1. In an RF generator including a RF power output transistor, a protection circuit for preventing secondary breakdown of said transistor conprising a. means for producing a gate pulse in phase with the collector voltage of said power transistor each time the collector voltage of said power transistor exceeds a preselected value; b. gate means receiving said gate pulse and a signal representing the collector current of said power transistor for producing an output signal only when said gate pulse and collector current are in phase and said collector current exceeds a preselected value; and c. means applying said output signal to said RF generator for reducing the output power thereof to a level within the safe operating limits of said transistor, whereby said transistor continues operation at a reduced level of power.

7. A protection circuit for use in an electrosurgical unit to prevent secondary breakdown during periods of reactive loading of a RF power output transistor used in said unit, said power output transistor having its base connected to the RF generator of the electrosurgical unit, said protection circuit comprising: a. collector current monitoring means for producing a current signal representative of the collector current of said power transistor; b. collector voltage monitoring means for producing a gate pulse in phase with the collector voltage when the collector voltage of said power transistor exceeds a preselected value; c. a transmission gate receiving said gate pulse and current signal and producing a correction signal only when said gate pulse and current signal are in phase and said current signal exceeds a preselected value; and d. means for applying said correction signal to said RF generator to bias off the drive thereof and reduce the power supplied to said power output transistor to within the safe operating limits of said transistor.