Surgery – Instruments – Electrical application
Reexamination Certificate
1998-05-21
2001-06-26
O'Connor, Cary (Department: 3736)
Surgery
Instruments
Electrical application
Reexamination Certificate
active
06251106
ABSTRACT:
FIELD OF THE INVENTION
A constant power control circuit for an electrosurgical generator and a method for maintaining the electrical power output of an electrosurgical generator at a generally constant level throughout a given tissue impedance range.
BACKGROUND OF THE DISCLOSURE
An electrosurgical generator is used in surgical procedures to deliver electrical energy to the tissue of a patient. An electrosurgical generator often includes a radio frequency generator and its controls. When an electrode is connected to the generator, the electrode can be used for cutting or coagulating the tissue of a patient with high frequency electrical energy. During normal operation, alternating electrical current from the generator flows between an active electrode and a return electrode by passing through the tissue and bodily fluids of a patient.
The electrical energy usually has its waveform shaped to enhance its ability to cut or coagulate tissue. Different waveforms correspond to different modes of operation of the generator, and each mode gives the surgeon various operating advantage. Modes may include cut, coagulate, a blend thereof, desiccate, or spray. A surgeon can easily select and change the different modes of operation as the surgical procedure progresses.
In each mode of operation, it is important to regulate the electrosurgical power delivered to the patient to achieve the desired surgical effect. Applying more electrosurgical power than necessary results in tissue destruction and prolongs healing. Applying less than the desired amount of electrosurgical power inhibts the surgical procedure. Thus, it is desirable to control the output energy from the electrosurgical generator for the type of tissue being treated.
Different types of tissues will be encountered as the surgical procedure progresses and each unique tissue requires more or less power as a function of frequently changing tissue impedance. Even the same tissue will present a different load impedance as the tissue is desiccated.
Two conventional types of power regulation are used in commercial electrosurgical generators. The most common type controls the DC power supply of the generator by limiting the amount of power provided from the AC mains to which the generator is connected. A feedback control loop regulates output voltage by comparing a desired voltage with the output voltage supplied by the power supply. Another type of power regulation in commercial electrosurgical generators controls the gain of the high-frequency or radio frequency amplifier. A feedback control loop compares the output power supplied from the RF amplifier for adjustment to a desired power level. Generators that have feedback control are typically designed to hold a constant output voltage, and not to hold a constant output power.
U.S. Pat. Nos. 3,964,487; 3,980,085; 4,188,927 and 4,092,986 have circuitry to reduce the output current in accordance with increasing load impedance. In those patents, constant voltage output is maintained and the current is decreased with increasing load impedance.
U.S. Pat. No. 4,126,137 controls the power amplifier of the electrosurgical unit in accord with a non linear compensation circuit applied to a feedback signal derived from a comparison of the power level reference signal and the mathematical product of two signals including sensed current and voltage in the unit.
U.S. Pat. No. 4,658,819 has an electrosurgical generator which has a microprocessor controller based means for decreasing the output power as a function of changes in tissue impedance.
U.S. Pat. No. 4,727,874 includes an electrosurgical generator with a high frequency pulse width modulated feedback power control wherein each cycle of the generator is regulated in power content by modulating the width of the driving energy pulses.
U.S. Pat. No. 3,601,126 has an electrosurgical generator having a feedback circuit that attempts to maintain the output current at a constant amplitude over a wide range of tissue impedances.
None of the aforementioned U.S. Patents include a constant power control circuit that provides for a generally constant output power while also providing a linear adjustment to account for the unique waveform crest factors associated with different operational modes.
The preferred constant power control circuit and method provided herein allows for output power control by way of a unique and simple linear conversion circuit coupled with protection circuitry that prevents the electrosurgical generator from being over-driven during high and/or low impedance loading. The preferred constant power control circuit also reduces the severity of exit sparking by responding quickly to high impedance indications while nonetheless maintaining substantially increased power levels throughout a predetermined patient tissue impedance range.
SUMMARY OF THE INVENTION
A constant power control circuit for use with an electrosurgical generator. The constant power control circuit and method may be included as an integral part of the overall electrosurgical generator's circuitry, or may be designed as a separate unit that connects to, and controls, an electrosurgical generator. The constant power control circuit and method may be embodied through a variety of analog and/or digital circuit components or arrangements, including software running on computational and memory circuitry.
The constant power control circuit and method maintain the output power of the electrosurgical current at a generally constant level over a finite patient tissue impedance range. The preferred patient tissue impedance range is about 300 to 2500 ohms.
The constant power control circuit and method provide the capability to control the output power of the electrosurgical generator without having to actually monitor the amplitude of both the output current and output voltage. This allows for a simple constant power control circuit and method which operate to control the power output without having to calculate the actual power output of the electrosurgical generator.
While the constant power control circuit may be used to control electrosurgical generators of varying designs, it is preferred that the electrosurgical generator includes a power selection system wherein the user may initialize, set, monitor, and/or control the operation of the electrosurgical generator. It is also preferred that the power selection system produces a control voltage signal that acts to control a high voltage direct current supply which in turn acts to supply a high voltage signal to an output switching radio frequency stage. Then output switching radio frequency stage creates an electrosurgical energy between two output electrodes. The preferred electrosurgical generator need not be limited to these three functional elements, for example the electrosurgical generator could also include additional safety, monitoring, signal modification/conditioning, and/or feedback circuitry or functional elements/processes. The actual electrosurgical generator's design may include the use of digital components and signaling and/or analogue components and signaling, or may be embodied, completely or partially within a software process running on hardware components.
The constant power control circuit includes a current sampling circuit, a linear conversion circuit, and a feedback correction circuit. The current sampling circuit is coupled to one of the output electrodes, and functions so as to produce a sampled current signal that is proportional to the average current flowing through the output electrode.
The linear conversion circuit which is connected to the current sampling circuit internally generates one or more multiplier reference signals and one or more offset reference signals, each of which is used to modify the sampled current signal in accord with the crest factor associated with the electrosurgical energy output by the electrosurgical generator; the modified signal being a linear converted signal.
The feedback correction circuit which is electrically connected to receive the linear converted
Becker Daniel J.
Klicek Michael Steve
Carter Ryan
O'Connor Cary
Sherwood Services AG
LandOfFree
Electrosurgical generator power control circuit and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrosurgical generator power control circuit and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrosurgical generator power control circuit and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2474593