US 4,074,101 AGranted

Induction heating apparatus using a pair of inversely parallel connected gate-controlled switching devices

AssigneeMatsushita Electric Industrial Co., Ltd.

InventorsMitsuyuki Kiuchi, Keizo Amagami, Takumi Mizukawa, Hideyuki Kominami

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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.

Claims23

Dependent claims

An induction heating apparatus comprising, a pair of input terminals connectable in use to a source of low frequency alternating voltage, at least a pair of first and second gate-controlled unidirectional conducting devices inversely parallel connected to the input terminals, means sensitive to the polarity of said alternating voltage for generating an output indicative of the polarity of the alternating voltage, means for gating on said first and second gate-controlled unidirectional conducting devices in succession at a high frequency in a given order in response to the output from said polarity sensitive means indicating one polarity of the alternating voltage and in succession at the high frequency in a reversed order in response to the output from said polarity sensitive means indicating the opposite polarity of the alternating voltage, and high-frequency commutating circuit means including an induction heating coil and a capacitor in series thereto responsive to a current produced when one of the gate-controlled conducting devices is gated on for producing in succession a commutating current that flows through said commutating circuit means and the subsequently gated-on gate-controlled conducting device in the opposite direction.

An induction heating apparatus comprising:

a first pair of inversely parallel connected first and second gate-controlled switching devices, a second pair of inversely parallel-connected third and fourth gate-controlled switching devices, the first and second pairs being connected in use in series to a source of low frequency alternating voltage, and wherein the first and third switching devices are poled in the same direction of conduction and the second and fourth switching devices are poled in the opposite direction of conduction;
means sensitive to the polarity of said alternating voltage for generating an output indicative of the polarity of the alternating voltage;
means for gating on said first, second, third and fourth switching devices in succession in a given order in response to the output from said polarity sensitive means indicating one of the polarity of the alternating voltage and in a reversed order in response to the output from said polarity sensitive means indicating the opposite polarity of the alternating voltage;
and
high frequency commutating circuit means including an induction heating coil and a commutating capacitor in series thereto responsive to a current produced when one of the gate-controlled switching devices is gated on for producing in succession a commutating current that flows through said commutating circuit means and a subsequently gated-on switching device.

2 more elements

Dependencies are inferred from the claim text.