High frequency electrosurgical apparatus employing constant voltage

Claim 2

The electrosurgical generator and the electrosurgical instrument (11, 12, 13) according to claim 1, the apparatus comprising: modulator means (52) for providing a selectable DC voltage; generator means (53) for generating an AC waveform at a first frequency; and inverter means (55) having: a first input means coupled to an output of the modulator means (52); a second input means coupled to an output of the generator means (53); and an output means (54) providing a waveform having a frequency proportional to the frequency of the AC waveform and a substantially constant peak-to-peak voltage proportional to the selectable DC voltage.

Claim 3

The electrosurgical generator of claim 1 or 2, wherein the output voltage waveform provided by the apparatus is a square wave.

Claim 4

The electrosurgical generator of any of claims 2 or 3, wherein the modulator means (52) further comprises a control input terminal (51) for receiving a control signal.

Claim 5

The electrosurgical generator according to any of claims 2 to 4 wherein the modulator means (52) further comprises: a voltage supply node (61) for receiving a power supply voltage; a switch node (66); switch means (60) for oscillating between a conducting state in which the switch means (60) conducts the power supply voltage from the voltage supply node (61) to the switch node (66) and a nonconducting state in which the switch means (60) isolates the switch node (66) from the power supply voltage; a ground terminal (64) connected to a ground potential; rectifying means (65) connected between the ground terminal (64) and the switch node (66), the rectifying means (65) freely passing current from the ground terminal (64) to the switch node (66) and inhibiting the flow of current from the switch node (66) to the ground terminal (64); and a first inductor (62) connected between the switch node (66) and the modulator output (63).

Claim 6

The electrosurgical generator of claim 5 wherein: the control signal is a voltage control signal; and the switch means (60) further comprises means for receiving the voltage control signal from the control input terminal (51), the switch means (60) oscillating with a duty-cycle that is selected by the voltage level of the voltage control signal, the modulator output (63) having a voltage level that is determined by the duty-cycle.

Claim 7

The electrosurgical generator of claim 5 or 6 wherein the switch means (60) further comprises: a first transistor (72) having: a first base, a first collector connected to the voltage supply node (61), and a first emitter connected to the switch node (66); a second transistor (78) having: a second base, a second collector connected to the first base, and a second emitter connected to the voltage supply node (61); a third transistor (76) having: a third base, a third collector, and a third emitter; a first resistor (77) connected between the second base and the third collector; a second resistor connected between the switch node (66) and the third base; first means for providing for the passage of current between the control input node (51) and the third base; and second means for providing for the passage of current between the third emitter and the ground terminal (64).

Claim 8

The electrosurgical generator of claim 7 wherein the first means for providing for the passage of current comprises a third resistor (89).

Claim 9

The electrosurgical generator of claim 7 or 8 wherein the second means for providing for the passage of current comprises: a fourth resistor (81) connected between the third emitter and the ground terminal (64); and a first capacitor (82) connected between the third emitter and the ground terminal (64).

Claim 10

The electrosurgical generator of any of claims 7 to 9 further comprising: a fifth resistor (88) connected between the switch node (66) and the third emitter.

Claim 11

The electrosurgical generator of claim 10 further comprising: a sixth resistor (85) connected between the first base and the first emitter, the sixth resistor (85) discharging a first junction between the first base and the first emitter when the first transistor (72) is turning off; a seventh resistor (86) connected between the second base and the second emitter, the seventh resistor (86) discharging a second junction between the second base and the second emitter when the second transistor (78) is turning off; a Schottky diode (87) connected between the second base and the second collector for preventing the second transistor (78) from saturating; a second capacitor (79) connected between the second base and the third collector for providing charge to the second transistor (78) when the second transistor (78) is turning on; a third capacitor (74) connected between the voltage supply node (61) and the ground terminal (64); and a second inductor (73) connected between the voltage supply node (61) and a terminal (71) for receiving a power supply voltage.

Claim 12

The electrosurgical generator according to claim 5 wherein the switch means (60) further comprises: a first transistor (72) having: a first base, a first collector connected to the voltage supply node (61), and a first emitter connected to the switch node (66); a second transistor (78) having: a second base, a second collector connected to the first base, and a second emitter connected to the voltage supply node (61); a third transistor (76) having: a third base, a third collector, and a third emitter connected to the ground terminal (64); a first resistor (77) connected between the second base and the third collector; and first means connected to the third base for alternatingly providing a high output state to the third base and a low output state to the third base.

Claim 13

The electrosurgical generator of claim 12 wherein the first means comprises: a comparator (91) connected to the third base having an inverting input (99) and a non-inverting input (100); second means connected to the control input terminal (51) for alternatingly providing a higher voltage at the inverting input (99) than at the non-inverting input (100) and a higher voltage at the non-inverting input (100) than at the inverting input (99).

Claim 14

The electrosurgical generator of claim 13 wherein the second means further comprises: a second resistor (97) connected between the switch node (66) and the inverting input (99); and a third resistor (98) connected between the ground terminal (64) and the inverting input (99).

Claim 15

The apparatus of claim 13 or 14 wherein the second means further comprises: a fourth resistor (99) connected between the control input terminal (51) and the non-inverting input (100) for providing the voltage control signal to the comparator (91); a first capacitor (101) connected between the inverting input (99) and the non-inverting input (100); and a fifth resistor (102) connected between the switch node (66) and the non-inverting input (100).

