US 3,946,738 A · Leakage current cancelling circuit for use with electrosurgical instrument

Abstract

Circuitry for cancelling leakage current is disclosed. The leakage cancelling circuit is utilized in conjunction wih the active or patient electrodes of an electrosurgical instrument used in electrosurgery. In electrosurgery, a radio frequency current is passed through a patient between an active electrode and a patient electrode with the active electrode determining the point where surgery is performed and the patient electrode being made surgically inactive by large patient contact area. Current leakage at the electrodes is caused by stray capacity to ground in an isolated system and excessive leakage from the active electrode to ground can cause surgery to be performed without a patient connection while excessive leakage from the patient electrode to ground can cause RF burns to the patient and perhaps to operating room personnel having contact with the patient. In one embodiment, current leakage is cancelled by addition of current to the patient connection in correct phase and magnitude to cancel the existing patient leakage currents, the added current being supplied through circuitry that includes a capacitor in series with the tertiary winding on the output power transformer supplying current to the active and patient electrodes. In a second embodiment, a series LC circuit is placed in parallel with the stray capacitance to cancel the same.

Claims8

Dependent claims

The combination comprising:

an electrosurgical instrument having an active electrode and a patient electrode;
a power transformer having an isolated output circuit connected to said active and patient electrodes for supplying current thereto;
means for supplying power to said power transformer;
and,
a leakage current cancelling circuit for use in cancelling leakage current at said isolated output circuit, said cancelling circuit comprising means for offsetting leakage current caused by stray capacitance to ground at said output circuit, said offsetting means including inductive and capacitive elements connected with one side of said output circuit and ground and having values selected to accomplish said leakage current cancellation.

2 more elements

Dependencies are inferred from the claim text.

Leakage current cancelling circuit for use with electrosurgical instrument

Life of this patent

Leakage current cancelling circuit for use with electrosurgical instrument

Life of this patent

Abstract

Claims8