MXPA99001804A - Improved electrosurgical generator - Google Patents

Abstract

An electrosurgical generator is disclosed that provides radio frequency electrical waveforms for performing surgical operations on a tissue mass. The various aspects of the present invention are embodied in an electrosurgical generator that includes a DC regulator (10), an amplifier (100), an energy recovery circuit (90), and a method of controlling these components to generate a desired electrical waveform for an electrosurgical operation.

Description

IMPROVED ELECTROCHIRGER GENERATOR FIELD OF THE INVENTION This invention relates to electrosurgical generators in general, and in particular, to an improved electrosurgical generator capable of supplying a plurality of electrical radio frequency waveforms for surgical procedures.

BACKGROUND Electrosurgery involves the application of radio frequency electrical energy to the tissue to produce a surgical operation. Electrosurgery is usually performed with a generator that converts electrical energy from a power source to a predetermined radio-frequency waveform that is delivered to the tissue through an active electrode and a return path. Essentially there are four major surgical operations that are electrically performed on tissues, depending on the output of the radio frequency waveform by the generator. These operations are typically described as desiccation, fulguration, cutting and cutting with hemostasis. For a drying operation, the generator produces a radio-frequency waveform that heats the tissue, through electrical resistance heating due to the current flowing through the tissue, sufficient to produce an area of necrosis. For a fulguration operation, the generator typically produces an explosive waveform, which has a high peak voltage but a low utilization cycle. Due to the low utilization cycle of the fulguration waveform, the energy per unit time applied to the tissue is low enough so that the explosive vaporization of the cell's moisture is minimized. The explosive waveform forms a radio-frequency spark or arc between the active electrode and the tissue, thus supplying energy over the spark contact area or arc of the tissue and providing coagulation of the tissue very close to the spark or arc. Other operations can be performed with different waveform outputs through an electrosurgical generator. The cut occurs when enough energy per unit of time is supplied to the tissue to vaporize the moisture in the cell. The cut is typically performed with a repetitive voltage waveform, such as a sinusoid, which produces a cut with very little necrosis and low hemostasis. It is also possible to achieve a combination of the above operations by varying the electrical waveform produced by the generator. In particular, a combination of cutting and desiccation (called haemostasis or blending) can be produced by interrupting p-eriodically the continuous sinusoidal voltage normally used to produce an electrosurgical cut.

Known electrical generators, which are capable of producing one or more of the operations described above, are generally designed as shown in Figure 1. The AC (alternating current) force conductors 200 provide the AC electrical power to the converter of AC / DC 202, which provides unregulated DC (direct current) energy to the controller DC 206. Under the control of the physician 208, the control and time circuit 210 causes the DC 206 controller to produce energy of a value specific to the tuned RF (radio-frequency) amplifier 212. The control and time circuit 210 also produces RF signals for amplification through the tuned RF amplifier 212. This results in the RF energy signals being supplied to the patient 214. Known electrosurgical generators are subject to one or more limitations. For example, some generators are limited in the degree to which they can generate more than one individual waveform without producing a mixture of inappropriate effects, so they are limited in the number of waveforms that are appropriate for surgical operations. Another limitation is that known generators emit a substantial amount of electromagnetic interference to the environment. Electromagnetic interference has a serious risk in the operating rooms, where they can cause malfunction or failure of electronic equipment. A primary source of electromagnetic interference are the substantial pulsating currents that are created in the electrosurgical generated circuits. Mainly there are two sources of electromagnetic interference (EMI) in known generators. Said EMI consists of conducted EMI, near-field EMI and radiated EMI. A main source of conducted EMI, which is sent to the AC power lines and carried to the equipment at distant sites in the hospital and more, is produced by substantially pulsating currents, which are created in the DC 206 controller. A principal source of near-field EMI and radiated EMI is the harmonic content of the output of the tuned amplifier. The harmonic components are much better suited to the environment, and are radiated more effectively. As will be shown, a key aspect of this invention is the simultaneous reduction of the conducted, near-field and radiated EMI. Another limitation of known electrosurgical generators is their relatively low efficiency to convert and amplify the electrical energy from the energy source to the tissue, resulting in the dissipation of electrical energy as heat. The dissipation of heat through an electrosurgical unit (ESU) inside an operating room is inconvenient due to the generation of convective air currents and the associated circulation of pathogens carried by the air. The additional heat dissipation requirement increases the weight and volume of the ESU. In addition, the safety of the surgical unit typically decreases as the heat dissipation increases. The low efficiency in the ESUs is caused by a number of effects: (1) The selected topology, which determines the intrinsic efficiency (maximum efficiency of obtaining under optimal conditions); (2) The load, which determines the intrinsic efficiency (efficiency obtained with the given topology in a given load); (3) The component selection, which determines the efficiency achieved (efficiency of a given topology, load and selection of components). Ideally, a topology is selected that maximizes extrinsic efficiency and performed over a wide range of conditions. In known ESUs, in order to achieve a cut with a minimum of hemostasis, the AC ripple voltage present at the output of the DC regulator must be minimized. At the same time, the conducted EMI should be the most possibly reduced. To do this, large-sized capacitors are sometimes added to the AC / DC converter 202, in Figure 1, in an attempt to smooth the current pulses, reducing the conducted EMI, while at the same time adding large capacitors to the capacitor. the DC regulator output 206 to reduce the output ripple and, therefore, reduce haemostasis. These capacitors filter the current by passing the ripple component to ground through the ESR of the capacitor, thus wasting energy. This loss and volume could be greatly reduced if less AC ripple were generated, and therefore less wasted energy. Control devices, such as transistors, are usually used in both the DC regulator 206 and the RF amplifier circuits 212 to synthesize and regulate the electrical waveform applied to the tissue. These control devices can be used in a variety of ways. A very common method in the prior art has been used for the control devices as variable impedance current sources, which result in the simultaneous application of voltage and current through the transistor and in this way a dissipation of the energy within the transistor. The control devices are also used as low impedance (ie closed) and high impedance (ie open) alternating switches. In the prior art, some generator circuits dissipate a substantial amount of energy in said switches due to the transition of the switches to low impedance while a voltage exists through the switch and thus dissipating the power due to the simultaneous presence of voltage and current in the switch. Some pathologies of generator circuits containing transistors usually can not link the derivation of the transistors to a common reference node, thus requiring a relatively complicated level circuit system.

