Abstract:
Until now, ohmic consumers have been used to abruptly complete the output signal in RF surgical generators. Considering an RF surgical generator comprising a power supply with at least one storage capacitor and a controllable switching device with at least one energy storage device (e.g., a transformer) by which an RF output signal that can be delivered to an RF surgical instrument is generated, it is suggested herein that a regenerative device be provided between the energy storage device and the storage capacitor. Furthermore, a control mechanism is used for controlling the switching device and the regenerative device such that, if the RF output signal is to be completed, the regenerative device is energized for at least part of the time, and the energy storage is at least partially discharged in the storage capacitor.

Description:
FIELD OF THE INVENTION 
     Embodiments of the invention relate to an RF (radio frequency) surgical generator as well as a method for driving such a generator. 
     BACKGROUND 
     Increasingly, RF surgical generators are used for tissue cutting and coagulating. Compared with mechanical incisions, haemostasis of the cutting edges is considered one of the advantages of RF surgical incisions, this haemostasis being due to thermal coagulation, in particular. In this case, the depth of the coagulation zone is largely dependent on the perfusion of the treated tissue, resulting in the requirement that the depth of the coagulation zone used by the RF surgical generators can be adjusted in as reproducible a manner as possible. In conjunction with this, the shape of the RF output signals of the RF surgical generator is of importance and, in particular, the ratio of peak value to effective value. Consequently, amplitude-modified RF voltages (currents) are selected, where the modulation is sufficient for the RF surgical generator to potentially also generate only a single cycle followed by a longer pause. 
     Another requirement is that the RF surgical generator be as highly efficient as possible because, if the efficiency is too low, any heat loss must be removed by elaborate cooling measures, which is not desirable in the operating room. 
     German Publication DE 102 18 895 A1 discloses an RF surgical generator to achieve greater efficiency in that the DC voltage power supply usually provided for such RF surgical generators can work in two modes of operation, i.e., on one hand, it can work as a power supply for the power oscillator (in a conventional manner) and, on the other hand, it can work in a mode in which an energy transfer from the power supply of the power oscillator back to the input of the DC voltage power supply takes place. In this case, substantial improvements in shaping short pulses are not possible. 
     German Publication DE 100 46 592 A1 discloses an RF surgical generator of the type addressed herein. In this generator, the ohmic resistance is withdrawn when the RF output signal is to be completed, said ohmic resistance being connected parallel to the consumer, as it were. The efficiency of this device, however, is minimal. 
     SUMMARY 
     An object of the embodiments of the invention is to provide an RF surgical generator of the aforementioned type, as well as a method for driving such a generator such that great efficiency and an exact and rapid shaping of the RF output signal can still be achieved. 
     This object is achieved by an RF surgical generator and method of operating said generator, wherein said RF surgical generator comprises a power supply with at least one storage capacitor, and comprising a controllable switching device with at least one energy storage, e.g., an output transformer, by which an RF output signal that can be delivered to an RF surgical instrument is generated. A regenerative device is connected between the energy storage and the storage capacitor and a control means is provided, said control means controlling the switching device and the regenerative device such that, if the RF output signal is to be completed, the regenerative device is energized for at least part of the time, and the energy storage is at least partially discharged in the storage capacitor. 
     Consequently, it is an essential aspect of the embodiments of the invention that the electrical, or also magnetic, energy that is stored in the usually provided dummy elements, e.g., the usually provided output transformer, is withdrawn from this energy storage, thus quickly resetting the RF output signal to zero. This energy that is delivered to the storage capacitor of the power supply is then available for a subsequent RF output signal. This increases the efficiency of the arrangement. 
     An improvement of signal controllability with—at the same time—minimal circuitry is given whenever a discharge device that drains residual energy from the energy storage is provided. To accomplish this, a transformation into thermal energy due to an ohmic load can also be used, ensuring that the oscillator will die out reliably. However, there remains a considerable increase of efficiency due to regeneration. Preferably, the discharge device is controlled by the control means such that the residual energy is drained following a partial discharge of the energy storage. 
     In a preferred embodiment, the energy storage comprises an output transformer, and the regenerative device comprises a separate winding on the output transformer. This way, it is possible to easily adjust the desired voltage conditions. 
