Abstract: An induction cooking appliance for operation at ultrasonic frequencies and including an improved work coil coupled in a solid state inverter circuit to generate an ultrasonic frequency magnetic field which is coupled to a metallic utensil through a non-electrically conductive cooktop. Coil losses are minimized, and coupling efficiency increased by forming the coil of solid conductor wound in a loose spiral, with the pitch of the spiral being related to the radial thickness of the conductor by a factor falling within a predetermined range. The loosely wound coil is held in a grooved dielectric support which insures proper turn spacing for the life of the appliance and which is immune to high temperatures which may be developed during operation of the coil. Means are provided under the support to minimize stray radiation and limit inductance variations which might otherwise result from nearby metallic members.

Abstract: An induction cooking appliance for operation at ultrasonic frequencies and including an improved work coil coupled in a solid state inverter circuit to generate an ultrasonic frequency magnetic field which is coupled to a metallic utensil through a non-electrically conductive cooktop. Coil losses are minimized, and coupling efficiency increased by forming the coil of solid conductor wound in a loose spiral, with the pitch of the spiral being related to the radial thickness of the conductor by a factor falling within a predetermined range. The loosely wound coil is held in a grooved dielectric support which insures proper turn spacing for the life of the appliance and which is immune to high temperatures which may be developed during operation of the coil. Means are provided under the support to minimize stray radiation and limit inductance variations which might otherwise result from nearby metallic members.

Abstract: An induction cooking appliance for heating a metallic utensil by means of an ultrasonic frequency magnetic field. The appliance includes a smooth, substantially non-metallic cooktop for supporting the utensil, and a work coil mounted below the cooktop for coupling the magnetic field to the utensil. The work coil is arranged in a solid state inverter circuit, including a gate controlled thyristor and a commutating capacitor, arranged to convert a d.c. voltage to current pulses of ultrasonic frequency. Simplified inverter protection circuits assure that conditions within the inverter do not exceed the component ratings. The protection circuits include a load sensing circuit for disabling the inverter when unloaded or when improperly loaded. An associated circuit responds to the power operating level of the inverter for varying the sensitivity of the load sensing circuit. Further protection is provided by an over-voltage limit circuit also adapted to disable the inverter.