High-frequency heating apparatus
First Claim
1. A high frequency heating apparatus for driving a magnetron, comprising:
- a DC power supply;
a series circuit constituted by two pieces of semiconductor switching elements;
a resonant circuit in which a primary winding of a leakage transformer and a capacitor are connected, said series circuit being connected parallel to said DC power supply, and one end of said resonant circuit being connected to a center point of said series circuit and the other end of said resonant circuit being connected to one end of said DC power supply in an AC equivalent circuit;
driving means for driving said semiconductor switching elements respectively;
rectifying means connected to a secondary winding of said leakage transformer;
the magnetron connected to said rectifying means; and
a variable dead time forming circuit for varying a dead time during which said respective semiconductor switching elements are simultaneously turned OFF in response to a switching frequency,wherein a limitation is provided under which said dead time is not further widened when the switching frequency is increased.
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Accused Products
Abstract
A purpose of the present invention is to provide an inverter circuit capable of firmly turning ON IGBTs under limited condition, while a heat loss and noise can be hardly produced in semiconductor switching elements.
In a resonant type high frequency heating apparatus which is arranged by employing a DC power supply; a series connection circuit constructed of two semiconductor switching elements which are connected to the DC power supply; another series connection circuit constituted by a capacitor and a primary winding of a leakage transformer connected to both the terminals of one of the two semiconductor switching elements; and a driving means for driving the respective semiconductor switching elements respectively, a variable dead time forming circuit is provided in the driving means, while the variable dead time forming circuit makes a dead time constant at a switching frequency lower than, or equal to a predetermined switching frequency, and also, rapidly increases a dead time at a switching frequency higher than, or equal to the predetermined switching frequency. Furthermore, when the switching frequency becomes high, a limitation is provided by which the dead time is not further widened.
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Citations
14 Claims
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1. A high frequency heating apparatus for driving a magnetron, comprising:
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a DC power supply; a series circuit constituted by two pieces of semiconductor switching elements; a resonant circuit in which a primary winding of a leakage transformer and a capacitor are connected, said series circuit being connected parallel to said DC power supply, and one end of said resonant circuit being connected to a center point of said series circuit and the other end of said resonant circuit being connected to one end of said DC power supply in an AC equivalent circuit; driving means for driving said semiconductor switching elements respectively; rectifying means connected to a secondary winding of said leakage transformer; the magnetron connected to said rectifying means; and a variable dead time forming circuit for varying a dead time during which said respective semiconductor switching elements are simultaneously turned OFF in response to a switching frequency, wherein a limitation is provided under which said dead time is not further widened when the switching frequency is increased. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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2. A high frequency heating apparatus for driving a magnetron, comprising:
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a DC power supply; two sets of series circuits, each of said series circuits being constituted by two pieces of semiconductor switching elements; a resonant circuit in which a primary winding of a leakage transformer and a capacitor are connected, said two sets of series circuits being connected parallel to said DC power supply respectively, and one end of said resonant circuit being connected to a center point of said one series circuit and the other end of said resonant circuit being connected to a center point of the other series circuit; driving means for driving said semiconductor switching elements respectively; rectifying means connected to a secondary winding of said leakage transformer; the magnetron connected to said rectifying means; and a variable dead time forming circuit for varying a dead time during which said respective semiconductor switching elements are simultaneously turned OFF in response to a switching frequency, wherein a limitation is provided under which said dead time is not further widened when the switching frequency is increased.
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3. A high frequency heating apparatus for driving a magnetron, comprising:
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a DC power supply; a series circuit constituted by two pieces of semiconductor switching elements; a resonant circuit in which a primary winding of a leakage transformer and a capacitor are connected, said series circuit being connected parallel to said DC power supply, and said resonant circuit being connected to one of said semiconductor switching elements in a parallel manner; driving means for driving said semiconductor switching elements respectively; rectifying means connected to a secondary winding of said leakage transformer; and the magnetron connected to said rectifying means; and a variable dead time forming circuit for varying a dead time during which said respective semiconductor switching elements are simultaneously turned OFF in response to a switching frequency, wherein a limitation is provided under which said dead time is not further widened when the switching frequency is increased.
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14. In a high frequency heating apparatus for driving a magnetron, which is arranged by a frequency control type resonant inverter circuit having at least one arm including a plurality of semiconductor switching elements;
- wherein;
said high frequency heating apparatus is further comprised of; a variable dead time forming circuit for varying a dead time during which said respective semiconductor switching elements are simultaneously turned OFF in response to a switching frequency; and
wherein;said variable dead time forming circuit forms the dead time based upon both a plus offset voltage and a minus offset voltage, which are changed in a first inclination which is directly proportional to an increase of the switching frequency, and also, which are changed in a second inclination from said predetermined switching frequency.
- wherein;
Specification