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A developmental single-element induction range appliance with a smooth-surface ceramic cooktop is described. The appliance demonstrates the versatility of induction cooking and characteristic features of safety, cleanliness, high efficiency, and rapid response. Tests indicate that performance surpasses that of conventional range elements of equal power input. The circuit is designed to achieve minimum cost. A self-excited SCR inverter operates near 22 kHz to produce a sinusoidal magnetic field for heating. Full rectified line voltage is applied at all power levels to avoid the need for dc-to-dc conversion. Power is stepwise controlled over a wide range by switching capacitance in the RF circuit. Contact arcing is prevented by turning off power between switch positions. Full load power is 1600 W at a line voltage of 120 V. Input power decreases to a low standby level when no cooking utensil is on the cooktop. The appliance includes a pan temperature control. Infrared (IR) energy emanating from the pan bottom passes through the cool IR transmissive cooktop to a simple detection system which actuates the inverter to hold pan temperature within a few percent of a selected level from 70Â°C to 175Â°C.
Date of Publication: Nov. 1974