Claim 16

The electrosurgical generator of any of claims 12 to 15 wherein the first means further comprises a sixth resistor (94) connected between the third base and the power supply node (61), and a power supply filter having: a seventh resistor (93) connected between the comparator (91) and the power supply node (61); and a second capacitor (92) connected between the comparator (91) and the ground terminal (64).

Claim 17

The electrosurgical generator of claim 16 further comprising: an eighth resistor (85) connected between the first emitter and the first base, the eighth resistor (85) discharging a first junction between the first base and the first emitter when the first transistor (72) is turning off; a ninth resistor (86) connected between the second emitter and the second base, the ninth resistor (86) discharging a second junction between the second base and the second emitter when the second transistor (78) is turning off; a Schottky diode (87) connected between the second collector and the second base for preventing the second transistor (78) from saturating; and a third capacitor (95) connected between the modulator output (63) and the ground terminal (64) for providing filtering of the selectable DC voltage.

Claim 18

electrosurgical generator according to any one of claims 1 to 17 comprising a conventional electrosurgical generator that outputs a voltage waveform greater than 120 volts root-mean-square at an impedance having a crest factor substantially greater than one, and an adaptor circuit (110) that converts the voltage waveform output of the electrosurgical generator to a clipped voltage waveform having an output voltage of less than 120 volts root-mean-square and a crest factor near unity.

Claim 19

electrosurgical generator as defined in claim 18 wherein the adaptor circuit (110) comprises: a transformer (117) having primary (118) and secondary (119) windings, the voltage output of the electrosurgical generator applied across the primary winding (118); a rectifier bridge (121 to 124) coupled to the secondary winding (119), the rectifier bridge having first (115) and second (116) output nodes for supplying the clipped voltage waveform and first (113) and second (114) bridge nodes; means coupled to the first (113) and second (114) bridge nodes for regulating the voltage across the first (115) and second (116) output nodes, the pair of electrodes of the electrosurgical instrument (11, 12, 13) adapted to be coupled to the output nodes (115a, 116a).

Claim 20

electrosurgical generator as defined in claim 19 wherein the means for regulating the voltage across the first (115) and second (116) output nodes comprises: a transistor (128) having a base, emitter and collector, the collector connected to the first bridge node (113) and the emitter connected to the second bridge node (114); a diode (125) having a preselected breakdown voltage, the cathode of the diode (125) connected to the collector and the anode of the diode (125) connected to the base, wherein the breakdown voltage determines root-mean-square voltage and the crest factor of the clipped voltage waveform; and a resistor (129) connected to the base of the transistor (128) and the second bridge node (114).

Claim 21

electrosurgical generator as defined in claim 19 or 20 wherein the secondary winding (119) further comprises a plurality of user-selectable taps (120), each of the plurality of taps (120) corresponding to a different ratio of secondary (119) to primary (118) windings.

Claim 22

electrosurgical generator as defined in any of claims 19 to 21 wherein the means for regulating the clipped voltage waveform across the first (115) and second (116) output nodes comprises a plurality of user-selectable diodes (125), each of the plurality of diodes having a different breakdown voltage, so that degree of clipping of a sinusoidal output voltage waveform of the electrosurgical generator can be varied.

Claim 23

An adaptor circuit (110) in combination with an electrosurgical generator connected to an electrosurgical instrument (11, 12, 13) and having an output impedance of greater than 20 ohms and that outputs a voltage waveform having a value greater than 120 volts root-mean-square at a frequency in the range of 100 kHz to 2 MHz, the adaptor circuit (110) characterized in that it converts the output voltage waveform of the electrosurgical generator to a clipped voltage waveform having a value less than 120 volts root-mean-square and a crest factor near unity.

Claim 24

The adaptor circuit (110) and electrosurgical generator according to claim 23 in combination with an electrosurgical instrument (11, 12, 13) having a pair of electrodes, wherein the adaptor circuit (110) comprises: a transformer having primary (118) and secondary (119) windings, the voltage output of the electrosurgical generator applied across the primary winding (118); a rectifier bridge (121 to 124) having first (115) and second (116) output nodes, coupled to the secondary winding (119), and first (113) and second (114) bridge nodes for providing a rectified voltage; and shunting means coupled between the first (113) and second (114) bridge nodes for regulating the voltage across the first (115) and second (116) output nodes by shunting excess current from the first bridge node to the second bridge node, the pair of electrodes of the electrosurgical instrument (11, 12, 13) adapted to be coupled to the output nodes (115a, 116a).

Claim 25

The adaptor circuit (110) according to claim 24 wherein the means for regulating the voltage across the first (113) and second (114) bridge nodes comprises: a transistor (128) having a base, emitter and collector, the collector connected to the first bridge node (113) and the emitter connected to the second bridge node (114); a diode (125) having a preselected breakdown voltage, the cathode of the diode (125) connected to the collector and the anode of the diode (125) connected to the base, wherein the breakdown voltage determines root-mean-square voltage and the crest factor of the clipped voltage waveform; and a resistor (129) connected to the base of the transistor (128) and the second bridge node (114).

Claim 26

The adaptor circuit (110) according to claim 24 or 25 wherein the secondary winding (119) further comprises a plurality of user-selectable taps (120), each of the plurality of taps (120) corresponding to a different ratio of secondary (119) to primary (118) windings.

Claim 27

The adaptor circuit (110) according to any of claims 24 to 26 wherein the means for regulating the clipped voltage waveform across the first (115) and second (116) output nodes comprises a plurality of user-selectable diodes (125), each of the plurality of diodes (125) having a different breakdown voltage, so that degree of clipping of the output voltage waveform of the electrosurgical generator can be varied.