Induction heating apparatus with means for improving the dv/dt capability of a silicon-controlled rectifier used therein
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorsMitsuyuki Kiuchi, Takumi Mizukawa
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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.
Claims4
The method of providing a high dv/dt capability of a silicon-controlled rectifier of a static power converter, wherein the dv/dt is the rate of rise of forward voltage applied to the anode of said silicon-controlled rectifier and wherein the control gate thereof is supplied with positive gating pulses at an ultrasonic frequency to generate a forward commutating current which drives an induction heating coil of an inverter at said ultrasonic frequency, comprising, detecting the cessation of said forward commutating current, setting a flip-flop device to an ON state upon the detection of the cessation of said forward commutating current, resetting said flip-flop device to the OFF state by said positive gating pulses, and applying a negative potential to the control gate of the silicon-controlled rectifier with respect to the cathode during the ON state of said flip-flop device.
An induction heating apparatus including a full wave rectifier to receive a alternating current voltage for generating a full-wave rectified unidirectional voltage, a power converter including a silicon-controlled rectifier adapted to be supplied with said unidirectional voltage, a feedback diode coupled in inverse parallel relation therewith, a commutating LC network including an induction heating coil coupled across said silicon-controlled rectifier, and a gate control circuit for repetitiously gating said silicon-controlled rectifier at ultrasonic frequency, said gate control circuit comprising means for generating positive gating pulses at ultrasonic frequency to initiate a forward commutating current flow through said silicon-controlled rectifier in one half cycle of said ultrasonic frequency and a backward commutating current flow through said feedback diode in the other half cycle, means for detecting said reverse commutating current flow, a bistable device having a first binary state in response to the detection of said reverse commutating current flow and a second binary state in response to said gating pulse, and a switching gate responsive to the first binary state of the bistable device to apply a negative potential from a DC voltage source to the control gate of said silicon-controlled rectifier with respect to the cathode thereof.
An induction heating apparatus comprising, a full wave rectifier to receive an alternating current voltage for generating a full-wave rectified unidirectional unfiltered voltage, a static power converter including a silicon-controlled rectifier supplied in operation with said unidirectional voltage, a feedback diode coupled in inverse parallel relation therewith, a commutating LC network including an induction heating coil coupled across main terminals of said silicon-controlled rectifier, means for generating first pulses at an ultrasonic frequency, means for generating second pulses in response to the leading edge of the first pulses and having a duration smaller than the duration of said first pulses, means for applying the second pulses to the control gate of the silicon-controlled rectifier to turn it on and off at said ultrasonic frequency to generate a forward commutating current through the main terminals of the silicon-controlled rectifier in the first half cycle of the ultrasonic frequency and a backward commutating current through the feedback diode in the second half cycle of the ultrasonic frequency, means for inverting the polarity of the first pulses, a switching gate responsive to said inverted pulses for coupling a negative potential from a DC voltage source to the control gate of said silicon-controlled rectifier with respect to the cathode thereof, and said first pulses having a duration equal to the duration of said forward commutating current.
Dependencies are inferred from the claim text.