GB1482682A - Microwave oven - Google Patents

Abstract

1482682 Control systems for microwave ovens LITTON INDUSTRIES Inc 4 Dec 1974 [18 March 1974] 52535/74 Heading H2H A microwave oven has the source of microwave energy therefor energized in a series of pulses, the duty cycle of which is adjustably controllable. A magnetron 21 supplying energy for a microwave oven is energized from an A.C. supply 33 by way of a triac 23 and a transformer 25, the magnetron filament being continuously energized from the supply 33 by way of a second transformer 26. The duty cycle of the triac 23, and hence that of the magnetron 21 is controlled by an astable multivibrator 22 which generates firing pulses for the triac 23 at a frequency which is variable by means of a control 20 in the form of adjustable resistors 51, 52, the multivibrator 22 being energized from the A.C. supply 33 by way of a diode 37. The system also includes a timer motor 57 mechanically coupled to an ON-OFF switch 61 located in the supply line 34. With two adjustable resistors 51, 52 the operating frequency of the multivibrator 22 remains constant during adjustment of the resistors but if desired, one resistor only may be employed the output frequency of the multivibrator then varying with adjustment of the resistor. Alternatively a saw-tooth generator or other type of oscillator may be used instead of the multivibrator and the triac may be replaced by a pair of reverse parallel connected thyristors or thyratrons. Energization of a microwave oven by such means obviates the need for a conventional mode stirrer.