     It is possible to accomplish regeneration via an electronic switch that is controlled by the control means. Alternatively, regeneration is possible via a diode line via which the energy storage is discharged upon the completion of the RF output signal. 
     Preferably, the storage capacitor of the RF surgical generator is arranged such that it—by the interposition of controlling elements—is able to absorb the excess energy of the output transformer. 
     The regenerative device comprises a DC/DC converter to perform an appropriate voltage adaptation. Said converter may be configured as a step-up chopper. 
     In an alternative embodiment, the regenerative device comprises a step-down chopper whose input voltage is adjusted to a constant voltage using an electronic switch. This embodiment of the circuit is particularly simple. 
     The method for driving an RF surgical generator comprising a power supply with at least one storage capacitor, and a controllable switching device with an output transformer, said device generating an RF output signal that can be delivered to an RF surgical instrument is characterized in that, for switching off the RF output signal, energy stored in the output transformer is delivered to the storage capacitor and stored in said storage capacitor. The advantages of this method have already been explained above. This applies, analogously, to corresponding developments of the method, which are apparent in view of the above-described circuit features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter, exemplary embodiments of the invention are explained in greater detail with reference to drawings, in which: 
         FIG. 1  is a circuit diagram of a first embodiment of the invention; 
         FIG. 2  is a circuit diagram of a second embodiment of the invention; 
         FIG. 3  is a circuit diagram of a third embodiment of the invention; 
         FIG. 4  is a circuit diagram of a fourth embodiment of the invention; 
         FIG. 5  is a time-dependency diagram of signal processes; and 
         FIG. 6  is a circuit diagram of a fifth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the description hereinafter, the same reference signs are used for components that are the same or that have the same function. 
       FIG. 1  shows a circuit comprising a power supply  10 , where only the DC/DC converter is identified with a capacitor C located at its output. Of course, additional converter devices are provided in order to supply power to the DC/DC converter from an AC main supply. 
     The generator comprises an oscillating circuit C R  and a (primary) winding W 1  of an output transformer T R  and is connected to the capacitor C via transistor T 2 . A control input “b” of transistor T 2  is connected to a control mechanism  20  that, consequently, can generate an oscillation due to an appropriate actuation of transistor T 2  in the oscillating circuit C R -W 1 , the oscillation can be delivered—via a secondary winding W A  and a series oscillating circuit L A , C A —as the output voltage U a  to an RF surgical instrument (not shown). 
     An additional winding W 2  of the transformer T R  is also connected to the capacitor C via diode D 1  and transistor T 1 , on one side, and via a direct line, on the other. The control input “a” of transistor T 1  is connected to the control mechanism  20 . A series circuit comprising a resistor R and transistor T 3  is provided parallel to the additional winding W 2 . A control input “c” of transistor T 3  is also connected to the control mechanism  20 . 
     Hereinafter, the function of the circuit in accordance with  FIG. 1  will be explained with reference to  FIG. 5 . 
     The control mechanism  20  generates the activation pulses n and n+1 that are delivered to the control input “b” of transistor T 2 . By activating transistor T 2 , the oscillating circuit C R , W 1  is excited and generates an output voltage U a . 
     To complete the oscillation of the oscillating circuit C R , W 1  the control mechanism  20  generates a signal “a” that activates transistor T 1 . As a result of this, only the additional winding W 2  is connected to the capacitor C via diode D 1  and transistor T 1  so that current I 1  flows, said current moving the energy stored in the transformer T R  into the capacitor C. 
     Following the relatively short control pulse “a” (see  FIG. 5 ), transistor T 3  is turned on by the control mechanism  20  via control input “c” of said transistor, so that only current I 2  flows through the resistor R, thereby converting a residual discharge of energy from the transformer T R  into thermal energy. Consequently, the output voltage U a  is completely set to zero; in which case a substantial quantity of the energy stored in the output transformer T R  is again available on the capacitor C to be used during a subsequent activation of transistor T 2  via a control pulse (pulse n+1). 
     The circuit in accordance with  FIG. 2  has a similar layout as the circuit in accordance with  FIG. 1  considering the power supply  10  and the output circuit. Referring to this circuit, the primary winding W 1  of the transformer T R  is connected to an upper pole of the capacitor C via transistor T 21  and to the lower pole of the capacitor C via transistor T 22 . The collector/emitter lines of the two transistors T 21  and T 22  are bridged by free-wheeling diodes. 
