Radiofrequency electrosurgical generator with current control

A radio knife comprising a cutting handpiece and a plate powered by an electronic circuit comprising:

• a rectifier circuit fed by mains voltage that supplies rectified pulsating voltage to a radiofrequency circuit;
• said radiofrequency circuit suited to issue an output current signal with a constant frequency feeding the radio knife by means of a radiofrequency transformer,
• said radiofrequency circuit having a MOSFET piloted by a pilot to a circuit comprising a quartz-operated oscillator,
• said pilot circuit being connected to a microprocessor current control circuit which takes a signal from a current sensor present downstream in respect to said MOSFET and suited to maintain the current of said radiofrequency circuit limited to a value compatible with the power dissipatable by said MOSFET independently of any variation in the circuit load impedance,
• said impedance comprising also a patient's body part impedance positioned between the radio knife and the circuit closing plate,
• wherein said pilot circuit feeds said MOSFET with a frequency substantially of 4 MHz, said frequency being equal to the frequency of the current present in said handpiece, and said electronic circuit generates power greater than 100 W.

A radio knife having a radio frequency (RF) power input and being carried by a cutting hand piece for performing surgery on a body part of a patient representing a variable load impedance and a conductive plate for contacting the patient and closing an electronic circuit comprising:

• a rectifier circuit for producing a rectified pulsating voltage;
• an RF circuit coupled to the rectifier having an output for producing RF power sufficient to effect hemostasis at a selected voltage and current level and at a substantially constant frequency selected to produce said hemostasis without producing necrosis;
• an RF transformer coupled between the RF output and the power input of the knife for raising the voltage of the RF power output to said selected level;
• the RF circuit including a MOSFET current source having an output circuit coupled to the output of the RF circuit and an input, and an oscillator coupled to the input for modulating the MOSFET to the selected frequency, said MOSFET for producing the selected output current;
• a current sensor located in the output circuit of the MOSFET for producing an output indicative of the current in the MOSFET output circuit;
• and
• a microprocessor control responsively coupled to the current sensor and operatively coupled to the oscillator for producing a current limiting signal for controlling the oscillator gating the MOSFET, such that the selected current produced in the output circuit of said MOSFET is limited to a value compatible with the MOSFET and which selected current is independent of variations in the load impedance.