, the voltage generated516is configured to limit or interrupt current flow when low resistivity material (e.g., blood, saline or electrically conductive gel) causes a lower impedance path between the return electrode(s) and the active electrode(s). Further still, in some embodiments the voltage generator516is configured by the user to be a constant current source (i.e., the output voltage changes as function of the impedance encountered at the wand102).

In some embodiments, the various operational modes of the voltage generator516may be controlled by the processor500by way of digital-to-analog converter506. For example, the processor500may control the output voltages by providing one or more variable voltages to the voltage generator516, where the voltages provided by the digital-to-analog converter506are proportional to the voltages to be generated by the voltage generator516. In other embodiments, the processor500may communicate with the voltage generator by way of one or more digital output signals from the digital output508, or by way of packet based communications using the communication device512(the communication-based embodiments not specifically shown so as not to unduly complicateFIG. 5).

FIG. 6shows at least some of the internal components of the voltage generator516in accordance with at least some embodiments. In particular, the voltage generator516comprises a main transformer600. The main transformer600defines a primary winding602and a secondary winding604. The secondary winding604has plurality of leads or terminals that couple to electrical pins of the wand connector120(FIG. 1). In the illustrative case ofFIG. 6, the secondary winding has an active terminal608that couples to the active electrode(s) (by way of a control transformer610(discussed more below)), and return terminal612. The primary winding602comprises a plurality of terminals as well as an electrical center tap (hereafter just center tap). In the illustrative case ofFIG. 6, the primary winding602comprises terminals616and618, and center tap614. Each terminal616and618defines a respective number of turns relative to the center tap608. In some embodiments, the number of turns defined by terminals616and618relative to the center tap608is approximately the same (i.e., within few turns).

Each terminal616and618is coupled to an electrically controlled switch, with the electrically controlled switches illustrated as a field effect transistors (FETs)620and622, respectively. In particular embodiments, the FETs620and622are each a part number IRF540 N-Channel FET available from SGS-Thomson of Phoenix, Ariz. Though FETs are illustrated, other electrically controlled switch devices (e.g., bipolar junction transistors) may be equivalently used. The center tap614is coupled to an alternating current (AC) to direct current (DC) (AC-to-DC) conversion circuit624. The AC-to-DC conversion circuit624takes as input AC signals (e.g., 120 V AC signal from a wall socket), and creates a fixed or selectable DC voltage that couples to the center tap614. The voltage generator516in accordance with the various embodiments induces the RF energy on the secondary winding604by alternately forcing current from the DC signal at the center tap614through a portion of the primary winding in a first direction, and then forcing current from the DC signal through a portion of the primary winding in a second direction. Alternately forcing the current from the DC signal through the primary winding creates an AC signal applied to the primary winding602, which AC signal induces voltages on the secondary winding604.

Consider, as an explanation of using a DC signal coupled to the center tap614yet producing an AC primary winding signal, a positive DC signal applied at the center tap614. Initially, for this example, FET620is made conductive drain-to-source while FET622is non-conductive. Because the source of FET620is coupled to ground, a current flow is induced in the portion of the primary winding602between the center tap614and the terminal616. At a certain time thereafter, as a function of the desired frequency of the RF energy, FET620is made non-conductive and a short time later FET622is made conductive drain-to-source. The process repeats with electrical current from the AC-to-DC conversion circuit624alternately flowing first one direction in the primary winding602, and then the other direction, thus creating an AC signal in the primary of the main transformer600. The AC signal induced on the primary winding602by operation of the FETs620and622induces an AC voltage on the secondary winding604, and thus AC voltages on the active terminal608relative to the return terminal612. The magnitude of the voltage induced is a function of at least the magnitude of the DC voltage applied at the center tap614and the turn's ratio of the main transformer600.

FIG. 6also illustrates a driving circuit for the FETs620and622. In particular,FIG. 6shows a FET driver circuit630coupled to FETs620and622. The FET driver circuit630may be a part number TC4427 available from Microchip of Chandler, Ariz. Other integrated driver circuits, and driver circuits constructed from discrete components, may be equivalently used. The clock signal (CLK) provided to the driver circuits630may be generated within the voltage generator516, or may be provided from an external source, such as the processor500. The frequency and duty cycle of the clock signal may be selected based on the particular procedure that the controller104is used to perform, with the selection based on user interaction with an interface device such as the buttons on the front panel of the controller104, or the pedal system130.

