Abstract: An induction heating apparatus comprises a rectifier (2) for rectifying a voltage from an AC mains supply, a resonance circuit formed by an induction heating coil (4) and a capacitor (4), a semiconductor switching device (6) connected in circuit with the resonance circuit to the output of the rectifier, a diode (7) coupled in anti-parallel relationship with the switching device (6), and a circuit (17; 117, 118) for driving the switching device into conduction at a controlled frequency. Further provided is a transformer (14) which derives a low-frequency energy from the AC mains supply (1). A second coil (9) is electromagnetically coupled with the heating coil (4) for deriving a high-frequency energy. The low- and high-frequency energies are coupled by diodes (10, 11, 15, 16; 132, 133) to the driving circuit to provide power necessary to effect the conduction of the switching device.

Abstract: An induction heating device makes use of a bridge inverter and has a DC power source, a plurality of switching elements forming a bridge inverter, and a circuit for detecting the turn-off of the switching elements. In order to detect the turn-off of the switching elements, an improved turn-off detection circuit is employed and an improved control circuit is installed to prevent the circuit from malfunctioning owing to external noise.

Abstract: In an induction heating apparatus wherein heat is generated in a magnetic material by eddy currents produced by high frequency magnetic field of a heating coil (32), zero crossing point of the voltage developed in the heating coil (32) is detected and the pulse-width of a transistor (33) is controlled in synchronism with the detected zero crossing point to provide wide range power output control.

Abstract: A plurality of magnetic field sensors are mounted adjacent the periphery of an induction heating coil of flat, spiral configuration which is energized by ultrasonic frequency energy to generate a time-varying magnetic field. The magnetic field sensors are connected in a ciruit to produce an output signal when a magnetic utensil load is placed asymmetrically with respect to the center of the induction heating coil. In response to sensor output exceeding a predetermined value a warning indication is provided. The ultrasonic energy level is reduced in response to the warning indication to minimize radio interference which would otherwise occur due to leakage magnetic flux.

Abstract: An induction heating cooking apparatus includes a pan supporting plate made of a flat sheet of a heat-resistant dielectric material, a heating coil for induction heating disposed below the pan supporting plate, and touch pads each constituting a capacitor-pair formed by first, second and third electrodes. The touch pads when including three pads respectively serves for turning on a power supply, for turning off the power supply, and for setting a power level to a predetermined level. The induction heating or the supply of the power is permitted to take place only when the touch pad is first touched and followed by touching the touch pad. The first electrodes of the touch pads are provided on the upper surface of the pan supporting plate, and are enclosed by guard rings of a conductive material to prevent erroneous operation.

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: Induction heating apparatus using gate-controlled switching devices includes a zero crossing point detector for detecting the occurrence of each zero crossing point of high frequency energization current, and a timing circuit which provides timing action in response to the detected zero crossing point. The timing action is controlled by a power control circuit which detects the level of energy delivered to a load within a range from the inherent turn-off time of the gate-controlled switching devices to a desired value.

Abstract: A frequency inverter using thyristor(s), wherein a gate circuit produces both positive triggering signals and negative reverse-bias signals by utilizing outputs of the timer in order not to fail turnings of the thyristor, and the timing of both signals are automatically controlled to by synchronized with oscillation of the resonance circuit connected to the anode and the cathode of the thyristor, so as to respond to a change of load condition, so that always suitable triggering signals and reverse-bias signals are applied to the gate of the thyristor.

Abstract: A frequency converter having a silicon controlled rectifier comprises a protection circuit which includes a series resonant circuit connected in parallel with the silicon controlled rectifier to generate a reverse voltage thereacross in response to a short circuit established in response to a commutation failure of the silicon controlled rectifier. An inhibit circuit is provided to respond to the reverse voltage by inhibiting the current flow through the silicon controlled rectifier to allow the same to restore to its locking state.

Abstract: In an induction heating cooking apparatus, the frequency of electromagnetic energy is varied in response to a desired power setting level within an allowable range and the duty cycle of the energy is varied in response to the setting level while the frequency is set at the lower limit of the allowable range. The combined effects of frequency and duty cycle controls permit the power to vary from as low as 50 watts to as high as 2 kilowatts.

Abstract: Induction heating apparatus using gate-controlled switching devices includes a zero crossing point detector for detecting the occurrence of each zero crossing point of high frequency energization current, and a timing circuit which provides timing action in response to the detected zero crossing point. The timing action is controlled by a power control circuit which detects the level of energy delivered to a load within a range from the inherent turn-off time of the gate-controlled switching devices to a desired value.

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: Electromagnetic coupling between a pan or utensil load to be heated by magnetic induction and a source of high frequency magnetic flux is sensed by detecting a current which is indicative of the electromagnetic coupling by means of a current transformer. The detected current is compared with a reference level. Intermittent generation of the magnetic flux is commenced when, for example, a small magnetic metal object is inadvertently placed as a load with the result that the detected current becomes lower than the reference level. This allows intermittent check for the presence and absence of the inadvertently placed load for subsequent cooking operations and minimization of the heat generated therein.

Abstract: A gate controlled thyrister (SCR) used for switching at high frequency for induction heating is supplied with a negative bias during an interval ranging from the point where the forward current reaches to zero to the time of reapplication of a subsequent gating signal. This provides high dv/dt (the rate of rise of anode voltage) capability and small turn off time to the device.