High-frequency heating apparatus

A high frequency heating apparatus for driving a magnetron, comprising:

• 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.

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 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.

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.