As illustrated, the “A” input of FET driver circuit630follows the clock signal. As the clock signal oscillates between a high voltage and a low voltage, the gate of FET620is driven high by the FET driver circuit630with each high voltage state of the clock, and low with each low voltage state of the clock. The illustrative FETs620and622are N-Channel FETs, and are thus conductive drain-to-source when a high gate voltage is present. Thus, during periods of time when FET620has a high gate voltage, FET620is conductive drain-to-source. Likewise, the “B” input of the FET driver circuit630follows a logical NOT of the clock signal (because the clock signal applied to FET driver630first passes through NOT gate632), and the gate of FET622is driven high with each low voltage state of the clock signal. In this case then, the current from the DC signal alternately flows from the center tap614through the FET620and622, and a first AC voltage signal is induced on the terminals of the secondary winding604.

Still referring toFIG. 6, as an additional mechanism to implement voltage control of the AC signal applied to the active and return electrodes, a control transformer610is electrically coupled to the main transformer604. The control transformer is implemented as a selectable impedance device. In particular, when a lower voltage AC signal is desired on the active electrode(s) relative to the return electrode(s), the impedance the AC signal experiences across the control transformer is increased and thus the AC signal experiences a higher voltage drop resulting in less voltage applied to the electrodes of the wand. Likewise, when a higher voltage AC signal is desired on the active electrode(s) relative to the return electrode(s), the impedance the AC signal experiences across the control transformer is decreased and thus the AC signal experiences a lower voltage drop resulting in more voltage applied to the electrodes of the wand. In some embodiments, the selective control of the impedance may be completely within a half-cycle of the AC signal. Stated otherwise, in particular embodiments the impedance changes experienced by the AC signal through the control transformer610may be applied and rescinded within a half-cycle (half a period of the frequency of the AC signal). Application and rescission of impedance changes within a single half-cycle are significantly faster than changes that may be implemented by way of, for example, changing the DC voltage applied to the center tap614of the main transformer600. Selective control of the impedance experienced by the AC signal may take many forms, and each will be discussed in turn, starting with on-off control of electrically controlled switches coupled to a winding of the control transformer.

Control transformer610comprises a first winding640and a second winding642. As illustrated, and in particular embodiments, the control transformer610is identical to the main transformer600; however, other non-identical transformers may be equivalently used. The second winding642defines two terminals644and647. As illustrated, the second winding642couples in series with the secondary winding604of the main transformer600. The first winding640comprises terminals648and650, along with center tap646. Each terminal648and650defines a respective number of turns relative to the center tap646. In some embodiments, the number of turns defined by terminals648and650relative to the center tap646is approximately the same (i.e., within few turns).

Each terminal648and650is coupled to an electrically controlled switch, the electrically controlled switch for each tap illustrated as FETs652and654, respectively. In particular embodiments, the FETs652and654are part number IRF540 N-channel FETs. Though FETs are illustrated, other electrically controlled switch devices (e.g., bipolar junction transistors) may be equivalently used. The center tap646may be grounded, coupled to a voltage source, or electrically floated. For now, assume the center tap646is electrically floated.FIG. 6also illustrates a control circuit651for driving the FETs648and650. In particular, the control circuit651comprises a FET driver circuit653coupled to FETs648and650. The FET driver circuit653may also be a part number TC4427 discussed above. Other integrated driver circuits, and driver circuits constructed from discrete components, may be equivalently used. The “A” and “B” inputs of FET driver circuit653are driven by impedance control circuit655. Thus, in the particular embodiments, under control of the impedance control circuit655, the FETs652and654are driven between an off-state and a fully-conductive (i.e., saturated) state based on the state of the control inputs to the FET driver circuit653.

In order to describe embodiments where the FETs652and654are used as on-off devices, consider first a situation where both FETs652and654are non-conductive. In the state where FETs652and654are non-conductive, no electrical current flows in the first winding640and the impedance exhibited by the second winding642of the control transformer is at a high or maximum value. Thus, the AC voltage signal from the main transformer600(which voltage signal may be referred to as an intermediate AC voltage signal) propagates through the second winding642of the control transformer610and experiences a voltage drop based on the impedance of the second winding642. The intermediate AC voltage signal, after experiencing the voltage drop across the second winding642, may be referred to as the final AC voltage signal, as it is such signal that is applied to the pins of the connector120and ultimately the electrodes of the electrosurgical wand102.