Some topologies of known electrochemical generators convert the input voltage to an output voltage through a method that includes storing the input energy inductively in the form of a DC magnetic field during an interval and releasing the energy as a oscillation through a load during a subsequent interval. This energy storage and release procedure results in a waveform in the form of a damped sinusoidal, which has a significant amplitude remaining at the time of the next storage cycle. For some output waveforms, such as pulsed energy waveforms, energy not sent to the load across the pulse end remains in the generator, where it dissipates as heat, reducing generator efficiency. Consequently, there is a need for a generator that directs said limitations of known electrosurgical generators.

COMPENDIUM OF THE INVENTION Accordingly, the objects of the present invention include the following: Providing an electrosurgical generator with reduced generation of electromagnetic interference. - Provide an electrosurgical generator with improved efficiency. Provide an electrosurgical generator with current isolation between an input power source and an output load. Provide an electrosurgical generator with a reduced number and size of electrical components. Provide an interrupting DC regulator for an electrosurgical generator, wherein the ripple of input and output current is substantially reduced. Provide an interrupting DC regulator for an electrosurgical generator with an adjustable output DC voltage that can be increased (raised) or reduced (reduced) in relation to the input DC voltage. Provide an amplifier for an electrosurgical generator that converts a DC input voltage to a radio frequency signal that provides surgical effects in the tissue with reduced generation of electromagnetic interference and increased efficiency. Provide an energy recovery circuit for an electrosurgical generator that selectively stores and releases energy within the generator to increase the efficiency of the energy supply to the tissue. Provide an electrosurgical generator by which the energy flow to the tissue is controlled in response to a perceived tissue condition to provide improved surgical effects. One or more of the above objects are addressed by providing a generator comprising a DC regulator of the invention, amplifier, and energy recovery circuit. These generator components can be controlled in an inventive manner to convert the energy of a power source to a predetermined radio-frequency waveform scale to provide electrosurgical operations, for example, desiccation, fulguration, cutting or cutting with hemostasis. The DC regulator and the amplifier are connected in series between a power source (for example, a battery or an AC to DC converter) and the tissue. Generally, the power source provides a DC voltage to the DC regulator. The DC regulator converts the input DC voltage to a scale of DC output voltages that may be greater (elevation) or lower (reduction) than the DC input voltage. The DC output voltage flows to the amplifier, where it is converted to a scale of radio-frequency voltage waveforms, which are supplied to the tissue. The energy recovery circuit stores and releases the energy generated by the amplifier to increase the efficiency with which the energy is transferred from the energy source to the tissue. In accordance with one aspect of the invention, an inventive switched DC regulator is provided which achieves an increased efficiency, a reduced generation of electromagnetic interference, and a reduced number of circuit components. The switched DC regulator converts a first DC signal from a power source to a second DC signal having a predetermined voltage. The switched DC regulator includes input inducer means (eg, one or more inductors) to reduce current ripple in the first DC signal, capacitor means (e.g., one or more capacitors) to store and release, in of capacitor, power, first switching means (for example, a bipolar transistor, diode, bipolar isolated gate transistor, or field effect transistor) for alternately charging the capacitor means with the first DC signal and second switching means for discharging the capacitor means for generating the second DC signal, and output inductor means (e.g., one or more inductors) to reduce current ripple in the second DC signal. The input inductor means are connected in series between the power source and the capacitor means. The capacitor means are connected in series between the input inductor means and the output inducer means. The energy is transferred, in a capacitor manner, from the input inductor means to the output inductor means through the first switching means charging the capacitor means with the first DC signal and the second switching means discharging the means of capacitor through the output inductor means to generate the second DC signal. The voltage of the second DC signal is controlled by adjusting the utilization ratio of the first and second switching means, i.e., adjusting the ratio of the time in which the capacitor means is charged to the total time during which the capacitor means is loaded and downloaded. The voltage of the second DC signal may be higher (elevation) or lower (reduction) than the voltage of the first DC signal. In addition, the current undulations in the first DC signal and the second DC signal are reduced by appropriately coupling the input inducer means and the output inducer means in magnetic form. The appropriate magnetic coupling is achieved by considering the coupling coefficient K and the ratio of N turns of a transformer. In addition, the proper magnetic coupling occurs when K is substantially equal to N for the transformer. Said substantial equivalence may be obtained either by using a transformer designed so that K is substantially equal to N or by using a transformer together with one or more auxiliary inductances, said auxiliary inductances selected so that K is substantially equal to N. The insulation of DC between the first DC signal and the second DC signal is achieved through the capacitor means including a first and second capacitor with an isolation transformer interposed between the capacitors. The current ripples in the first DC signal and the second DC signal are substantially reduced to zero by magnetically coupling the input and output inductor means and the isolation transformer. The efficiency of the DC regulator is substantially improved by selecting the input inductor means, the output inductor means and the capacitor means to provide a substantially zero voltage across the switching means and a substantially zero instantaneous change rate of voltage across the switch means before the switch means close to load the capacitor means. In this way, the dissipation of energy in the switching means is substantially eliminated avoiding the simultaneous application of a voltage through the switching means and a current through the switching means. According to another aspect of the present invention, an inventive amplifier is provided which converts the second DC signal generated by the DC regulator to a radio frequency output signal having a predetermined frequency appropriate for achieving electrosurgical effects. The amplifier of the invention produces increased