Valleylab, Inc.

Sherwood Services Ag

Daniel J Becker

Michael S Klicek

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.

Electrosurgical generator power control circuit and method

Apparatus monitors RF return current to maximize the AC signal of impedance at two return electrodes. A transformer with driving and driven windings isolates ESU and patient. At ends of the driving winding are signal and ground terminals joined to the return electrodes with capacitors returning current. An AC coupling capacitor at the signal terminal has a timing circuit in sync to the voltage wave and relative to impedance of the return electrodes. Microprocessing the voltage at the signal terminal of the driving winding watches impedance and determines if the RF return current path is adequate. Voltage detection within the timing circuit has a voltage shaping circuit. A voltage comparator after the voltage detection forms a square wave. A current detection circuit and a coupling capacitor allow AC flow to the driving winding. Current shaping circuit in the current detection circuit has a voltage comparator at the output to form a square wave. Phase detection at the voltage and current detection circuits outputs filters the phase difference that is sampled and held as DC input to a switch, with an output and a few inputs to DC voltages. Phase locking an oscillating voltage source directly and/or through the sample and hold or DC switch tunes oscillation frequency and maximizes the voltage detection circuit output. Monitoring the return current with a signal from the voltage detection circuit connected to an oscillating voltage that is phase locked to the current phase therein shows that no phase difference and maximum signal voltage occur simultaneously.

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Broomfield, CO, United States of America

Daniel J Becker