Now consider the situation where the FETs652and654are fully conductive, and thus electrical current is free to flow in the first winding640of the control transformer. In such an illustrative situation, electrical current flow in the second winding642induces voltage and current in the first winding640. In particular, during a first or positive half-cycle of the AC voltage signal (and considering the center tap646electrically floated), the electrical current flow in the second winding642induces a voltage and electrical current in the first winding640proportional to the turns ratio of the transformer. The electrical current in the first half-cycle may flow through the shorting diode656, through the first winding640, and then through the FET652to ground or common. During a second or negative half-cycle of the AC voltage signal, the electrical current flow in the second winding642again induces a voltage and electrical current in the first winding640proportional to the turns ratio of the transformer, but with opposite polarity. The electrical current in the second half-cycle may flow through the shorting diode658, through the first winding640, and then through the FET654to ground or common. Thus, during each half-cycle the first winding640is effectively electrically shorted at its terminals648and650. During each half-cycle, the electrical current induced in the first winding640lowers the impedance exhibited by the second winding642. Thus, in propagating from the main transformer600through the second winding642of the control transformer610, the AC voltage signal generated by the main transformer600experiences its lowest voltage drop across the second winding642(thereby creating the final AC voltage signal) before being applied to the active electrode.

The various embodiments discussed to this point have assumed that the FETs652and654are either non-conductive for extended periods of time (at least a half-cycle of the AC voltage signal), or conductive for extended periods of time. Operating the FETs in such a manner provides a two-state control of the final AC voltage signal applied to the active electrode(s) relative to the return electrode(s). However, in other embodiments the FETs652and654associated with the first winding640may be made conductive and then non-conductive within a half-cycle, and in some cases multiple times within a half-cycle. Consider first a situation where the physician using the electrosurgical controller desires to apply a waveform to the electrodes of the electrosurgical wand102that has a leading-edge spike.

FIG. 7shows a plurality of waveforms, each plotted on a different ordinate axis, but with corresponding time. In particular, plot700shows a plurality of possible AC voltage signals applied to the electrodes of a wand, plot702shows gate voltage for FET652assuming a N-channel FET, and plot704shows a gate voltage for FET654assuming a N-channel FET. Time period706illustrates the waveform having leading edge spikes, along with the gate voltages for FETs652and654to achieve the spikes. In particular, during the positive half-cycle gate voltage pulse708makes illustrative FET652conductive, and thus the impedance across the second winding642of control transformer610low. In such a situation, the voltage drop across the second winding642is low, and thus initially the voltage applied to the active electrode(s) relative to the return electrode(s) is relatively high. However, after the leading edge spike, but still within the half-cycle, the gate voltage drops to zero, and thus FET652becomes non-conductive. A non-conductive FET652results in higher impedance exhibited by the second winding642of the control transformer, a larger voltage drop across the second winding642, and thus the AC voltage signal applied to the electrodes drops.

Still referring toFIG. 7, in the immediately subsequent (i.e., negative) half-cycle, the gate voltage for FET652remains zero, the gate voltage pulse710makes illustrative FET654conductive, and thus the impedance across the second winding642of control transformer610again becomes low. The voltage drop across the second winding642is low, and thus initially the voltage applied to the active electrode(s) relative to the return electrode(s) is a relatively large negative value. However, after the leading edge spike, but still within the second half-cycle, the gate voltage for FET654drops to zero, and thus FET654becomes non-conductive. A non-conductive FET654results in higher impedance exhibited by the second winding642of the control transformer, a larger voltage drop across the second winding642, and thus the AC voltage signal applied to the electrodes become less negative. Thereafter, the cycle may repeat as shown.

Now consider a situation where the physician using the electrosurgical controller104desires to apply a waveform to the electrodes of the electrosurgical wand102that has a trailing-edge spike.FIG. 7, particularly the plots in time frame720, show the AC voltage signal with trailing edge spikes, as well as gate voltage for the FETs652and654to achieve the spikes. In particular, during an initial portion of a first half-cycle, the gate voltage for FET652is low and thereafter, but within half-cycle, the gate voltage pulse722makes illustrative FET652conductive. Thus the impedance across the second winding642of control transformer610is initially high, and then transitions to low impedance within the half-cycle, thus creating a voltage spike at the end of the waveform within the half-cycle. During an initial portion of a second or negative half-cycle, the gate voltage for FET652is low and the gate voltage for FET654is also initially low. Thereafter, but within the half-cycle, the gate voltage pulse724makes illustrative FET652conductive. Thus the impedance across the second winding642of control transformer610is initially high, and then transitions to low impedance within the half-cycle, thus creating a voltage spike at the end of the waveform within the negative half-cycle.

