Abstract: The present invention relates to induction cooking appliances which provide a user with an improved set of information concerning the cooking capabilities of a piece of cookware to be used in conjunction with said appliance. In a further aspect, the present invention concerns an improved method for checking the cooking capabilities of a piece of cookware to be used in conjunction with an induction cooking appliance.

Abstract: A heating circuit for heating a conductive bowl includes a voltage source; a first heating coil provided between first and second nodes and being configured to heat the conductive bowl; a second heating coil provided between the second node and a third node and being configured to heat the conductive bowl; first capacitor and first switch provided in parallel between the first node and a fourth node; and second capacitor and second switch provided in parallel between the third node and the fourth node. The first and second heating coils define a circle-like shape having a center. The first and second heating coils are configured to be aligned to each other if one of the first and second heating coils is moved with respect to a line extending through the center of the circle-like shape.

Abstract: An induction heating cooker has a top plate, a heating coil, an inverter circuit, a pot type discriminator, a non-magnetic-metal buoyancy reducing plate having a high electrical conductivity, an infrared sensor, a temperature calculator, and a controller. The pot type discriminator judges whether a pot is made of a non-magnetic metal material having a high electrical conductivity, or a magnetic metal material or a non-magnetic metal lower in electrical conductivity than aluminum. The temperature calculator calculates the temperature of the pot from an output from the infrared sensor that detects infrared radiation from the pot. The controller controls an output from the inverter circuit according to a calculated temperature by the temperature calculator, and, when the pot is judged to be made of a non-magnetic metal material by the pot type discriminator, nullifies temperature detection made by the temperature calculator.

Abstract: Heating devices and methods which are particularly useful in vending machines for hot products. Products such as beverages contained in individual containers such as cans are rapidly heated to serving temperature by induction heating for delivery to a customer. Various types of products with different heating characteristics are rapidly heated without deleterious effects on the product by varying the power and timing of the inductive heating. The type of product is identified by indicia on the container which are automatically scanned prior to heating. The product containers may be agitated before, during and/or after heating to mix the contents and distribute heat evenly. The containers are heated in a manner to safely heat the product without overheating or causing damage to the container.

Abstract: Heating devices and methods which are particularly useful in vending machines for hot products. Products such as foods, including beverages, contained in individual containers such as cans are rapidly heated to serving temperature by induction heating for delivery to a customer. Various types of products with different heating characteristics are rapidly heated without deleterious effects on the product by varying the power and timing of the inductive heating. The type of product is identified by machine-readable indicia on the container which are automatically scanned prior to heating. The containers may be agitated before, during and/or after heating to mix the contents and distribute heat evenly. The containers are heated in a manner to safely heat the product without overheating or causing damage to the container.

Abstract: A heater for a hob or cooktop having a glass ceramic surface is disclosed, whereby a number of individual modules with induction coils are provided with converters and a converter control for each induction coil. The modules may be independently assembler and/or replaced, and are arranged close together beneath the glass ceramic hob and electrically connected to a busbar. Each module may be controlled separately. A heated surface of using various combinations of modules can thus be achieved.

Abstract: A heater unit is provided, the heater unit equipped with an induction heating coil and an electric heater selectively operated based on kind and state of a load of a cooking vessel placed on the heater unit. The kind is determined by an input current inputted when a load-type determination unit causes the induction heating coil to be operated and a resonance current flowing into the induction heating coil. The state is determined by a temperature change of the heater unit when a load-state determination unit allows the electric heater to generate heat, and the induction heating coil and the electric heater are selectively operated based on the determined kind and state of the load. Accordingly, a user needs not to scrupulously determine the kind of the cooking vessel and the electric cooker is not operated under a no-load state to prevent occurrence of safety accidents.

Abstract: A supply generator for an oscillating circuit, includes an inductance (L) and a resonant capacitor (C3, C4), for operation at a fixed frequency and also includes at least one pair of transistors (I2, I2), operated on a variable cyclic regime for modifying the power. The generator includes a first diode (D5) between a first transistor (I2) and the supply for the generator and a second diode (D4) between the junction point of the inductance (L) and the resonant capacitor (C3, C4) and the junction point of the first transistor (I2) and the first diode (D5). The invention is of particular use for supply of the cooking rings on an induction cooking hob.

Abstract: A food preparation system includes a non-contact power supply for energizing a cooking appliance. The food preparation system includes a communication system for enabling communication between a food appliance and the system. The appliance transmits an identifier to the system. If the appliance does not have a transmitter, the system attempts to determine the type of appliance from a characterization of the power consumption by the appliance. If the appliance cannot be characterized, the food preparation system can be operated manually.