efficiency and reduced generation of electromagnetic interference. The amplifier includes input inductor means in series with the DC controller or other DC source (for example, an AC to DC converter, or battery), a resonant circuit connected in series with the input inductor means, and switching means in parallel with the resonant circuit. The input inductor means reduces the current ripple in the second DC signal and thus reduces radiated electromagnetic interference. The resonant circuit includes an inductor, a capacitor and the tissue. The switch alternately connects (closed switch) and disconnects (open switch) a junction between the input inductor and the resonant circuit to a current return path for the amplifier, thereby periodically charging the resonant circuit with the second DC signal and discharging power as the output signal. The magnitude and frequency of the output signal is regulated by adjusting the utilization ratio and the switch period, i.e., adjusting the ratio of the time in which the resonant circuit is charged to the total time during which the resonant circuit is charged and Discharged. The components of the resonant circuit are selected to provide a substantially zero voltage and a zero change rate of voltage across the switch prior to closing the switch to charge the input inductor. In this way, the energy dissipation in the switch is substantially eliminated avoiding the simultaneous application of a voltage potential across the switch and a current through the switch, and the sensitivity of the amplifier circuit to the component tolerances is substantially reduced. In accordance with another aspect of the present invention, an energy recovery circuit is provided for use in an electrosurgical generator that improves the energy delivery efficiency to the tissue. An electrosurgical generator synthesizes bursts of varying width / waveforms of radio-frequency energy to create the various types of surgical operations. At the end of a burst type output signal, the energy that had not been delivered to the tissue remains inside the generator, where it dissipates as heat. The energy dissipated within the generator can be quite high when the fabric resistance is relatively high. The energy recovery circuit substantially reduces those losses by recovering the remaining energy within the electrosurgical generator at the end of a burst / waveform. The energy recovery circuit generally includes an energy storage device (s) (e.g., capacitor, inductor, or a combination thereof), a switch (s) (e.g., a bipolar transistor, bipolar gate transistor isolated , or a field effect transistor) that alternatively stores and releases energy between the energy storage device (s) and the electrosurgical generator, and a switch controller that regulates the storage and release of energy. Generally, to reduce the energy loss at the end of a burst output signal, the switch controller switches the switch to alternately store the energy in the energy recovery circuit near the end of a burst and then release the stored energy during the subsequent burst. In this way, the energy can be selectively stored and then released to increase the efficiency of the energy transfer to the tissue. As can be seen, the energy recovery circuit can be controlled to store and release the energy at any time and thus does not limit itself to storing the energy at any time and thus does not limit itself to storing energy at any time particular, such as near the end of a burst output signal. According to another aspect of the present invention, a method for the operation of an electrosurgical unit is provided, whereby the flow of energy to the tissue is controlled in response to a perceived tissue condition to provide improved surgical effects, for example , drying, fulguration or cutting with hemostasis. It has been found that the complex impedance of the tissue provides information regarding the condition of the tissue and in this way the condition of a surgical effect. The complex impedance of the tissue includes a resistance and a capacitance. Generally, the tissue includes cells and fluid. The resistance of the tissue is created through the electric conduction path through the fluid. The capacitance of the tissue is created by the cell membranes that provide an electrical insulating effect around the electrically conducting fluid within the cells. The cell membranes are perforated / burst when a sufficient voltage is applied through the tissue. After the cell membrane bursts, the capacitance effect of the membrane is substantially reduced and the associated complex impedance of the tissue becomes more resistive and less capacitive. The complex impedance of the tissue is also changed when enough energy is dissipated in the tissue to vaporize some of the fluid thus causing an increase in resistance. Additional changes in complex impedance are created through effects such as denaturation and protein recombination in response to heating. It has also been found that the complex impedance of the tissue can be measured over a period to observe the degree, if any, of cell membrane resealing. For example, cells that have not been destroyed by electrosurgical energy can reseal small holes in the cell membrane for a period of about one millisecond to one second. The measurement of. change and the rate of change of the complex impedance of the tissue between or during the delivery of the electrosurgical energy provides the information with respect to the condition of the tissue and the desired surgical effect. The method of the present invention for operating an electrosurgical unit includes controlling the delivery of energy to the tissue in response to the perceived complex impedance of the tissue and / or rate of change of the complex impedance to provide improved surgical effects. More particularly, a sensor, which uses an impedance controller for use with an electrosurgical generator to sense the complex impedance of the tissue, is included in the present invention, wherein the impedance controller regulates the output, for example, the voltage that is converted to an RF signal, from the generator circuit in response to the change in the measured complex impedance of the tissue.