Now consider a situation where the physician using the electrosurgical controller104desires to apply a waveform to the electrodes that is more sinusoidal.FIG. 8shows a plurality of waveforms, each plotted on a different ordinate axis, but with corresponding time. In particular, plot800shows a plurality of possible AC voltage signals applied to the electrodes of a wand, plot802shows gate voltage for FET652assuming a N-channel FET, and plot804shows a gate voltage for FET654assuming a N-channel FET. Time period806illustrates a substantially sinusoidal waveform, along with the gate voltage pulses for FETs652and654to achieve the substantially sinusoidal waveform. In particular, the time period806illustrates not only wave-shaping of the AC voltage signal, but also wave shaping by changing the frequency of the pulses applied to the FETs652and654. Assuming a constant duty cycle, during the positive half-cycle, the frequency of the voltage pulses808applied to the gate of FET652are initially relatively low, increase toward the middle of the half-cycle, and decrease toward the end of the half-cycle. Thus, initially the average impedance of the second winding642is high (large voltage drop and thus lower voltage applied to the electrodes), the average impedance increases toward the middle of the half-cycle (lower voltage drop and thus higher voltage applied to the electrodes), and the average impedance decreases toward the end of the half-cycle (large voltage drop and thus lower voltage applied to the electrodes). Likewise for the negative half-cycle in the time period806, the frequency of the voltage pulses810applied to the gate of FET654are initially relatively low, increase toward the middle of the half-cycle, and decrease toward the end of the half-cycle. Thus, initially the average impedance of the second winding642is high (large voltage drop and thus lower voltage applied to the electrodes), the average impedance increases toward the middle of the half-cycle (lower voltage drop and thus higher voltage applied to the electrodes), and the average impedance decreases toward the end of the half-cycle (large voltage drop and thus lower voltage applied to the electrodes).

Now consider a situation where the physician using the electrosurgical controller104desires to apply a waveform to the electrodes that is triangular. Time period820illustrates the waveform having a substantially triangular wave form, along with the gate voltage pulses for FETs652and654to achieve the substantially triangular waveform. In particular, the time period806illustrates not only wave-shaping of the AC voltage signal, but also wave shaping by changing the duty cycle of the pulses applied to the FETs652and654. During the positive half-cycle, the frequency of the voltage pulses822applied to the gate of FET652is constant and the duty cycle is initially very low. The duty cycle increases linearly toward the middle of the half-cycle, and decrease linearly toward the end of the half-cycle. Thus, initially the average impedance of the second winding642is high (large voltage drop and thus lower voltage applied to the electrodes), the impedance increases toward the middle of the half-cycle (lower voltage drop and thus higher voltage applied to the electrodes), and the impedance decreases toward the end of the half-cycle (large voltage drop and thus lower voltage applied to the electrodes). Likewise for the negative half-cycle in the time period820, the frequency of the voltage pulses824applied to the gate of FET654is constant and the duty cycle is initially very low. The duty cycle increases linearly toward the middle of the half-cycle, and decrease linearly toward the end of the half-cycle. Thus, initially the average impedance of the second winding642is high (large voltage drop and thus lower voltage applied to the electrodes), the impedance increases toward the middle of the half-cycle (lower voltage drop and thus higher voltage applied to the electrodes), and the impedance decreases toward the end of the half-cycle (large voltage drop and thus lower voltage applied to the electrodes).

AlthoughFIG. 8illustrates controlling frequency (with constant duty cycle) with respect to a substantially sinusoidal wave-shaping, and controlling duty cycle (with constant frequency) with respect to a substantially triangular wave-shaping, such is only illustrative. Duty cycle could likewise be used in the sinusoidal wave-shaping, and frequency of the pulses could be used in the triangular wave-shaping. Moreover, a combination of controlling both frequency and duty cycle may be implemented. Furthermore, the sinusoidal and triangular are merely illustrative, and any wave shape may be created by selective control of the impedance of the second winding642.