Abstract: An induction-heating cooking apparatus and a method for operating the same are disclosed. Upon receiving a low-voltage signal in a high-output level state, the apparatus controls an output signal to allow an inverter to be operated only in a ZVS (Zero Voltage Switching) area. If an input voltage applied to a circuit is a low voltage, the apparatus compensates for the input voltage using a smaller one between a blocking voltage and an output control signal generated from the microprocessor, thereby limiting a compensation component. Therefore, the apparatus prevents the occurrence of a power loss caused by an excessive switching operation, and also prevents a switch from receiving a high instantaneous current, resulting in increased endurance of cooking appliances.

Abstract: The invention relates to an identification system for insert elements for tempering food accommodated in containers. Advantageously, the invention can be used in particular for short-term, economic and high-quality heating of prefabricated food wherein heating can be preferably carried out in induction ovens. According to the object, the respective configuration and if possible also the equipment with containers of such an insert element shall be allowed to be recognized and taken into consideration for tempering. At the same time, the insert elements have definitely arranged containers which can be fixed in receiving means. An appropriately equipped insert element can be introduced into an induction oven or a cooling device wherein the containers of a horizontal plane are positioned at the same time. According to the invention, at least one electromagnetically or magnetically detectable element is mounted on the insert elements each in a predeterminable position.

Abstract: A detector is operable to detect a displacement of a load by an ascending force based on a period of time from a time a heating output of an inverter drops from a predetermined level to a first level, to a time the heating output returns back to a second level larger than first level. Thereby, the detector distinguishes an intentional removal of the load from the displacement of the load by the ascending force. An induction heater including the detector reduces the displacement of the load by the ascending force and stops the heating of the load when the load is removed intentionally.

Abstract: An induction heating cooker includes an infrared sensor for sensing an infrared intensity from a load pot, a waveguide for guiding infrared radiation from the load pot to the infrared sensor, a first magnetism-proofing unit and a second magnetism-proofing unit for reducing magnetic fluxes leaking from a heating coil. Placement of the waveguide at a position lower than an upper surface of the second magnetism-proofing unit reduces self-heating of the waveguide due to magnetic flux supplied from the heating coil. As a result, a temperature rise of the infrared sensor due to radiation heat from the waveguide can be reduced, and an accuracy of sensing a temperature by the infrared sensor can be improved.

Abstract: An induction heating cooker includes a surface, a heating coil for inductionally-heating a load pan, an inverter for supplying a high-frequency current to the heating coil, an infrared detector which detects infrared radiation emitted from the load pan and is located under a top plate, a first temperature detector for detecting a temperature of the load pan based on an output of the infrared detector, a heating controller for controlling a power output from the inverter, a thermo-sensitive element for receiving heat from the top plate, and a second temperature detector for detecting a temperature of the load pan based on an output of the first thermo-sensitive element. This induction heating cooker detects a temperature change of the load pan accurately by detecting an infrared radiation from the load pan, and detects the temperature of the load pan by the heat conduction from the pan even if ambient light enters.

Abstract: An induction-heating cooking apparatus, operation of which is interrupted by container eccentricity is disclosed. Upon receiving an input signal varying with the degree of eccentricity of a container, the apparatus changes a reference signal for determining the presence or absence of a small load in proportion to a pulse-width control signal controlling the width of an inverter driving pulse. Although the eccentricity of the container occurs in a normal heating operation and completely escapes from a cook zone, the apparatus determines the occurrence of a no-load state, and interrupts an operation of an inverter circuit, resulting in increased stability of a circuit and a product.

Abstract: An induction heating apparatus with high safety is provided in which leakage current is prevented from flowing to the human body and there is no possibility of an electric shock even when an electrostatic shielding member does not sufficiently perform its function. The driving apparatus of the present invention is an induction heating apparatus in which the electrostatic shielding member is provided between an object to be heated and an induction heating coil where sensing portion for sensing the conduction condition of the electrostatic shielding member is provided, and driving portion for driving the induction heating coil is controlled through sensing by the sensing portion.

Abstract: An induction heating cooker capable of accurately discriminating whether the material of a cooking container placed in the induction heating cooker is magnetic or non-magnetic, using a phase change in a resonant capacitor voltage of an inverter circuit and a switching pulse signal of the inverter circuit, irrespective of the load of the cooking container, and a method for operating the induction heating cooker.

