Induction heating apparatus with protective circuit arrangement
First Claim
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1. An induction heating apparatus comprising, in combination:
- a power supply circuit including a rectifier coupled to an alternating current power source for generating a full-wave rectified unfiltered unidirectional excitation potential;
an inverter circuit coupled to said rectifier and including an induction heating coil, a commutating capacitor receptive of the excitation potential and connected to said induction heating coil, a silicon controlled rectifier having a control electrode, and a diode connected in inverse parallel relationship therewith to drive said induction heating coil with periodic energization current;
a charge absorbing circuit including a charge absorbing capacitor and a semiconductive switching device for providing a conductive path, when energized, between said commutating capacitor and said charge absorbing capacitor so that a charge stored in said commutating capacitor can be discharged through said conductive path to said charge absorbing capacitor;
a circuit for timing energization of said charge absorbing circuit at a zero voltage point of the alternating current voltage of said power source by counting number of zero voltage points from that instant said power circuit is energized;
delay means for providing a delay interval from an instant a predetermined number of zero voltage points has been counted to allow said commutating capacitor to recharge to a predetermined level; and
a gating circuit means energized upon expiration of the delay interval, said gating circuit means being coupled to said control gate of said silicon controlled rectifier for rendering the same repetitiously conductive at a predetermined frequency.
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Abstract
An induction heating apparatus is provided with protective circuit arrangements which ensure against surge currents caused by inappropriately timed gating-on of a gate controlled rectifier or by erroneous use of a load material such as non-magnetic or ferro-magnetic material. The timed gating of the gate-controlled rectifier is accomplished by means of a delay circuit which serves to count timing after a rectified excitation potential drops to the zero voltage point. A coincidence circuit is provided to detect coincidence of two signals, one is a pulse having a predetermined width and the other is a signal derived when the periodic cycle of the energization currents departs from the predetermined cycle period.
27 Citations
4 Claims
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1. An induction heating apparatus comprising, in combination:
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a power supply circuit including a rectifier coupled to an alternating current power source for generating a full-wave rectified unfiltered unidirectional excitation potential; an inverter circuit coupled to said rectifier and including an induction heating coil, a commutating capacitor receptive of the excitation potential and connected to said induction heating coil, a silicon controlled rectifier having a control electrode, and a diode connected in inverse parallel relationship therewith to drive said induction heating coil with periodic energization current; a charge absorbing circuit including a charge absorbing capacitor and a semiconductive switching device for providing a conductive path, when energized, between said commutating capacitor and said charge absorbing capacitor so that a charge stored in said commutating capacitor can be discharged through said conductive path to said charge absorbing capacitor; a circuit for timing energization of said charge absorbing circuit at a zero voltage point of the alternating current voltage of said power source by counting number of zero voltage points from that instant said power circuit is energized; delay means for providing a delay interval from an instant a predetermined number of zero voltage points has been counted to allow said commutating capacitor to recharge to a predetermined level; and a gating circuit means energized upon expiration of the delay interval, said gating circuit means being coupled to said control gate of said silicon controlled rectifier for rendering the same repetitiously conductive at a predetermined frequency. - View Dependent Claims (2, 3, 4)
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Specification
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Current AssigneeMatsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
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Original AssigneeMatsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
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InventorsKobayashi, Takao, Ogino, Yoshio, Kiuchi, Mitsuyuki, Amagami, Keizo
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Primary Examiner(s)Reynolds, Bruce A.
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Application NumberUS05/596,203Time in Patent Office413 DaysField of Search219/10.49, 219/10.77, 219/10.75, 219/10.79, 321/18, 321/45, 321/43, 321/44, 321/14, 321/16, 307/240US Class Current219/668CPC Class CodesH02H 7/122 for inverters, i.e. dc/ac c...H02M 5/45 using semiconductor devices...H02M 7/523 with LC-resonance circuit i...H02M 7/525 with automatic control of o...H05B 3/683 Plates having their feeding...H05B 6/06 Control, e.g. of temperatur...