     The collector of the lower transistor T 22  is connected to the upper pole of the capacitor C via diode D 3 . The emitter of transistor T 21  is connected to the lower pole of the capacitor C via diode D 2 , said diode D 2  being bridged via a series circuit comprising a resistor R and transistor T 3 . 
     The current paths are indicated for explanation of the function of this circuit in accordance with  FIG. 2 . 
     When transistor T 21  and transistor T 2   2  are turned on, the result is current path  4 , said path  4  generating a (pulse-shaped) output voltage U a . To quickly complete this output pulse (after closing transistors T 21 , T 22 ) the energy contained as current I 1  in the transformer T R  is returned to the capacitor C via diodes D 2  and D 3 . To decrease any residual energy the control mechanism  20  activates transistor T 3 , so that the residual energy contained as current I 2  in the transformer T R  is converted into thermal energy via current path  6 . 
     The layout shown in  FIG. 3  is similar to the circuit in accordance with  FIG. 1  considering the generation of oscillations and considering the transformer T R . However, in this arrangement, the additional winding W 2  is connected to the capacitor C via a step-up chopper comprising diode D 1 , capacitor C H , inductor L H  and another diode D H . More precisely, a series circuit comprised of diode D 1  and capacitor C H  is provided parallel to the additional winding W 2 . One end of the coil L H  is connected to the coupling point between the diode and the capacitor, and the other end is connected to the capacitor C via diode D H . The coupling point between diode D H  and inductor L H  is connected to the other pole of the capacitor. C via transistor T 1 . 
     Furthermore, a series circuit comprising an ohmic resistor R and a transistor T 3  is connected in parallel to the additional winding W 2 . 
     Energization takes place in accordance with the diagram of  FIG. 5 ; however, it is also possible to turn on the regenerative transistor T 1 —different from the illustration of  FIG. 5 —as follows: 
     The circuit shown in  FIG. 3  comprising L H , T 1  and D H  represents a step-up chopper. This step-up chopper is able to reload energy from the storage capacitor C H  to the input capacitor C. Transistor T 1  can be turned on in pulse width modulation (PWM) mode, current regulation mode or a similar quasi-continuous mode of operation. The intent of the regulation of the step-up chopper is to maintain the voltage across the storage capacitor C H  constant and, accordingly, vary the choke current by means of L H . 
     The circuit shown in  FIG. 4  is different from that shown in  FIG. 3  in that capacitor C provided in the actual generator circuit is not used, but instead capacitor C Z  provided in an intermediate circuit for regenerating the energy stored in transformer T R  via the current I 1  is used. This circuit also shows that, in the embodiment of the invention, the element that absorbs the energy stored in the output transformer T R  and makes said energy available for repeated excitation and generation of an output voltage U A  is not important. 
     Considering the circuit shown in  FIG. 6 , again transistor T 2  is provided for excitation and generation of an output voltage U a , said transistor T 2  closing an electric circuit between the output capacitor C of the power supply  10  and the primary winding W 1  of the transformer T R  when turned on by signal “b” from the control mechanism  20 . 
     This arrangement comprises a series circuit that is connected to the capacitor C for regenerating the energy contained in the transformer T R  on the capacitor C, said circuit comprising a first diode D 11 , second diode D 12 , transistor T 1  and a coil L T . The connecting point between transistor T 1  and the coil L T  is connected to the lower pole of the capacitor C via diode D T . The coupling point between diode D 12  and transistor T 1  is connected to the lower pole of the capacitor C via capacitor C T . The connecting point between the diodes D 12  and D 11  is connected to the upper pole of the capacitor C via a series circuit comprising a resistor R and transistor T 3 . 
     Considering this circuit, transistor T 1  is responsible for regeneration and is driven via its control input “a” by the control mechanism  20  in PWM mode (or in another controlled mode, e.g., current mode or two-point regulation) such that the input voltage of the step-down chopper set up here is regulated to a constant voltage for charging the capacitor C. Other than that, the circuit is driven like the previously driven circuits, in which case—also in this circuit (as in  FIG. 2 )—the generator is not a sinewave generator, but is designed for single pulse excitation. Consequently, a capacitor parallel to the primary winding W 1  is not necessary in this embodiment. Here, the regenerated energy is restricted to the magnetizing energy stored in the transformer.