CONSTANT OUTPUT ELECTROSURGICAL UNIT
BACKGROUND OF THE INVENTION
This invention relates to electrosurgical units, and 5 more particularly to such units with a continuously controllable output voltage whose level remains at a substantially constant value independent of the load.
It has been found that tissue cutting can be accomplished by applying an unmodulated RF carrier to a 10 patient, while coagulation of blood vessels can be achieved by utilizing pulse modulated RF voltage signal. To achieve such electrical signals, there are presently available electrosurgical units which generally provide both an unmodulated and a modulated output 15 voltage, which may be selectively used for tissue cutting or tissue coagulation. The amplitude of the output level of the voltage desired for a cutting or a coagulation procedure varies depending upon the depth of cut, the impedance provided by the patient, and numerous 20 other factors relating to the electrode shape, environment and the particular operating procedure. Accordingly, it is necessary to provide some type of an intensity control whereby the amplitude of the output signal can be controlled. In some electrosurgical units, such 25 intensity control is available only in discrete steps. The electrosurgical unit contains an oscillator with an output tank circuit, and connected to the tank circuit are a number of taps with a rotating dial switch connectable to the individual taps. The voltage level is selected by 30 placing the dial at an appropriate tap. However, because of the many variations in the operating procedures, such discrete steps may not provide sufficient accuracy of control and may cause unwanted problems during its use. A further problem with existing electro- 35 surgical units concerns maintaining the selected output desired. By using the intensity control, the particular output level can be selected for the cutting or coagulation procedure. However, once the output voltage is applied to the patient by means of a hand piece such as 40 a probe or forceps, the patient acts as a load across the output of the electrosurgical unit which causes the output voltage level to drop. Such drops have provided great changes in the desired output level and often necessitate the operator to continuously reset the voltage 45 level as the procedure is carried out. It therefore required the surgeon himself, or an associate, continuously monitor the voltage output level of the electrosurgical unit and continuously make appropriate adjustments as the load on the unit changes. This monitoring 50 requires extra time and skill, and frequently may require the availability of an additional nurse or attendant. Should the voltage output not be monitored, the large variations in the voltage output can cause possible damage or harm to the patient by providing excessive depth 55 of cutting or an improper amount of coagulation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrosurgical unit which avoids the afore- 60 mentioned problems of prior art devices.
It is another object of the present invention to provide an electrosurgical unit with a substantially constant output voltage level which is independent of the load.
Yet a further object of the present invention is to 65 provide an electrosurgical unit which provides a continuously adjustable output voltage level for both cutting procedures and coagulation procedures.
Still a further object of the present invention is to provide an electrosurgical unit which produces an unmodulated RF carrier for use in cutting procedures and a pulse modulated RF voltage for use in coagulation procedures, and wherein the output voltage level can be preset and maintained at a substantially constant value independent of the load.
Another object of the present invention is to provide an electrosurgical unit which provides a high ratio of peak to average voltage output thereby providing a great amount of discrimination between the cutting and the coagulation voltages.
A further object of the present invention is to provide an electrosurgical unit which contains a low source impedance, and utilizes inverse feedback to maintain a substantially constant voltage independent of the load.
These objects are achieved in accordance with a preferred embodiment of the present invention wherein there is provided an electrosurgical unit producing an output voltage to a load, and including an oscillator producing an output signal at a given frequency. A switching circuit is coupled to the oscillator for providing an unmodulated RF carrier voltage from the oscillator for use in cutting procedures and a pulse modulated RF voltage from the oscillator for use in coagulation procedures. A feedback circuit is coupled from the output to the input of the oscillator to maintain the selected output voltage level from the unit at a substantially constant value independent of the load.
In order to control the output voltage level, the feedback circuit includes a sampling means coupled to the oscillator output for providing a signal proportional to the output voltage. A control circuit is coupled to the oscillator and responds to the proportional signal for changing the voltage produced by the oscillator in a direction opposite to any change in the proportional signal.
The control circuit includes an amplifier means having its control electrode connected to receive the proportional signal and its output electrode connected to control the oscillator. An intensity control means is interconnected to the control electrode for determining the output level from the unit. This provides a continuously variable output voltage level.
BRIEF DESCRIPTION OF THE DRAWINGS
With the above and additional objects and advantages in view, as will hereinafter appear, this invention comprises the devices, combinations and arrangements of parts hereinafter described by way of example and illustrated in the accompanying drawings of a preferred embodiment in which:
FIG. 1 is a block diagram of the electrosurgical unit of the present invention;
FIG. 2 is a detailed circuit diagram of the electrosurgical unit of the present invention;
FIG. 3 is a circuit diagram showing the feedback circuit alone;
FIG. 4 is a graph useful in explaining the operation of the electrosurgical unit of the present invention; and
FIGS. 5 and 6 represent graphs showing results obtained by the use of electrosurgical units in accordance with the present invention.
DESCRIPTION OF THE PREFERRED
Referring now to FIG. 1, there is shown a block diagram of an electrosurgical unit and including an