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complex understanding of the present invention and other advantages thereof, reference is now made to the following Detailed Description, taken in conjunction with the accompanying drawings, in which: Figure 1 is a prior art embodiment of a generator electrosurgical Figure 2 is a flow diagram illustrating the components of the generator; Figure 3 is a schematic view of one embodiment of the DC controller according to the present invention; Figure 4 is a schematic view of one embodiment of the isolated DC controller according to the present invention; Figure 5 is a schematic view of one embodiment of the amplifier according to the present invention; Figure 6 is a schematic view of one embodiment of an energy recovery circuit; Figure 7 is a schematic view of an energy recovery circuit embodiment in combination with the amplifier of Figure 5 according to the present invention; Figure 8a is a complex impedance model of tissue distributed from a tissue sample; Figure 8b is a sample of a tissue structure; and Figure 9 is a block diagram of a tissue impedance controller in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 2, a block diagram of an electrosurgical generator constructed in accordance with the principles of the present invention is shown. The electrosurgical generator includes a DC regulator 10, an amplifier 100, an energy recovery circuit 90 and a controller 70. The regulator DC 10 receives an input DC voltage from an energy source 12 and converts the input DC voltage to a DC output voltage that is provided to the amplifier 100. The amplifier 100 converts the DC voltage of the regulator 10 to a radio-frequency output signal that is provided to a mass of tissue 11. The energy recovery circuit 90 alternately stores energy of the amplifier 100 and releases energy back to the amplifier 100 to increase the efficiency at which the energy is transferred from the energy source 12 to the tissue. The controller 70 regulates the DC regulator 10, the amplifier 100 and the energy recovery circuit 90 to create a radio frequency output signal of the electrosurgical generator that is operative to perform a desired electrosurgical operation, eg, desiccation, Fulguration, cutting or cutting with hemostasis. The DC 10 regulator of the invention was first described. This description is followed by a description of the amplifier 100 of the invention and then the energy recovery circuit 90 of the invention. Finally, a tissue impedance controller 109 (FIG. 9) is described that controls the flow of energy to the tissue in response to a perceived tissue condition to provide improved surgical effects. In one aspect of the invention, the DC controller 10 (FIG. 3) converts an input DC voltage from the power source 12 to an output DC voltage that may be higher or lower than the first DC voltage. The DC 10 regulator accomplishes this conversion with superior efficiency, substantially reduced electromagnetic interference radiation, and a smaller number and smaller component size than known electrosurgical generators. The DC controller 10 includes an input inductor 16 in series with the DC power source 12, an output inductor 18 in series with the amplifier circuit 100, and an energy transfer circuit 20. The energy transfer circuit 20 it includes a storage capacitor 24, a switch 26 (for example, a bipolar transistor of isolated gate) to alternately connect (i.e., a closed switch) and disconnect (i.e., an open switch) a first junction 28 between the inductor of input 16 and storage capacitor 24 to a current return path 30 of the power source 12, and a diode 32 for alternately connecting (i.e., diverted bypass diode) and disconnecting (i.e., diverted reverse diode) a second junction 34 between the storage capacitor 24 and the output inductor 18 to the current return path 30. A filter capacitor 36 is connected through the output of the DC controller 10. During the interval when the switch 26 is opened, the diode 32 is deflected forward and the capacitor 24 is charging through the input inductor 16, which reduces the ripple of input current and radiated electromagnetic interference. During the interval when the switch 26 closes, the capacitor 24 is connected through the diode 32, thus reversely diverting the diode 32. The capacitor 24 discharges through the output inductor 18 and the amplifier 100. The output inductor 18 reduces the ripple of output current and radiated electromagnetic interference. The switching cycle is then repeated by the switch 26 opening to the forward branch of the diode 32 and to recharge the capacitor 24 through the input inductor 16. In this way, the DC 10 regulator, by means of training, transfers energy from the source of energy 12 to amplifier 100. The capacitance energy transfer is substantially more effective on a basis of size and weight per unit than the inductive energy transfer used in previous electrosurgical generators. For example, a capacitor of 1 microfarad charged at 50 V has a stored energy of 1.25 mJ, equal to an inductor of 2.5 mH passing 1A. The capacitor size of 50 V of 1 microfarad, however, is considerable smaller than an inductor of 2.5 mH 1A. In addition, the training energy transfer is more efficient than the inductive energy transfer, which has a relatively high loss of energy transferred due to resistive heating of the inductor. The DC output voltage of the DC regulator 10 may be higher or lower than the DC input voltage of the power source 12 and is adjusted according to the following formula: V output / V input = D / D 'where : V output is the DC output voltage; input V is the DC input voltage; D is the fractional time that the switch 26 remains closed (i.e., the time that the switch 26 s closed divided by the time for a cycle between the switch closing a first time and then a second time); and D 'is the fractional time that the switch remains open (ie, D' = (1-D)). In this way, the output voltage can be adjusted to lower than the input voltage (reduction conversion) for D < 0.5 or above the input voltage (elevation conversion) for D > 0.5 The controller 70 adjusts the output voltage by opening the switch 26 (i.e., bypassing the transistor to achieve a low impedance) and closing the switch 26 (i.e., bypassing the transistor to achieve a high impedance) according to the above formula. The controller 70 in Figure 3 performs a current feedback control by sensing the output current at the node 38 and adjusting the utilization cycle of the switch 26 to maintain the voltage and / or current of the DC regulator 10 within a predetermined range for provide a desired surgical effect. The energy dissipation in the switch is subtially eliminated by the controller 70 by closing the switch 26 when the subtially zero voltage and the zero voltage change rate are present through the switch 26, thus preventing the simultaneous application of a voltage to the switch. through switch 26 and a current through switch 26. The frequency at which switch 26 can be operated under these zero voltage conditions can be increased by selecting storage capacitor 24 and inductors 16 and 18 to provide a fast discharge of the capacitor 24 through the output inductor 18 and the amplifier 100. In another embodiment, the current ripple in the input inductor 16 and / or the output inductor 18 is further reduced by magnetically collecting the inductors 16 and 18. Magnetic coupling 39 is provided by winding the inductors together on the magnetic core. With the inductors coupled, the energy is transferred to the load through the voltage capacitor 24 (ie, through the electric field) and directly through the coupled inductors 39 (ie, through the magnetic field). The total DC magnetization current in the magnetic core is the sum of the input and output currents. The ratio of turns and the coupling coefficient of the inductors 16 and 18 can be selected so that the current ripple in either, but not both, is reduced to zero. In electrosurgery, it is advantageous to have the DC insulation between an energy source and the tissue / output charge 11. Such isolation is advantageous, for example, due to the subtial variation in tissue strength / output load 11 (eg, varying essentially from zero to infinity). The present invention is easily extended to achieve said