The various embodiments discussed to this point have assumed on-off control (i.e., driving the FETs between non-conductive and saturated states) of the illustrative FETs652and654to control the impedance of the second winding642, and thus the voltage drop and wave-shaping characteristics thereof. However, in other embodiments the FETs may be used in their active regions.FIG. 9illustrates a portion of the voltage generator516including the control transformer610, FETs652and654, along with active driver circuit900. The active driver circuit900comprises a driver circuit902coupled to FET652, and a driver circuit904coupled to FET654. The driver circuits902and904take commands from the control inputs906, which may originate within the voltage generator516, or may originate with the processor500. Although it may be possible to drive the FETs652and654to their active regions in an open-loop sense (i.e., without feedback), in particular embodiments the driver circuits902and904receive feedback by reading a voltage across resistors910and912, respectively, coupled between the FETs652and654, respectively, and ground or common. Other feedback mechanisms may be equivalently used. Thus, rather than using the FETs652and654as on-off devices, the embodiments ofFIG. 9drive the FETs652and654into their active region in respective half-cycles, thus actively controlling the amount of current in the first winding640.

Consider, for example, that the circuit ofFIG. 9is utilized to create the substantially sinusoidal waveform of time period806inFIG. 8. During the initial portion of the positive half-cycle, driver circuit902drives the FET652to be either non-conductive or only slightly conductive. As the positive half-cycle progresses, the driver circuit902drives the FET652to be more conductive, and then in the waning portion of the positive half-cycle the driver circuit902drives the FET652to be either non-conductive or only slightly conductive. The point is, during a portion of the half-cycle, the FET652is utilized in its active region for extended amounts of time, and not as a merely a transition between the non-conductive and saturated states. During the initial portion of the negative half-cycle, driver circuit904drives the FET654to be either non-conductive or only slightly conductive. As the negative half-cycle progresses, the driver circuit904drives the FET654to be more conductive, and then in the waning portion of the negative half-cycle the driver circuit904drives the FET654to be either non-conductive or only slightly conductive. Here again, during a portion of the negative half cycle, the FET654is utilized in its active region for extended amounts of time, and not as a merely a transition between the non-conductive and saturated states.

In order to more fully define the active region as opposed to saturation, attention is now directed toFIG. 10. In particular,FIG. 10shows a transistor curve for the illustrative IRF540 N-Channel FET. The abscissa axis is the voltage drain-to-source (VDS), the ordinate axis is the current through the drain (ID), and the multiple curves within the plot are based on varying gate-to-source voltage (VGS). As shown inFIG. 10, in transitions between lower gate-to-source voltage VGSto higher gate-to-source voltage VGS, at lower voltage levels changes result in significant changes in drain current ID. For example, a change in gate-to-source voltage VGSfrom 5 V (curve1000) to 6 V (curve1002) results in more than doubling of the gate current IDfrom about 15 amps to about 37 amps. However, as the drain current IDincreases, the effect of increasing gate-to-source voltage VGShas less effect on drain current ID. For example, a change in gate-to-source voltage VGSbetween 8 V (curve1004) and 10 V (curve1006) results in an increase in gate current of only a few amps. In some transistors, beyond a particular gate-to-source voltage VGS, increase have no effect on drain current ID. When changes in gate-to-source voltage result in no appreciable changes in drain current, the transistor is said to be saturated. Thus, for purposes of this disclosure and the claims, when a transistor is said to be operating in the active region, the transistor is operated within a region where changes in gate-to-source voltage (or base current for junction transistors) has an appreciable effect on drain current (emitter current for junction transistors). Temporary or fleeting presence in the active region while transitioning between a non-conductive state and a saturated stated for on-off control shall not be considered operation within the active region.

Stated otherwise, with respect to on-off control versus active region control, operation of the FETs in the active region is distinguished from operation of the FETs in the saturated region by virtue of the means used to control and regulate the average current through the FET. In the case of active control, the system makes use of the linear region of operation of the FET, whereby the slope of the ratio of the drain current to the drain to source voltage (ID/VDS) is determined by value of the gate to source voltage, VGS. In this operating mode, either the average value of the current delivered through the FET or the profile of the current waveform delivered through the FET can be regulated by a variation in VGS, provided that the gate to source voltage is maintained below the point where the drain current becomes mostly constant, or independent of the drain to source voltage. When the FETs are operated in the saturated region, the drain current is for the most part independent of the drain to source voltage, and the FET operates as a type of electrical switch. In this mode of operation, the average current delivered through the FET, or the profile of the current waveform delivered through the FET, is regulated by an adjustment or variation in the time where the FET is either saturated or non-conductive. Those skilled in the art will appreciate that during the transition between the non-conductive state and the saturated state, that the FET will by necessity pass through the active region of operation. However, this period of time where the FET is in this mode is not intended to provide a regulation of the delivered current.

