Metal base cookware induction heating apparatus having improved power control circuit for insuring safe operation

• US 4,151,387 A
• Filed: 11/01/1974
• Issued: 04/24/1979
• Est. Priority Date: 04/06/1971
• Status: Expired due to Term

• Current Assignee: Environment One Corporation (Berkshire Hathaway Incorporated)
• Original Assignee: Environment One Corporation (Berkshire Hathaway Incorporated)
• Inventors: Peters, Philip H. Jr.
• Primary Examiner(s): Reynolds, Bruce A.
• Application Number:
  US05/520,117
• Time in Patent Office: 1,635 Days
• Field of Search: 321/18, 321/43-45, 363/96, 219/10.49, 219/10.77
• US Class Current: 219/626
• CPC Class Codes: F24C 7/02 using microwaves
• CPC Class Codes: G05D 23/19 characterised by the use of electric means G05D23/1393 takes precedence
• CPC Class Codes: G05D 23/1917 using digital means
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor
• CPC Class Codes: G05D 23/27 with sensing element responsive to radiation
• CPC Class Codes: G05F 1/56 using semiconductor devices in series with the load as final control devices G05F1/461 takes precedence
• CPC Class Codes: H02M 1/083 for the ignition at the zero crossing of the voltage or the current
• CPC Class Codes: H02M 3/135 using semiconductor devices only
• CPC Class Codes: H02M 5/45 using semiconductor devices only
• CPC Class Codes: H02M 7/515 using semiconductor devices only
• CPC Class Codes: H02M 7/525 with automatic control of output waveform or frequency H02M7/517 - H02M7/523 take precedence
• CPC Class Codes: H05B 2206/022 Special supports for the induction coils
• CPC Class Codes: H05B 6/062 for cooking plates or the like
• CPC Class Codes: H05B 6/1263 using coil cooling arrangements

Abstract

A metal based cookware induction heating apparatus having an improved power supply and control circuit comprised of a chopper inverter including a gate controlled power thyristor coupled to and supplying an induction heating coil with periodic energization currents. A full wave rectifier supplies rectified, unfiltered, unidirectional high voltage excitation potential to the chopper inverter which converts the excitation potential to a comparatively high frequency of the order of 20 kilohertz for supply to the induction heating coil. A gating circuit is provided for driving the chopper inverter directly from the rectified high voltage excitation potential supplied by the rectifier.

Claims

1. An improved power supply circuit and dv/dt control including including in combination, power supply terminal means connected across and supplying a thyristor semiconductor switching device connected in a power supply circuit, a snubbing circuit comprising a series connected resistor and capacitor connected in parallel circuit relationship across the thyristor semiconductor switching device for limiting the rate of rise of reapplied forward voltage across the thyristor semiconductor switching device, circuit means connected to said snubbing circuit for deriving an output dv/dt control signal representative of the rate of rise of reapplied forward voltage across the thyristor semiconductor switching device and means for applying said dv/dt control signal back to control operation of the thyristor semiconductor switching device in a direction to assure safe operation of the power supply circuit within the constraints dictated by the dv/dt characteristics of the thyristor.

2. A reliable solid state cooking appliance for inductively heating a cooking utensil comprising an induction heating coil mounted adjacent a substantially unbroken non-metallic utensil support and producing an alternating magnetic field, a static power conversion circuit including a power circuit controlled by solid state power device means for generating an ultrasonic frequency wave that drives said induction heating coil, and a control circuit operating at signal level and connected to selected points on said power circuit, said control circuit comprising a turn-on circuit for selecting the intervals of conduction of said solid state power device means, and further comprising protection circuit means for detecting predetermined abnormal power circuit conditions and modifying the operation of said control circuit to obtain reliable and automatic operation of said static power conversion circuit.

3. A cooking appliance according to claim 2 wherein said control circuit further includes a utensil presence detection circuit that senses the absence of a cooking utensil coupled with said induction heating coil and modifies the operation of said control circuit.

4. A reliable solid state cooking appliance for inductively heating a cooking utensil comprising an induction heating coil mounted adjacent a substantially unbroken non-metallic utensil support and producing an alternating magnetic field, a static power conversion circuit including a power circuit controlled by solid state power device means for generating an ultrasonic frequency wave that drives said induction heating coil, and a control circuit operating at signal level and including a turn-on circuit for selecting the intervals of conduction of said solid state power device means, and further including utensil presence detection circuit means for sensing a parameter at a selected point on said power circuit during a predetermined time interval and modifying the operation of said control circuit in response to a sensed parameter indicative of the absence of a cooking utensil coupled with said induction heating coil.