isolation. Referring now to Figure 4, a mode is shown that achieves both the isolation between the power source 12 and the amplifier circuit 100 as well as a further reduction of the current ripple in the input and output current ripple. The insulation is provided by dividing the storage capacitor 24 of Figure 3 into two capacitors 40 and 42 and interposing an isolation transformer 44 therebetween. The isolation transformer 44 includes a primary winding 46 and a secondary winding 48. A capacitor 40 is connected in series with the input inductor 16 and the primary winding 46. The other capacitor 42 is connected in series with the output inductor 18 and the secondary winding 48. The inductors 16 and 18 and the isolation transformer 44 can be magnetically coupled 50 to reduce the ripple of input and output currents. Under certain conditions, both the input and output current ripple can be reduced to zero. The input current ripple can be reduced to zero under the following condition: Read = L11 [N2 / N1 - 1] where: Lei is the leakage inductance of the input inductor 16; N1 is the number of turns of the input inductor 16; N2 is the number of turns of the output inductor 18; and L11 is the self-inductance of the input inductor 16. Here, the input ripple current can be reduced to zero having N1 the number of winding turns in the input inductor, substantially equivalent to N2, the number of turns of winding on the output inductor. In one embodiment, N1 and N2 need only be approximately equivalent to produce a reduction in the input current ripple. The ripple of output current can be reduced to zero under the following condition: Le2 = L11 (N2 / N1) 2 [N2 / N1 - 1] where: Le2 is the leakage inductance of the output inductor 18; N1 is the number of turns of the input inductor 16; N2 is the number of turns of the output inductor 18; and L11 is the self-inductance of the input inductor 16. Similarly, the output ripple current can also be reduced to zero having N2 substantially equivalent to N1. Again, in one embodiment, N2 and N1 need only be approximately equal to produce a reduction in the output ripple current. In another aspect of the invention, an improved amplifier 100 is provided to convert the DC output voltage of the DC controller 10 to a radio frequency output signal provided to the fabric 11. The amplifier 100 accomplishes this conversion with high efficiency and a high efficiency. substantially reduced radiation from electromagnetic interference. Referring now to Figure 5, the amplifier 100 includes an input inductor 62 for reducing the input current ripple, a resonant circuit 64 connected in series with the input inductor 62, and a transistor switch 66 for connecting (closing) and disconnecting (opening) alternately a return current path 68 of the amplifier 100 to a junction of the input inductor 62 and the resonant circuit 64. The resonant circuit 64 generally includes an inductor 72, a capacitor 74, and the complex impedance of the tissue impedance 11. The controller 70 adjusts the frequency and magnitude of the radio-frequency output voltage of the amplifier 100 by opening the switch 66 (i.e., bypassing the transistor to obtain a low impedance) and closing the switch 66 (i.e. bypassing the transistor to achieve a high impedance). The controller 70 for the amplifier 100 may include simple oscillation circuits or a more complex feedback controller for regulating the switch 66. Since the switch 66 is cyclically operated by the switch controller 70, the input signal from the DC controller 10 is converted to an output signal corresponding to the switching frequency. The magnitude and frequency of the output signal is regulated by adjusting the utilization ratio of the switch 66, i.e. by adjusting the ratio of the time in which the resonant circuit 64 is charged to the total time during which the resonant circuit 64 is charged and Discharged. During the time in which the switch 66 is closed, the voltage across the switch 66 is essentially zero and the input current flows through the input inductor 62 to ground. The input inductor 62 is sufficiently large in order to act as a substantially constant current source. When the switch 66 is opened, the input current flows through the resonant circuit 64. The transient response of the resonant circuit 64 is the response of a damped second order system created by the series connection of the inductor 72, the capacitor 74 and the tissue impedance 11. The energy within the resonant circuit 64 is dissipated during a passing resonance through the resistive component of the tissue impedance 11. The DC insulation is provided between the amplifier 100 and the tissue impedance 11 through a isolation transformer 76 and DC filter capacitors 78 and 80. 5 The efficiency of the amplifier 100 is improved by selecting the inductor 72 and the capacitor 74 in the resonant circuit 64 to provide a damped response with a voltage of zero and a velocity of -zero. of change of voltage across the switch substantially simultaneously to close the switch 66. The switching "o- of zero voltage in addition to s can be enabled through an anti-parallel diode 67 connected through the switch 66. The antiparallel diode 67 is turned on so that the negative current of switch 66 independent of the switch is opened or closed, and, therefore, more easily and automatically maintain the voltage switching of zero described above. In this way, the power dissipation in the switch 66 is substantially eliminated by preventing the simultaneous application of a voltage across the switch 66 and a current through the switch 66. The zero speed of the voltage change through of switch 66 substantially simultaneous to closure of the switch allows for an increased scale of tissue impedances (ie, a scale of second-order responses) for which a zero voltage commutation will be obtained. According to another aspect of the present invention, the operation condition of the output transformer can be perceived. Said optical perception may be performed using a perception winding 81 which provides a voltage signal 82 to the controller 70. In accordance with another aspect of the present invention, an energy recovery circuit is provided for use in an electrosurgical generator to improve the efficiency of the energy supply to the tissue. The energy recovery circuit generally includes at least one energy storage device (e.g., capacitor, inductor or combination thereof) and at least one switch (e.g., bipolar transistor, bipolar gate transistor isolated, or field effect transistor) that alternately store and release electrical energy in the electrosurgical generator. Referring to Figure 6, there is shown an energy recovery circuit 150 including induction storage means 156, having an inductance L, and capacitor storage means 154, having a capacitance C, wherein both storage means are for storing electric power. In addition, the circuit 150 also includes a substantially DC power supply 152 having a voltage V and a resistive load 158 having a complex impedance Z representing a patient. During an operation, the energy recovery circuit 150 has a state where the first switch 160 is closed and the inductor 156 can charge a stored energy of 1 / 2LI2, where I is the current that passes through the inductor 156.