The various embodiments discussed to this point have assumed that the main transformer600and the control transformer610are coupled in series. However, other coupling arrangements are possible.FIG. 11shows the main transformer600coupled in parallel with the control transformer610. The arrangement ofFIG. 11may likewise implement wave-shaping of the AC voltage signal applied to the active electrode(s) relative to the return electrode(s). In particular, the main transformer610has finite power transfer capabilities such that changes in impedance of the second winding642may result in increased current flow and thus decreased voltage across the terminals608,612. Thus, in the illustrated embodiments wave-shaping takes place by changing the AC current flow through the second winding642, with decreased impedance resulting in increased current flow through the second winding642. Increased current flow in combination with the current supplied to the electrodes may result in decreased voltage on the secondary winding604. The opposite is also true, with decreased impedance on the second winding642resulting in lower current flow from the secondary winding604and thus increased voltage.

Moreover, the various embodiments described to this point have assumed that the center tap646of the control transformer is electrically opened or floated. However, the center tap need not be floated. For example,FIG. 12illustrates the control transformer610with the center tap646of the first winding640coupled to ground or common. In such a situation, the shorting diodes656and658(FIG. 6) may be omitted, and/or transistors without internal shorting diodes may be used.FIG. 13illustrates the situation where the center tap646is coupled to a DC voltage (e.g., one or two volts). In the embodiments ofFIG. 13, electrical current in the first winding640is not only that induced by the second winding642, but also as flows from the DC voltage source when the FETs652and654(not shown inFIG. 12) are conductive, with greater current flow in the first winding640the impedance of the second winding is further reduced.

The various embodiments discussed to this point have assumed a fixed voltage DC signal at the center tap614of the main transformer600(FIG. 6). Thus, in spite of the fixed voltage DC signal at the center tap614on the primary winding602, multiple output voltages on the active electrode(s) of the wand102may be achieved by control of the impedance of the control transformer610. Having a fixed voltage DC signal created by the AC-to-DC converter circuit624enables voltage generator516to have a relatively simple (and inexpensive) construction. In yet still further embodiments, the AC-to-DC conversion circuit624creates selectable voltage DC signals to apply to the center tap614, and thus the voltage provided to the active electrode(s) relative the return electrode(s) may be controlled not only by the impedance of the control transformer610, but also the DC voltage applied to the center tap614, thus enabling a broader range of control for the output voltages. The selectable DC voltage created by the AC-to-DC conversion circuit624could be created at the command of the processor500(such as commands sent by way of an analog signal from the D/A port506, or one or more digital signals from the D/O port508, or both) or by a circuit within voltage generator516(not shown so as not to unduly complicate the figure).

FIG. 14illustrates a method in accordance with at least some embodiments. In particular, the method starts (block1400) and proceeds to generating an AC voltage signal within an electrosurgical controller (block1404). In some embodiments, the generating comprises inducing an intermediate AC voltage signal on a secondary winding of a first transformer (block1408), and wave shaping the intermediate AC voltage signal by a second winding of a second transformer coupled to the first transformer (and thereby creating the final AC voltage signal) (block1412). Thereafter, the illustrative method involves applying the final AC voltage signal to electrical pins of a connector configured to couple to an electrosurgical wand (block1416), and the illustrative method ends (block1420).

While preferred embodiments of this disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching herein. The embodiments described herein are exemplary only and are not limiting. For example, the various FETs associated with of the control circuit680are illustrated as N-Channel FETs; however, P-Channel FETs, bipolar junction transistors and in some cases solid state relays may be equivalently used. Moreover, while the wave-shaping described has been as applied equally to both the positive half-cycle and negative half-cycle of the AC voltage signal, in other embodiments the wave-shaping may be applied in different magnitudes as between the positive half-cycle and negative half-cycle, and thus the final AC voltage signal applied to the electrodes of the electrosurgical wand may have a DC bias. Because many varying and different embodiments may be made within the scope of the present inventive concept, including equivalent structures, materials, or methods hereafter though of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.