Electrosurgical generator power control circuit and method

• US 5,772,659 A
• Filed: 09/26/1995
• Issued: 06/30/1998
• Est. Priority Date: 09/26/1995
• Status: Expired due to Term

• Current Assignee: Covidien AG (Medtronic Plc)
• Original Assignee: Valleylab Inc. (Medtronic Plc)
• Inventors: Becker, Daniel J., Klicek, Michael Steve
• Primary Examiner(s): Bahr, Jennifer
• Assistant Examiner(s): CARTER, RYAN CHRISTOPHER
• Application Number:
  US08/533,891
• Time in Patent Office: 1,008 Days
• Field of Search: 606/34, 606/35, 606/38, 606/32, 606/42, 322/7, 322/27, 322/44, 323/322, 323/340, 323/911, 323/312, 323/315
• US Class Current: 606/34
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 2018/00875 Resistance or impedance

Abstract

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 value throughout a given tissue impedance range are disclosed. The constant power control circuit and the method recognize and use the unique and simple linear characteristics associated with certain electrosurgical generator designs to monitor and control the electrical power output without having to calculate or monitor the actual output power. The constant power control circuit includes a current sampling circuit, a linear conversion circuit, and a feedback correction circuit. The constant power control circuit may also include protection circuitry that prevents the electrosurgical generator from being over-driven during high and/or low impedance loading, and reduces the severity of exit sparking by providing a quick response to high impedance indications while nonetheless maintaining increased power levels throughout a preset, nominal impedance range. The constant power control circuit and method may be included as an integral part of the overall electrosurgical generator'"'"'s circuitry, or may be embodied 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.

Claims

1. A constant power control circuit for use in an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes, the constant power control circuit comprising:

a current sampling circuit inductively coupled to one output electrode, the current sampling circuit producing a sampled current signal proportional to an average current flowing through the output electrode;

a linear conversion circuit electrically connected to the current sampling circuit for generating a linear converted signal, wherein the linear conversion circuit includes;

a linear multiplier generating means for generating a multiplier reference signal;

a linear offset generating means for generating an offset reference signal;

a multiplier, electrically connected to the linear multiplier generating means, for multiplying the sampled current signal and the multiplier reference signal to produce a multiplied signal; and

a summer, electrically connected to the linear offset generating means, for summing the offset reference signal and the multiplied signal to produce the linear converted signal; and

a feedback correction circuit electrically connected to receive the linear converted signal from the linear conversion circuit and the control voltage signal from the power selection system for producing a feedback control signal which is supplied to the power selection system to control the amount of electrosurgical energy created, wherein the feedback correction circuit includes;

a subtractor, electrically connected to receive the linear converted signal and the control voltage signal, for determining a difference in amplitude between the control voltage signal and the linear converted signal and producing a delta signal proportional to the difference; and

an adder, electrically connected to receive the delta signal and the control voltage signal, for adding the delta signal to the control voltage signal and producing the feedback control signal.

2. The constant power control circuit for an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes of claim 1, wherein the output switching radio frequency stage has a primary transformer winding, and wherein the feedback correction circuit further includes:

a high impedance reference generator, electrically connected to receive the control voltage signal, for generating a high impedance reference signal;

a connector for electrically connecting the feedback correction circuit to the primary transformer winding;

a comparator, electrically connected to the connector and to receive the high impedance signal, for comparing the amplitude of the high impedance reference signal to the voltage across the primary transformer winding and producing a high impedance detection signal; and

a reducer, electrically connected to receive the high impedance detection signal and the feedback control signal, for reducing the amplitude of the feedback control signal when the high impedance detection signal indicates that the voltage across the primary transformer winding is greater than the high impedance reference signal.

3. The constant power control circuit for an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes of claim 1, wherein the feedback correction circuit further includes:

a maximum control voltage reference generator, electrically connected to receive the control voltage signal, for generating a maximum control voltage reference signal; and

a switcher, electrically connected to receive the maximum control voltage reference signal and the feedback control signal, for substituting the maximum control voltage reference signal for the feedback control signal when the feedback control signal is greater in amplitude than the maximum control voltage reference signal.

4. The constant power control circuit for an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes of claim 1, wherein the power selection system has a plurality of operational modes and wherein the linear multiplier generating means generates a unique multiplier reference signal for each operational mode, and the linear offset generating means generates a unique offset reference signal for each operational mode, and wherein the linear conversion circuit further includes:

a plurality of multipliers, wherein there is one multiplier for each operational mode and each multiplier multiplies the sampled current signal and the unique multiplier reference signal associated with one operational mode to produce a unique multiplied signal for that operational mode;

a plurality of summers, wherein there is one summer for each operational mode and each summer sums the offset reference signal associated with one operational mode and the unique multiplied signal associated with that operational mode to produce a unique linear converted signal for that operational mode;

a mode monitor, adapted to be electrically connected to the power selection system, for identifying the operational mode and producing an identified operational mode signal;

a signal selector, electrically connected to receive the identified operational mode signal and the unique linear converted signal from each of the summers, for selecting the unique linear converted signal associated with the identified operational mode, and causing that linear converted signal to be supplied to the feedback correction circuit.