When the first switch 160 opens the inductor 156 transfers power to the capacitor 154 due to the action of the diode 166. When the diode 166 is conducting, the second switch 162 can be closed. When the second switch 162 is opened, all the energy remaining in the circuit 150 will be stored in the capacitor 154 instead of being dissipated as heat. When another cycle of power supply is started, the voltage, Vc, through the capacitor 154, is measured, and the inductor 156 is charged with current, where: Energy per period = 1 / 2LI2 + 1 / 2CVC2 + í0t I VR2 / Z | dt where: VR is the RMS voltage in the patient 158 t is the period of a power supply cycle. Therefore, the energy that was not dissipated from the circuit 150 and stored in the capacitor 154 is used in the next power supply cycle instead of being dissipated as heat. Referring now to Figure 7, an embodiment of an energy recovery circuit 90 in combination with the amplifier 100 of Figure 5 is shown. The use of an energy recovery circuit 90 in combination with the amplifier 100 of the Figure 5 is only intended to illustrate the operation of the energy recovery circuit 90 and does not limit its use in combination with an amplifier 100. The energy recovery circuit 90 includes a transistor switch 92, an energy storage inductor 96 and a diode 94 in series with the amplifier 100 and in parallel with the energy storage inductor 96. The controller 70 regulates the switch 92 to selectively store and release energy between the energy recovery circuit 90 and the amplifier 100. As previously described , the transient response of the output signal supplied by the amplifier 100 to the tissue impedance 11 for certain op electrosurgical is that of a second-order cushioned system. The energy within the resonant circuit 64 is transferred as a burst to the decaying tissue with a time constant defined by the inductor 72., the capacitor 74 and the impedance of the tissue 11. At the end of a burst of the amplifier 100, the energy that has not been transferred to the tissue 11 generally remains inside the generator where it dissipates as heat. To prevent this loss of energy, the controller 70 stores some of the energy in the amplifier 100 by opening the switch 92 and passing the current through the energy storage inductor 96. At the end of a burst, when the controller 70 opens the switch 66 of the amplifier, the controller closes the switch 92 to trap the energy stored in a closed-loop path by connecting the energy storage jigger 96, the diode 94 and the switch 92. During a subsequent burst (ie, after the controller 70 closes the amplifier switch 66), the controller 70 opens the switch 92, thereby transferring the remaining energy in the energy storage inductor 96 of the amplifier 100. The energy dissipation in the switch 92 is reduced to the minimum by including a diode antiparallel 93 through switch 92. Anti-parallel diode 93 is turned on for negative voltages through the switch 92 to assist in obtaining a zero voltage switching of switch 92. In this way, energy is selectively stored and released between energy recovery circuit 90 and amplifier 100 to increase the efficiency of energy transfer to the tissue. The energy recovery circuit 90 provides the additional advantage of rapidly damping the output energy of the generator at the end of a pulse. With reference to Figures 8a and 8b, the inventors hereby believe that a distributed complex tissue impedance model can be obtained from a tissue structure that is undergoing an electrosurgical procedure. More particularly, the complex impedance 300 of the fabric 400 includes a resistor 310 and a capacitance 320. Generally, the fabric 400 includes cells 404 and 405 and fluid 402. The fabric resistor 310 is created by the path of electrical conduction through the fluid. 402. The tissue capacitance 320 is created by the cell membranes 408, which provide an electrical insulating effect around the electrically conductive fluid 410 within the cells. The cell membranes are perforated / burst, as shown at 406, when sufficient voltage is applied through the tissue 400. After the cell membrane bursts 406, the capacitor effect of the membrane 406 is substantially reduced, as it is shown by the short circuit 330, and the associated complex impedance 300 of the tissue 400 becomes more resistive and less capacitive. The complex impedance 300 of the fabric 400 is further changed when sufficient energy is dissipated in the fabric 400 to vaporize some of the fluid 402 thus causing an increase in the resistance, as shown by the additional resistor 340. Additional changes are created in the complex impedance 300 through effects such as denaturation and recombination of proteins in response to heat. It has also been found that the complex impedance of the tissue can be measured over a period to observe the degree, if any, of cell membrane resealing. For example, cells that have not been destroyed by electrosurgical energy can reseal small holes in the cell membrane for a period of about one millisecond to one second. The measurement of the change and the rate of change of the tissue complex impedance between or during the delivery of electrosurgical energy provides information regarding the condition of the tissue and the associated surgical effect. Referring now to Figure 9, a tissue impedance controller 109 is illustrated for use in an electrosurgical generator in accordance with another aspect of the present invention. The tissue impedance controller 109 includes a generator circuit 110, an impedance measuring device 130, and a controller 120 that responds to the impedance measuring device 130. The generator circuit 110 synthesizes the radio-frequency pulses that are applied through the tissue to produce electrosurgical effects. The impedance measuring device 130 measures the complex impedance of the tissue 11. The controller 120 regulates the generator circuit 100 in response to the measured complex impedance of the tissue 11 and the impedance change rate to provide improved electrosurgical effects. In an embodiment as shown in Figure 9, the tissue impedance 11 is measured between electrosurgical pulses. Between the electrosurgical pulses, the controller 120 regulates the generator circuit 110 to apply a predetermined measurement signal through the tissue 11 for use by the impedance measuring device 130. The impedance measuring device 130 measures the complex impedance of the tissue 11 (i.e., dividing the voltage signal through the tissue between the current through the tissue). The controller 120 analyzes the measured impedance and / or the rate of change of the impedance measured during a predetermined period to determine the present condition of the tissue 11. The controller 120 compares the condition of the present tissue with a desired surgical effect and regulates the generating circuit 110 to obtain the desired surgical effect. In another embodiment, the tissue impedance is measured periodically or continuously during the electrosurgical pulses. The impedance measuring device 130 applies a predetermined frequency voltage through the tissue 11 having a different frequency to the signals synthesized by the generator circuit 110 for electrosurgical purposes. The impedance measuring device 130 measures the current through the tissue 11 at the predetermined frequency to determine the complex impedance of the tissue 11 and thus the fabric condition. The controller 120 then regulates the generator circuit 110 in response to the measured tissue condition to obtain a desired surgical effect. The DC controller 10, the amplifier 100, and the energy recovery circuit 90 of the present invention are each advantageous for use in the generator circuit 110 of the present invention. The controller DC 10 and the amplifier 100 allow the controller 120 to rapidly vary the characteristics of the output signal, including frequency, magnitude and pulse width in response to the measured tissue complex impedance 11. The complex tissue impedance 11 can be more rapidly and accurately measured between pulses through the energy recovery circuit 90, which efficiently captures the remaining energy in the generator circuit 110 at the end of a pulse and thus rapidly dampen the output signal of the generator circuit 110 and allows the fast application of an impedance measurement signal to the tissue 11. Although various embodiments of the present invention have been described in detail, it is evident that other modifications and adaptations of the invention will occur to those skilled in the art. However, it should be expressly understood that said modifications and adaptations are within the spirit and scope of the present invention.