Abstract: An inverter circuit of an induction heating rice cooker which controls a switching frequency of an inverter in a variable manner according to a variation in an input voltage and drives the inverter at the controlled switching frequency. The inverter circuit comprises a power supply circuit for rectifying and filtering a commercial alternating current (AC) voltage to supply the input voltage to the induction heating rice cooker. The inverter performs a switching operation based on the input voltage from the power supply circuit to heat the rice cooker. The inverter circuit further comprises an inverter driving circuit for outputting a drive pulse to control the switching frequency of the inverter in the variable manner according to the input voltage from the power supply circuit and drive the inverter at the controlled switching frequency.

Abstract: An electric heater (10) incorporates at least one heating element (20), at least one wall member (16) upstanding in the heater, and a device (42) is provided for detecting a cooking utensil (6) supported on an upper surface (4) of a cooking plate (2) overlying the heater. The device (42) comprises at least one inductively-operating loop (44) of electrically conductive material having a plurality of portions (50, 52, 54) adapted to extend over and spaced from the at least one electric heating element (20) between fixed supporting regions (56, 58, 60, 62) on the at least one wall member (16). The at least one loop (44) of electrically conductive material is such that the plurality of portions (50, 52, 54) are substantially incapable of self-support as such at normal operating temperatures of the electric heater. The plurality of portions (50, 52, 54) are supported by elongate members (64, 66, 68) of heat-withstanding material.

Abstract: An induction heating device prevents an object to be heated from being displaced and buoyed from a mounting surface due to an mutual action of repulsive forces between the object to be heated and an induction heating coil. The induction heating device includes a source-current detector for detecting a source current input to a high-frequency inverter including the induction heating coil and an inverter circuit, a source-current change detector for measuring a change against time of a magnitude of the source current to detect a displacement and buoying of the object to be heated, such as a cooking pot, and a change examining unit. The controller controls an output of the high-frequency inverter in response to a detection result of the change examining unit. The induction heating device prevents the cooking pot from being displaced and buoyed even if the pot is not touched by a user at startup of heating or during the heating operation, and is inexpensive and safe.

Abstract: An induction heatable body (22) that quickly heats to a desired temperature, retains heat long enough to be used in almost any application, and develops no “hot spots” even when heated by a heating source having an uneven magnetic field distribution. The induction-heatable body (22) achieves the foregoing while remaining relatively lightweight, inexpensive and easy to manufacture. The induction-heatable body (22) includes a plurality of induction-heatable layers (32a, b, c) each sandwiched between alternating layers of heat retentive material (34a, b, c). The induction-heatable layers (32a, b, c) consist of sheets of graphite material that can be inductively heated at magnetic field frequencies between 20 and 50 kHz. The heat-retentive layers (34a, b, c) consist of solid-to-solid phase change material such as radiation cross-linked polyethylene.

Abstract: An induction heating apparatus can heat aluminum pot etc. with pot vibration noise being suppressed. During a turn-on time of second switching device 57, an energy is accumulated at choke coil 54, and at the same time a resonant current with a shorter period than the turn-on time of second switching device 57 or a driving time of first switching device 55 is generated at heating coil 59, so that during turn-off of second switching device 57, i.e., during on-time of first switching device 55, the energy accumulated at choke coil 54 is transferred to second smoothing capacitor 62. And then the output power is supplied from smoothing capacitor 62 to heating coil 59, thereby reducing the pot vibration noise, which is caused by pulsating current of input voltage.

Abstract: Methods and Apparatus for detecting the presence of a conductor near an inductive coupling loop are disclosed. The method includes supplying an excitation to the coupling loop, measuring the signal distortion induced by the excitation signal, and monitoring the distortion in the signal for a change in harmonic content.

Abstract: An induction heating method and device comprise an inductive heat source (120) having a controller (130), a resonant converter (125) and an induction coil (80). The controller (130) generates a variable frequency variable duty cycle control voltage in response to a power setting. The variable duty cycle of the control voltage decreases in response to an increase in the variable frequency of the control voltage. In response to the control voltage, the resonant power converter (125) generates an output between a first node (126) and a second node (128). Coupled between the first and second nodes (126, 128), the induction coil (80) varies the amount of heat it produces in response to the output power.

Abstract: An induction heating and control system and method have enhanced reliability and advanced performance features for use with induction cooking devices, such as induction heating ranges. Enhanced performance is facilitated via the use of an induction heating system which integrates voltage management, power management, thermal management, digital control sensing and regulation systems, and protection systems management.

