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Abstract

A microprocessor controlled electrosurgical generator provides plural ground-isolated and mutually isolated monopolar r-f cutting signals for respective surgical pencils to permit plural surgeons to use the same generator while maintaining independent control over output power and mode selection. A bipolar output signal is also isolated from ground and from the monopolar signals so that the removal of the dispersive patient return pad is not required when changing between monopolar and bipolar operation. Adjustment of the r-f cutting signal power level is effected by providing an adjustable d.c. bias level for an output amplifier. The d.c. bias level is derived from an a.c. control signal which is duty-cycle modulated in accordance with selected r-f power level settings. Digital phase control is employed to change the control signal duty cycle by subdividing the control signal cycle into precise count intervals and triggering a gate to pass the control signal through a rectifier to a filter for only the selected number of count intervals in each cycle as determined by a pre-settable counter. Negative feedback of the cutting signal to the input terminal of the output amplifier provides system stability during open circuit operation.

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