Claims (28)

1. An electrosurgical generator for providing an output signal for use in the operation of a surgical operation on the mass of a tissue, comprising: a) DC regulating means for converting a first DC signal from a power source to a second DC signal having a predetermined voltage, including: inductive input means for reducing current ripple in the first DC signal, capacitive energy storage means for storing and releasing energy, switch means for alternately charging said capacitive energy storage means with the first DC signal and downloading the capacitive energy storage means to generate the second DC signal, and inductive output means to reduce the current ripple in the second DC signal; b) amplifying means for converting the second DC signal to the output signal having a predetermined frequency; and c) control means for providing control signals to the DC regulating means and the amplifying means to establish at least one of said predetermined voltage and said predetermined frequency.

2. The electrosurgical generator according to claim 1, wherein the electrosurgical generator further comprises a core material that magnetically couples said inductive input means and said inductive output means to substantially reduce current ripples in one of said means of inductive input and said inductive output means.

3. The electrosurgical generator according to claim 1, wherein the capacitive energy storage means comprise: a first capacitor; a second capacitor; and isolation transformer means, for isolating the current of the first DC signal from the current of the second DC signal.

4. The electrosurgical generator according to claim 3, wherein said isolation transformer means includes a primary winding connected in series to the first capacitor, said inductive input means and said power source, and a secondary winding connected in series to the second capacitor, said inductive output means and said amplifying means.

