Patent ID: 6203541
Filing Date: 2001-03-20
Classification: A61B

Abstract:
An automatic circuit that controls a surgical instrument having a pair of bipolar electrodes, the circuit comprising:means for measuring the current between the pair of electrodes, said measuring means including;means for generating a constant voltage;a transformer having a primary winding and a secondary winding, said primary winding having a signal end for receiving a signal and a return end, said secondary winding coupled to the pair of electrodes; anda resistive element in series with said generating means and said signal end, wherein a voltage developed across said signal end and said return end of said primary winding is representative of a measured current between the pair of bipolar electrodes;an impedance detection circuit in electrical communication with said measuring means for calculating the impedance based on the measured current, the impedance detection circuit generating a first signal indicative of the calculated impedance;a comparator in electrical communication with the impedance detection circuit, the comparator processing the first signal and generating an activation signal if the calculated impedance falls within a predetermined range of impedance values and generating a deactivation signal if the calculated impedance exceeds a deactivation threshold; anda controller in electrical communication with the comparator for receiving the activation and deactivation signals and transmitting a first control signal to a radiofrequency energy output stage to activate the electrodes in response to the activation signal and transmitting a second control signal to the radiofrequency output stage to deactivate the electrodes in response to the deactivation signal.