Abstract: An induction heating device for heating cooking vessels includes at least three concentric inductors and implements a step of heating a load. For a load covering at least three inductors, at least one intermediate inductor that is covered and that is determined in such a manner as to homogenize the input of heat to the load is not energized during the heating step. Applications of the device include domestic hot plates.

Abstract: An induction heating device includes a plurality of induction coils connected to a single high-frequency power source and each being able to be ON/OFF controlled by a switch. A current is selectively fed only to desired part of the induction coils or to all of the induction coils connected in parallel. The coils are driven by a current fed thereto at the same time in the same phase. The device may include inverters for controlling power to be fed coil by coil. The device is free from interference and irregular heating and can readily cope with a change in a heating range while controlling power coil by coil.

Abstract: An induction heating and control system and method have enhanced reliability and advanced performance features for use with induction cooking devices, such as induction heating ranges. Enhanced performance is facilitated via the use of an induction heating system which integrates voltage management, power management, thermal management, digital control sensing and regulation systems, and protection systems management.

Abstract: When a pan made of a non-magnetic material, such as aluminum, is used for cooking while the temperature is being controlled, a notice is made to the user to the effect that the temperature control function has been stopped and that the temperature should be manually adjusted, when the material detection section detects that the pan is made of a non-magnetic material or a pan floating phenomenon has occurred, in order to prevent abnormal increase in the temperature of the pan due to incorrect temperature detection caused by the pan floating phenomenon, a set temperature is lowered.

Abstract: The invention concerns an induction system for heating, re-heating and keeping warm a food container combining an armature beneath the container, an induction device supporting the container optimised for the safety of the user, the electromagnetic compatibility, and preserving the induction device since the induction is activated only in the presence of an appropriate armature.

Abstract: The invention concerns an induction cooking hob with multiple inductors fed at the same frequency or multiples of a common fundamental frequency to avoid beat frequencies. Separate generators are provided for two or more heaters. A high-power heater is provided with two or more inductors. To provide maximum power, the second inductor of the high-power heater may be supplied with power switched from the generator for a different heater.

Abstract: A magnetic induction heating assembly is provided which comprises a heater circuit and an induction heatable device including a continuous coil formed of electrically conductive material; the coil has terminal ends, and a conductive assembly including a switch component is connected between the terminal ends. The heater circuit includes a magnetic field generator, a detector operable to detect a heater circuit parameter related to the impedance presented to the heater by the induction heatable device, and control circuitry capable of altering the magnitude of the magnetic field generator in response to detection of the parameter.

Abstract: Temperature self-regulating food delivery systems are provided having a magnetic induction heater (32, 126) and an associated food container (76, 124) equipped with an essentially permanent ferromagnetic heating element (82, 100, 128). The heater (32, 126) and heating elements (82, 100, 128) are designed so as to heat the element (82, 100, 128) to a user-selected regulation temperature when the elements (82, 100, 128) are coupled with the heater's magnetic field, and to maintain the temperature in the vicinity of the regulation temperature indefinitely temperature regulation is a heating achieved by periodically determining at least two parameters of the heaters resonant circuits related to the amplitude of the resonant current passing therethrough during heating and responsively altering the field strength of the magnetic field. Preferably, the value of the resonant circuit amplitude and the rate of change of the amplitude are determine.

Abstract: An induction heating and control system and method have enhanced reliability and advanced performance features for use with induction cooking devices, such as induction heating ranges. Enhanced performance is facilitated via the use of an induction heating system which integrates voltage management, power management, thermal management, digital control sensing and regulation systems, and protection systems management.

Abstract: A device for determining the location of cooking utensils on a cooking hob comprising a plurality of thermal cells distributed in matrix formation below a heat-resistant surface on which the cooking utensil can be located in random manner, the determination of its location, form and dimensions enabling those thermal cells lying below the utensil to be energized, the same thermal cells being also individually used for this determination.

Abstract: A temperature-regulating induction heating system is provided which comprises an induction heater (20) having apparatus (36, 38, 40) for receiving RFID transmissions and an induction heatable object (22) with an RFID tag (50). The heater (20) includes a component (28) for generating a magnetic field, control circuitry including a microprocessor (32) coupled with the component (28) for selectively initiating and terminating generation of a magnetic field; the receiving apparatus (36, 3 8, 40) provides information to the microprocessor (32) causing initiation of a heating algorithm for the object (22). In preferred forms, the tag (50) and apparatus (36, 38, 40) are designed for two-way information transfer, thereby permitting continuous updating of the information carried by tag (50). In this way, if induction heating of the object (20) is interrupted, it maybe resumed to nevertheless achieve a desired regulation temperature.