5. The electrosurgical generator according to claim 3, characterized in that it further comprises a core material that magnetically couples said isolation transformer means, said inductive input means and said inductive output means to substantially reduce current ripples in the media inductive input and inductive output means.

6. The electrosurgical generator according to claim 1, wherein the switching means comprise: a transistor connecting a junction between the inductive input means and the capacitive energy storage means for a return current path for the source of Energy; and a diode connecting a junction between the capacitive energy storage means and the inductive output means to the return current path.

7. The electrosurgical generator according to claim 1, wherein the switching means comprise: a transistor connecting a junction between the capacitive storage means and the inductive output means to a return current path.

8. The electrosurgical generator according to claim 1, wherein the switching means comprise: switch means capable of supporting the flow of current in both directions connecting a connection between the inductive input means and the capacitive storage means to a path current back to the power source; switch means capable of supporting the flow of current in both directions by connecting a junction between said capacitive storage means and said inductive output means to the return current path.

9. The system described according to claim 8, wherein the switching means are composed of one or more transistors.

10. The electrosurgical generator according to claim 1, wherein said amplifying means comprise: an amplifier input inductor to reduce the current ripple of the second DC signal; a resonant circuit connectable through the tissue mass, wherein said resonant circuit is connected in series to the input inductor of the amplifier and includes an inductor and a capacitor; and amplifier means switches to alternately connect and disconnect a current return path of the amplifying means to a junction between the input inductor and the resonant circuit thereby providing an output signal.

11. The electrosurgical generator according to claim 1, wherein the inductor and capacitor of the resonant circuit are selected to provide a substantially zero voltage through said amplifier switch means and a substantially zero instantaneous rate of change of the amplifier. voltage through the amplifier means switches prior to connection through the amplifier switch means thereby substantially reducing the dissipation of energy through the amplifier switch means.

12. The electrosurgical generator according to claim 1, characterized in that it further comprises energy recovery means electrically connected to said amplifier switch means to selectively store and release energy from the output signal.

13. An electrosurgical generator for providing an output signal for use in the operation of a surgical operation on the mass of a tissue, comprising: a) DC regulating means for converting a first signal DC from a power source to a second DC signal having a predetermined voltage; b) amplifying means for converting the second DC signal to the output signal having a predetermined frequency, including: an input inductor for reducing current ripple in the second DC signal, a resonant circuit connectable through the mass of a tissue , wherein said resonant circuit is connected in series to said amplifier input inductor and includes an inductor and a capacitor; and switch means for alternately connecting and disconnecting a current return path of said amplifier to a junction between the input inductor and the resonant circuit; and c) control means for establishing at least one of said predetermined voltage and said predetermined frequency.

14. The electrosurgical generator according to claim 13, wherein said inductor and said capacitor of the resonant circuit are selected in order to provide a substantially zero voltage through the switching means and a substantially zero instantaneous rate of change. of voltage across the switch means before connection by said switch means thereby substantially reducing the dissipation of energy by the switching means.

15. The electrosurgical generator according to claim 13, wherein said switch means includes a transistor.

16. The electrosurgical generator according to claim 13, characterized in that it also comprises energy recovery means electrically connected to the resonant circuit to selectively store and release the energy of the output signal.

17. The electrosurgical generator according to claim 13, wherein said inductive input means have a first number of windings and wherein the inductor of the resonant circuit has a second number of windings, wherein the first number of windings is substantially equal to said second number of windings.

18. The electrosurgical generator according to claim 12, wherein the energy recovery means are composed of: energy storage means with respect to said resonant circuit; means for restoring energy with respect to the control means, which alternately direct the excess energy of the resonant circuit towards the energy recovery storage means, and return the excess energy to the amplifier means.

19. The electrosurgical generator according to claim 18, wherein the energy storage means is an inductor.

20. The electrosurgical generator according to claim 18, wherein the switching means is a transistor.

21. The electrosurgical generator according to claim 16, wherein the energy recovery means are composed of: energy storage means with respect to said resonant circuit; means for restoring energy with respect to the control means, which alternately direct the excess energy of the output signal to the energy recovery storage means, and return the excess energy to the amplifier means.

22. The electrosurgical generator according to claim 21, wherein the energy storage means is an inductor.

23. The electrosurgical generator according to claim 21, wherein the switching means is a transistor.

24. An energy recovery circuit for an electrosurgical generator, which transmits an output signal of a predetermined frequency through a load, comprising: first and second means of storing energy with respect to the load; first switching means for directing a cycle of the output signal through the load and directing the unused energy of the output signal on the first energy storage means as a load, and alternatively initiating a transfer of the load to the second voltage means; and second switching means, which, together with the first switching means, initiate the transfer of the load from the second storage of energy to a next cycle of the output signal.

25. The energy recovery circuit according to claim 24, wherein the first and second energy storage means are connected in parallel with the load.

26. The energy recovery circuit according to claim 25, wherein the first energy storage means is an inductor, the second energy storage means is a capacitor, and the load is the tissue.

27. The energy recovery circuit according to claim 26, characterized in that it further comprises a first diode, which has a positive node connected to the inductor, the load and the capacitor, and a negative node connected to the first switching means; and a second diode with a positive node connected to the capacitor and a negative node connected to the periodic voltage source.

28. The energy recovery circuit according to claim 24, wherein the load is the tissue.