Abstract: An induction heating cooker has a rectifier (13) for producing pulsating DC current, an inverter (14) which receives the pulsating current given from the rectifier (13) and produces a high frequency output current and a load circuit (15) including an output coil (21) and a resonance capacitor (22) connected in series to each other to receive high frequency output signal from the inverter, and the variation or adjustment of output electromagnetic power is made by changing duty ratio of the high frequency output current of the inverter by giving variable duty ratio setting signals to switching elements (Qa, Qb) in the inverter 14; the frequency of the high frequency output current of the inverter 14 is fixed, and therefore, unpleasant interference sound is not generated at parallel simultaneous operation.

Abstract: An induction heating apparatus comprises a heating coil and a transistor which is connected to a direct current power source in series thereto to form an inverter for converting the direct current to an alternating current, and furthermore, a first coupling coil for supplying a forward base current to the transistor is coupled with the heating coil inductively and a second coupling coil for supplying a inverse base current for the transistor is also coupled to the heating coil inductively, and the inverter is controlled by a switching device which is controlled by a control circuit.

Abstract: A multi-unit induction heating apparatus for cooking applications comprises a plurality of inverter units for generating high frequency energy, each of the inverters having first and second input terminals, the first input terminals being coupled respectively through first circuits to a first terminal of a low frequency power source, the second input terminals being coupled together to a common circuit node which is connected through a second circuit to a second terminal of the power source. The apparatus further includes a like plurality of manually operated switches respectively connected in the first circuits and a like plurality of first high frequency noise rejection filters connected respectively in the first circuits. The second circuit includes a common, high frequency noise rejection filter.

Abstract: An induction heating apparatus including a thyristor adapted to receive power from a power source, a gating control circuit for generating gating pulses for application to the gating control terminal of the thyristor, a commutating circuit which commutates off the thyristor, and a differentiator connected across the anode and cathode terminals of the thyristor to detect the power consumption of an inductively heated cooking ware. The gating control circuit comprises a gating pulse generator and a smoothing circuit for filtering the signal from the differentiator into a d-c signal which is compared with a reference level to detect the deviation of the power consumption from the reference value. The gating pulse generator is responsive to a potential at the anode of the thyristor to initiate timing action to determine the interpulse period or turn-off time of the thyristor and also responsive to the deviation of power consumption to vary the interpulse period.

Abstract: An induction heat cooking apparatus includes an inverter which generates ultrasonic frequency energy for heating a magnetic load by induction, and a small load detection circuit. The detection circuit includes a comparator which compares the input and output parameters of the inverter and latches a bistable device when the input power is smaller than the output parameter. The bistable device shuts down the inverter to prevent inadvertently placed small utensil objects from being excessively heated.

Abstract: A plurality of switches each is provided in the vicinity of each of a plurality of heater coils of an induction heating apparatus, and responsive to removel of a cooking implement from a corresponding heater coil for being rendered open. A plurality of timers each is connected to each of the switches and causes the heater coil to be de-energized when the cooking implement is kept away from the heater coil for more than a predetermined time period.

Abstract: A multiple-load induction heating cooking apparatus comprises two or more induction heating commutation circuits each having the junction between its commutating inductor and capacitor manually selectively connected by corresponding one of a plurality of interconnecting switches equal in number to the commutation circuits to form a series-connected LC circuit to a high frequency energy source. The potential at the common point of connection is compared with a reference potential to produce an error signal which is used to control the frequency of the energy source so that the potential at the common point is maintained constant regardless of the magnitude of induction heating loads.

Abstract: An induction heating apparatus comprising a pair of inversely parallel-connected gate-controlled switching devices connected to an alternating current source, a resonant circuit including an induction heating coil and a variable frequency gating circuit for firing the switching devices to generate oscillations through the conducting device and the induction heating coil. The switching devices are gated into conduction in succession in a first order during the positive half cycle of the alternating current and in a reversed order during the negative half cycle. A zero crosspoint detector is provided to inhibit gating when the source voltage is near zero crosspoint level and to control the gating frequency in accordance with the instantaneous value of the source voltage to increase the turn-off time of the switching devices for lower input source voltage.

Abstract: A protection device for a thyristor inverter circuit of an induction heating cooking oven wherein commutation failure of a thyristor is detected by determining that the conduction period of the thyristor is outside a predetermined period or that a voltage applied to the thyristor is outside of a predetermined magnitude. The protection device deactuates the inverter to prevent breakdown of the thyristor and reduces the number of operations of the circuit breaker which is a final protection device. Additionally provided are linked switch actuator apparatus for placing a switch for actuating a thyristor control circuit in a state in which it is always actuated in advance of the actuation of a switch for a heating coil in order to prevent occurrance of a transient high voltage due to the switching of an inductive load in the inverter circuit, and an overheating protection circuit for detecting an abnormal temperature rise of the heating coil and an abnormal load condition to deactuate the inverter.

Abstract: An induction heating apparatus includes a saturable reactor having a pair of rectangular ferrite cores. An air gap is provided in each ferrite core to provide a gradually increasing saturation characteristic on the magnetization curve of the cores. A pair of series-connected load windings is coiled around each core and a control winding is coiled around a common magnetic path of the cores. A power control circuit produces a DC control current that passes through the control winding. The high frequency energization current is passed through the load windings. Means are provided to control the DC control current at a desired setting. Preferably, the actual power level is detected to control the DC current through a feedback loop.

Abstract: A pan detector for an induction heating apparatus of the type having an induction heating coil adapted to electromagnetically couple to a cooking vessel comprises a first, vertically movable magnet and a second, fixed magnet spaced therefrom and a reed switch disposed between the first and second magnets. Upon the placement of a cooking vessel of magnetic metal in overlying relation to the heating coil, the first magnet moves upwardy by attraction between the bottom wall of the cooking vessel and the first magnet to result in a change in magnetic flux level in the neighborhood of the reed switch. The reed switch operates in response to the change in magnetic flux level to permit and prevent, respectively, energization of the heating coil. The first and second magnets have their poles oriented in opposition to each other to provide repulsion therebetwen to increase the attraction.

Abstract: An electrically conductive material is heated by Joule heat generated by an eddy current loss and a hysteresis loss which are invited by a magnetic field injuced in the material by a current flowing in proximity to the material. The power output of the heating equipment is varied either electrically or mechanically while maintaining the inductance of the induction heating coil substantially constant.