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    • 5. 发明专利
    • FI57034C
    • 1980-05-12
    • FI253372
    • 1972-09-14
    • MATSUSHITA ELECTRIC IND CO LTD
    • AMAGAMI KEIZOMORI HAZIMEKOBAYASHI TAKAOKIUCHI MITSUYUKIOGINO YOSHIO
    • H02H7/122H02M5/45H02M7/515H02M7/523H05B6/06H05B5/08
    • 1370865 Inverting apparatus for induction heating MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 25 July 1972 [10 April 1972 (6)] 34778/72 Headings H2H and H2F An induction heating device such as a cooking apparatus comprises an inverter fed from an A.C. source by way of a full wave rectifier, the heating device being energized by the' output from the inverter, the inverter including a gatecontrolled semi-conductor device and being provided with protective devices to prevent damage thereto which would occur due to current surges at switch-on and to heavy overload currents. Induction heating apparatus comprises a heating coil 35 which co-operates with a cooking utensil 37, the heating coil 35 being energized by an inverter 27 which comprises an inductor 34 and a capacitor 33 forming a resonant circuit which is set into resonance by the firing of a thyristor 29 paralleled by a diode 30 oppositely connected. The inverter 27 is supplied from an A.C. source 20 by way of a main switch 22 and a full wave rectifier 21. Firing of the thyristor 29 is controlled by a pulse generator 38 which generates a train of pulses conditioned by a feed back signal derived by a detector 42 representing the output frequency of the inverter whereby the output frequency of the inverter can be maintained sufficiently constant whatever the output voltage of the rectifier 21. In order to protect the thyristor 29 from a heavy instantaneous current when the inverter is switched on such switching on is arranged to take place when the output voltage of the rectifier 21 is substantially zero. For this purpose a zero voltage switching device 40 is provided which includes a thyristor serially connected in the negative output line 26 of the rectifier. A delay circuit 41 is provided so as to ensure that no pulses are delivered by the pulse generator 38 until the voltage thereacross reaches a predetermined level. Should the current supplied to the load 37 tend to reach an excessive level, a circuit 43 is provided to prevent such an excess current. In other embodiments excessive currents are reduced by using a series connected resistor or a variable inductor in the circuit of the heating coil 35 and heavy initial current flow may be prevented by using a series resistor in the output of the rectifier 21 which resistor is short-circuited by means of a relay during normal operation. The zero-volt switching device 40 may be made responsive to a switch thermally responsive to the heat generated in the load 37. The system is furthermore designed so that the output frequency of the inverter 27 is dependent upon the type of utensil being used.