Abstract: A compact rice cooker with excellent rice cooking performance while preventing boiling-over is presented. This rice cooker includes a main body 31, a lid for covering the top of the main body, an inner pan detachably accommodated in the main body, a bottom heating coil for induction heating of the inner pan, a control unit for controlling high frequency power to be supplied to the bottom heating coil, and a rice gruel detecting unit disposed in a steam tube of the lid, and therefore electric power supply is controlled by the control unit depending on the detection state by the rice gruel detecting unit. The rice gruel detecting unit makes use of movement of the float due to the rise of rice gruel, and the lid is formed in a compact size, and boiling-over is prevented, so that tasty rice can be cooked.

Abstract: Temperature self-regulating food delivery systems are provided having a magnetic induction heater (32, 126) and an associated food container (76, 124) equipped with an essentially permanent ferromagnetic heating element (82, 100, 128). The heater (32, 126) and heating elements (82,100, 128) are designed so as to heat the element (82, 100, 128) to a user-selected regulation temperature when the elements (82, 100, 128) are coupled with the heater's magnetic field, and to maintain the temperature in the vicinity of the regulation temperature indefinitely temperature regulation is a heating achieved by periodically determining at least two parameters of the heaters resonant circuits related to the amplitude of the resonant current passing therethrough during heating and responsively altering the field strength of the magnetic field. Preferably, the value of the resonant circuit amplitude and the rate of change of the amplitude are determine.

Abstract: Temperature self-regulating food delivery systems are provided having a magnetic induction heater (32, 126) and an associated food container (76, 124) equipped with an essentially permanent ferromagnetic heating element (82, 100, 128). The heater (32, 126) and heating elements (82,100, 128) are designed so as to heat the element (82, 100, 128) to a user-selected regulation temperature when the elements (82, 100, 128) are coupled with the heater's magnetic field, and to maintain the temperature in the vicinity of the regulation temperature indefinitely temperature regulation is a heating achieved by periodically determining at least two parameters of the heaters resonant circuits related to the amplitude of the resonant current passing therethrough during heating and responsively altering the field strength of the magnetic field. Preferably, the value of the resonant circuit amplitude and the rate of change of the amplitude are determined.

Abstract: A compact rice cooker with excellent rice cooking performance while preventing boiling-over is presented. This rice cooker comprises a main body 31, a lid 36 for covering the top of the main body 31, an inner pan 32 detachably accommodated in the main body 31, a bottom heating coil 33a for induction heating of the inner pan 32, control means for controlling high frequency power to be supplied to the bottom heating coil 33a, and rice gruel detecting means disposed in a steam tube 47 of the lid 36, and therefore electric power supply is controlled by the control means depending on the detection state by the rice gruel detecting means. The rice gruel detecting means makes use of move of the float 48 due to rice gruel, and the lid 36 is formed in a compact size, boiling-over is prevented, so that tasty rice can be cooked.

Abstract: A compact rice cooker with excellent rice cooking performance while preventing boiling-over is presented. This rice cooker comprises a main body, a lid for covering the top of the main body, an inner pan detachably accommodated in the main body, a bottom heating coil for induction heating of the inner pan, a control unit for controlling high frequency power to be supplied to the bottom heating coil, and a rice gruel detector disposed in a steam tube of the lid, and therefore electric power supply is controlled by the control unit depending on the detection state by the rice gruel detecting means. The rice gruel detector makes use of move of the float due to rice gruel, the lid is formed in a compact size, and boiling-over is prevented, so that tasty rice can be cooked.

Abstract: An induction heating or cooking apparatus comprises an inductive heating coil (L), means (CT) for sensing the current I.sub.s of an AC supply applied to the heating coil (L), means (VR) for selecting the desired heat output of the apparatus, means (APC) for comparing the sensed current with in output of the selecting means (VR), and means (RL1) for varying a the voltage of the supply to the heating coil (L) in accordance with the value of an error signal output from the comparing means (APC). Thus, the temperature which the base of a cooking utensil (P) stood on the coil (L) reaches is independent of the material of the utensil.

Abstract: An induction heating power supply is disclosed. It includes a power circuit having at least one switch and a power output. The output circuit includes an induction head. The output circuit is coupled to the power output. A controller has at least one feedback input connected to the output circuit, and has a control output connected to the switch. The controller predicts the switch zero crossing and preferably soft switches the switch. Current feedback is obtained from a coil placed between the bus bars. Each bus bar is comprised of multiple plates to increase current capacity.

