High-Frequency Heating Apparatus

• US 20090001073A1
• Filed: 10/15/2004
• Published: 01/01/2009
• Est. Priority Date: 10/16/2003
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Morikawa, Hisashi, Moriya, Hideaki, Sakai, Shinichi, Suenaga, Haruo, Shirokawa, Nobuo, Matsukura, Toyotsugu
• Granted Patent: US 9,357,591 B2
• Time in Patent Office: Days
• US Class Current: 219/721
• CPC Class Codes: H05B 6/681 Circuits comprising an inverter, a boost transformer and a magnetron
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Abstract

A resonance type high frequency heating apparatus comprising; a direct current power supply; a series connection circuit consisting of a pair of semiconductor switching elements connected in parallel to the direct current power supply; another series connection circuit having a primary coil of a leakage transformer and a capacitor connected to both ends of one of the pair of semiconductor switching elements; and a drive means for driving each of the pair of semiconductor switching elements; wherein a variable dead time preparation circuit is provided in the drive means, and the variable dead time preparation circuit enables dead time to remain constant at below a predetermined frequency and causes the dead time to increase sharply at a point above a predetermined frequency.

Claims

1. A high frequency heating apparatus for driving a magnetron, comprising,

a direct current power supply;

a series circuit comprising a pair of semiconductor switching elements; and

a resonance circuit connected with a primary coil of a leakage transformer and a capacitor;

in which the series circuit is connected to the direct current power supply in parallel, and, in an AC equivalent circuit, an end of the resonance circuit is connected to an intermediate point of one end of the series circuit and the other end is connected to an end of the direct current power supply, and further comprising,

a drive means for driving the respective semiconductor switching elements;

a rectifying means, which is connected to a secondary coil of the leakage transformer; and

a magnetron, which is connected to the rectifying means, wherein a variable dead time preparation circuit which allows a period for which respective semiconductor switching elements are simultaneously turned off to vary in response to the switching frequency is provided.

4. A high frequency heating apparatus according to any one of claims 1 through 3, wherein the variable dead time preparation circuit allows the dead time to increase in response to a rise in the switching frequency.

5. A high frequency heating apparatus according to claim 4, wherein the variable dead time preparation circuit allows the dead time to remain constant or to increase minutely below a predetermined switching frequency.

6. A high frequency heating apparatus according to claim 5, wherein the variable dead time preparation circuit allows dead time to increase sharply at a predetermined switching frequency or more.

7. A high frequency heating apparatus according to claim 5, wherein the constant value or the minutely increased value of the dead time is variable below a predetermined switching frequency.

8. A high frequency heating apparatus according to claim 6, wherein the sharply increased value of the dead time is variable above a predetermined switching frequency.

9. A high frequency heating apparatus according to claim 5 or 6, wherein a value of the predetermined switching frequency is variable.

10. A high frequency heating apparatus according to any one of claims 1 through 3, wherein the variable dead time preparation circuit allows the dead time to increase stepwise in response to a rise in the switching frequency.

11. A high frequency heating apparatus according to any one of claims 1 through 10, wherein the variable dead time preparation circuit prepares dead time based on plus or minus offset voltages which vary by a first slope in proportion to an increase in a switching frequency and further vary from a predetermined switching frequency by a second slope.

12. A high frequency heating apparatus according to any one of claims 1 through 11, wherein the variable dead time comprises:

a VCC power supply, a duty controlled power supply, a first current which varies in proportion to a switching frequency, a second current which flows from a predetermined frequency and varies in proportion to the switching frequency, a third current which is obtained by synthesizing the first and second currents and multiplying the result by a predetermined coefficient, and an upper and lower potential preparation means for preparing upper and lower potentials which are obtained by adding plus and minus offset potentials in proportion to the third current to the duty controlled power supply, wherein a dead time is prepared based on the upper and lower potentials.

13. A high frequency heating apparatus according to claim 12, wherein at least either voltage of the duty controlled power supply or the switching frequency varies so as to control input power or input current.

2. A high frequency heating apparatus for driving a magnetron, comprising,

a direct current power supply;

two sets of series circuits each consisting of a pair of semiconductor switching elements; and

a resonance circuit connected with a primary coil of a leakage transformer and a capacitor;

in which two sets of the series circuits are respectively connected to the direct current power supply in parallel, and an end of the resonance circuit is connected to an intermediate point of the one end of series circuits and the other end thereof is connected to an intermediate point of the other direct current power supply,

and further comprising,

a drive means for driving the respective semiconductor switching elements;

a rectifying means, which is connected to a secondary coil of the leakage transformer; and

a magnetron, which is connected to the rectifying means, wherein a variable dead time preparation circuit which allows a period for which respective semiconductor switching elements are simultaneously turned off to vary in response to the switching frequency is provided.

3. A high frequency heating apparatus for driving a magnetron, comprising,

a direct current power supply;

a series circuit consisting of a pair of semiconductor switching elements; and

a resonance circuit connected with a primary coil of a leakage transformer and a capacitor;

in which the series circuit is connected to the direct current power supply in parallel, and the resonance circuit is connected in parallel to one of the semiconductor switching elements, and further comprising,

a drive means for driving the respective semiconductor switching elements;

a rectifying means, which is connected to a secondary coil of the leakage transformer; and

a magnetron, which is connected to the rectifying means, wherein a variable dead time preparation circuit which allows a period for which respective semiconductor switching elements are simultaneously turned off to vary in response to the switching frequency is provided.

14. A high frequency heating apparatus for driving a magnetron, which is comprised of a frequency-controlled type resonance inverter circuit having at least an arm including semiconductor switching elements;

the high frequency heating apparatus further comprises a variable dead time preparation circuit, which allows a period for which the respective semiconductor switching elements are simultaneously turned off to vary in response to the switching frequency;

wherein, the variable dead time preparation circuit prepares a dead time based on the plus and minus offset voltages which vary by the first slope in proportion to an increase in the switching frequency and further vary from a predetermined switching frequency by the second slope.