5. A constant power control circuit for an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes, wherein the power selection system has a plurality of operational modes and the output switching radio frequency stage has a primary transformer winding, and wherein the constant power control circuit comprises:

a current sampling circuit adapted to be inductively coupled to one output electrode, the current sampling circuit producing a sampled current signal proportional to an average current flowing through the output electrode;

a linear conversion circuit electrically connected to the current sampling circuit for generating a linear converted signal, wherein the linear conversion circuit includes;

a linear multiplier generating means for generating a plurality of unique multiplier reference signals, wherein there is one multiplier reference signal for each operational mode;

a linear offset generating means for generating a plurality of unique offset reference signals, wherein there is one offset reference signal for each operational mode;

a plurality of multipliers, electrically connected to the linear multiplier generating means and to receive the sampled current signal, wherein there is one multiplier for each operational mode and each multiplier multiplies the sampled current signal and the unique multiplier reference signal associated with one operational mode to produce a unique multiplied signal for that operational mode;

a plurality of summers, electrically connected to the linear offset generating means and to each multiplier, wherein there is one summer for each operational mode and each summer sums the offset reference signal associated with one operational mode and the unique multiplied signal associated with that operational mode to produce a unique linear converted signal for that operational mode;

a mode monitor, adapted to be electrically connected to the power selection system, for identifying the operational mode and producing an identified operational mode signal;

a signal selector, electrically connected to receive the identified operational mode signal and the unique linear converted signal from each of the summers, for selecting the unique linear converted signal associated with the identified operational mode, and causing that linear converted signal to be supplied to the feedback correction circuit; and

a feedback correction circuit electrically connected to receive the linear converted signal from the linear conversion circuit and adapted to receive the control voltage signal from the power selection system for producing a feedback control signal which is adapted to be supplied to the power selection system to control the amount of electrosurgical energy created, wherein the feedback correction circuit includes;

a subtractor, electrically connected to receive the linear converted signal and the control voltage signal, for determining a difference in amplitude between the control voltage signal and the linear converted signal and producing a delta signal proportional to the difference;

an adder, electrically connected to receive the delta signal and the control voltage signal, for adding the delta signal to the control voltage signal and producing the feedback control signal;

a maximum control voltage reference generator, electrically connected to receive the control voltage signal, for generating a maximum control voltage reference signal;

a switcher, electrically connected to receive the maximum control voltage reference signal and the feedback control signal, for substituting the maximum control voltage reference signal for the feedback control signal when the feedback control signal is greater in amplitude than the maximum control voltage reference signal

a high impedance reference generator, electrically connected to receive the control voltage signal, for generating a high impedance reference signal;

a connector adapted for electrically connecting the feedback correction circuit to the primary transformer winding;

a comparator, electrically connected to the connector and to receive the high impedance signal, for comparing the amplitude of the high impedance reference signal to the voltage across the primary transformer winding and producing a high impedance detection signal; and

a reducer, electrically connected to receive the high impedance detection signal and the feedback control signal, for reducing the amplitude of the feedback control signal when the high impedance detection signal indicates that the voltage across the primary transformer winding is greater than the high impedance reference signal.

6. A method for maintaining a generally constant output power from an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes, the method including the steps of:

inductively coupling to one output electrode;

sensing the current flowing through the output electrode;

producing a sampled current signal proportional to the average current flowing through the output electrode;

generating a multiplier reference signal;

generating an offset reference signal;

multiplying the sampled current signal and the multiplier reference signal;

then

summing the offset reference signal to the product to produce a linear converted signal;

connecting to the control voltage signal from the power selection system;

determining the difference in amplitude between the control voltage signal and the linear converted signal;

adding the difference determined by the subtraction means to the control voltage signal to produce a feedback control signal, and

supplying the feedback control signal to the power selection system to control the amount of electrosurgical energy created.

7. The method for maintaining a generally constant output power from an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes of claim 6, wherein the output switching radio frequency stage has a primary transformer winding, and wherein the method further includes the steps of:

generating a high impedance reference signal;

connecting to the primary transformer winding;

comparing the amplitude of the high impedance reference signal to the voltage across the primary transformer winding; and

reducing the amplitude of the feedback control signal when the voltage across the primary transformer winding is greater than the high impedance reference signal.

8. The method for maintaining a generally constant output power from an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes of claim 6, the method further including the steps of:

generating a maximum control voltage reference signal; and

substituting the maximum control voltage reference signal for the feedback control signal when the feedback control signal is greater in amplitude than the maximum control voltage reference signal.

9. The method for maintaining a generally constant output power from an electrosurgical generator having a power selection system that produces a control voltage signal to control a high voltage direct current supply which supplies a high voltage signal to an output switching radio frequency stage thereby creating an electrosurgical energy between two output electrodes of claim 6, wherein the power selection system has a plurality of operational modes and wherein the method further includes the steps of:

generating a plurality of unique linear multiplier reference signals, one for each operational mode;

generating a plurality of unique linear offset reference signals, one for each operational mode;

multiplying the sampled current signal, separately and concurrently, with each of the unique multiplier reference signals to produce a plurality of unique multiplied signals, one for each operational mode;

summing each of the unique multiplied signals with the offset reference signal associated with the same operational mode to produce a plurality of unique linear converted signals, one for each operational mode;

connecting to the power selection system to identify the operational mode selected;

selecting the unique linear converted signal that matches the identified operational mode; and

then

causing that linear converted signal to be supplied to the feedback correction circuit.