Abstract: For use in the heating of foodstuffs by induction, use is made of an energy converter between energy taken from the mains supply via a rectifier and a high frequency oscillation. Such a converter is frequently based on the maintenance of an oscillation in a parallel resonant circuit (CR, LR) which may be disposed in a converter bridge (S1, S2, S3, S4) of controlled switches. It has turned out to enhance the efficiency considerably to let the parallel resonant circuit be series connected to a self-inductance L1 which connects it to the DC source UDC. A series resonant circuit is thereby created which is active during supply of energy and which in a simple fashion reduces the load on the participating switches.

Abstract: A high-frequency inverter having a simple circuit construction capable of executing a constant-frequency operation and a zero-volt switching operation and an induction heating cooker using the high-frequency inverter are disclosed. The high-frequency inverter is comprised of an inverter circuit for converting a direct current from a DC power source into a high-frequency current and a control circuit for controlling the inverter circuit. The inverter circuit is comprised of: a one-transistor inverter constructed of a heating coil whose one terminal is connected to one terminal of a DC power source, a first switching element connected in series between the other terminal of the heating coil and the other terminal of the DC power source, and a first resonance capacitor connected so as to form a resonance circuit with the heating coil; and a series circuit connected in parallel with the heating coil and constructed of a second switching element and a second resonance capacitor.

Abstract: The present invention relates generally to inductive heating, and more particularly to an apparatus and method for non-contact detection and inductive heating of heat retentive food server warming plates used in institutional food service. The invention provides a non-contact detection and control circuit for an inductive heating apparatus for heating an inductively reactive heat radiating element built into a warming plate. The warming plate employed by the invention has an integral inductively reactive heat radiating element that is brought to a desired heating temperature such as 450.degree. F. In a preferred embodiment, the apparatus is configured like a conventional industrial cook stove and surface. Underneath the surface is a magnetic inductive coil controlled by the invention for inductively heating a reactive ferromagnetic heat radiating element that is placed on the surface.

Abstract: A heat retentive, temperature self-regulating, food retaining apparatus (10) includes a body (12), heat retentive core (14) and magnetic induction heating element (16). The body (12) includes a substantially rigid, heatable, food-contacting wall (18) defining a cavity (24). The core (14) is positioned in the cavity (24), and in thermal contact with the wall (18) for selective heating of the wall (18). The core (14) includes a solid state phase change material for storing latent heat during a solid-to-solid phase transformation at a phase transformation temperature. A resilient material is in contact with the phase change material to permit expansion of the phase change material during a phase transformation. The heating element (16) is in thermal contact with the core (14) for heating the core (14) to a temperature above the phase transformation temperature to effect a phase transformation in the phase change material.

Abstract: The induction cooking apparatus includes an input filter for filtering supplied power, a first inverter module having a first working coil, a second inverter module having a second working coil, and a common switching section. The common switching section and the first and second inverter modules are connected in series with the input filter, and the first and second inverter modules operate cooperatively with the common switching section to energize the first and second working coils.

Abstract: A method is described of processing an electrical signal output from a sensor coil located in an electric heater for use under a cook top in a cooking appliance. The sensor coil is employed to operate a switch to switch on and off a heating element in the heater in accordance with placement and removal of a cooking utensil on and from the cook top. The sensor coil is arranged in the heater within magnetic influence of the electrical heating element, the heating element comprising a material which is ferromagnetic below and substantially non-ferromagnetic above a predetermined temperature within an operating temperature range of the heater. The occurrence of an increase in output signal level from the sensor coil is detected and closure of the switch is effected. Subsequently, the occurrence of a decrease in output signal level from the sensor coil is detected and opening of the switch is effected.

Abstract: A ripple current generator for an induction heating apparatus includes a resonant circuit with a current injecting self-inducting coil (6), a capacitor (13), an induction heating coil (14) and a high-frequency controlled power switch (12). The current injecting self-inducting coil (6) is saturable and mounted in series with a parallel assembly consisting of two arms; a first arm (B.sub.1) containing the switch (12) and a second arm (B.sub.2) containing a capacitor (13) mounted in series with the induction heating coil (14). The self-inducting coil includes a magnetic circuit that automatically reaches saturation during the resonance phase of the oscillating circuit. The generator is useful in household cooking appliances such as induction plates, cookers or deep fryers, as well as industrial induction heating equipment for treating metal components.