Magnetron power supply having in-rush current limiter

Claim 2

In a microwave oven which includes: an oven cavity for receiving food to be cooked; a door for providing access to said oven cavity; a magnetron for supplying microwave energy into said oven cavity; lamp means for illuminating said oven cavity with light; power supply means for said magnetron, said power supply means including a filament transformer having a primary winding and a low voltage secondary winding and circuit means connecting said secondary winding to said magnetron filaments; and power lines for providing power to said power supply means; the invention comprising in combination therewith; first circuit means for placing said primary winding and said lamp means electrically in a series circuit across said power lines, and switch means responsive to operation of said cavity door for interrupting said series circuit and placing each of said primary winding and said lamp means individually in parallel across said power lines.

Claim 3

The invention as defined in claim 1 wherein said lamp means comprises a light bulb having a tungsten filament.

Claim 4

The invention as defined in claim 1 wherein said switch means comprises an electromechanical relay, said relay including contact means for interrupting said series circuit of primary winding and lamp means and having additional contact means for connecting each of said primary winding and lamp means individually across said power lines.

Claim 5

The invention as defined in claim 3 further comprising an On-Off switch for completing a circuit between said oven power supply means and external power lines for initially preparing said series current path through said lamp means and said primary winding.

Claim 6

In a microwave oven which includes: an oven cavity for receiving food to be cooked; lamp means for illuminating said oven cavity, said lamp means having an electrically resistive filament; a magnetron for supplying microwave energy into said oven cavity, said magnetron having a directly heated cathode construction and a filament; magnetron power supply means, said magnetron power supply means including a filament transformer having a primary winding and a secondary winding and circuit means connecting said secondary winding to said magnetron filaments; power line means for supplying power at a predetermined voltage to said magnetron power supply means; the invention comprising in combination therewith: first circuit means for placing said primary winding and said lamp means electrically in a series circuit across said power lines and switch means responsive to operation of said cavity door for interrupting said series circuit and placing each of said primary winding and said lamp means in parallel across said power lines.

Claim 7

In a microwave oven which includes: an oven cavity for receiving food to be cooked; lamp means for illuminating said oven cavity, said lamp means having an electrically resistive filament; a magnetron for supplying microwave energy into said oven cavity, said magnetron having a directly heated cathode construction and a filament; magnetron power supply means, said magnetron power supply means including a filament transformer having a primary winding and a secondary winding and circuit means connecting said secondary winding to said magnetron filaments; power line means for supplying power at a predetermined voltage to said magnetron power supply means; the invention comprising in combination therewith: first circuit means for placing said primary winding and said lamp means electrically in a series circuit across said power lines and switch means responsive to operation of said cavity door for interrupting said series circuit and placing each of said primary winding and said lamp means in parallel across said power lines.

Claim 8

A microwave oven including: an oven cAvity; a movable door for permitting access to said cavity; lamp means for illuminating said cavity; said lamp means having a tungsten filament; a magnetron for generating microwave energy for transmission into said oven cavity, said magnetron containing a directly heated cathode structure and heater terminals; power supply means for said magnetron, said power supply means including a filament transformer, said filament transformer having a primary winding containing first and second terminals and a low voltage secondary winding; means connecting said secondary winding of said transformer to said heater terminals of said magnetron; power circuit means for supplying line voltage to said power supply means, said circuit means applying said line voltage across first and second terminals; first On-Off switch means in series circuit with said power circuit means for completing a circuit to said first and second terminals; electromagnetic relay means, said relay means including a first set of normally open contacts, a second set of transfer contacts, and a third set of transfer contacts, each of said sets of transfer contacts including a break contact, a make contact and a transfer contact, said transfer contact normally maintains closed a circuit to said break contact and which upon energization of said relay interrupts said closed circuit and closes a normally open circuit to said make contact; door switch means connected in a series circuit, said relay means between said first and second terminals for energizing said relay means upon operation of said oven door; means connecting together in circuit, said break contacts of each of said first and second sets of relay contacts; means connecting said primary winding in circuit between said transfer contact of said first set and said first terminal of said power circuit means; means connecting said lamp means in circuit between said transfer contact of said second set and said second terminal of said power circuit means to form a series circuit with said primary winding and said lamp means; and means connecting said make contact of each of said second and first sets of relay contacts in circuit with said first terminal and said second terminal, respectively, of said power circuit means; and means connecting said first normally open contacts in circuit with said relay means and said power circuit means for maintaining said relay means energized independent of said door switch, subsequent to initial operation of said door switch; whereby upon closure of said On-Off switch current flows through said primary windings and said lamp means to provide reduced low voltage to said magnetron filaments and illuminate said oven cavity and whereby upon initial operation of said oven door said relay means operates and is maintained energized and places each of said lamp means and said primary winding individually across said power lines to fully illuminate said oven cavity and provide full heater voltage to said magnetron.

Claim 9

A microwave oven including: an oven cAvity; a movable door for permitting access to said cavity; lamp means for illuminating said cavity; said lamp means having a tungsten filament; a magnetron for generating microwave energy for transmission into said oven cavity, said magnetron containing a directly heated cathode structure and heater terminals; power supply means for said magnetron, said power supply means including a filament transformer, said filament transformer having a primary winding containing first and second terminals and a low voltage secondary winding; means connecting said secondary winding of said transformer to said heater terminals of said magnetron; power circuit means for supplying line voltage to said power supply means, said circuit means applying said line voltage across first and second terminals; first On-Off switch means in series circuit with said power circuit means for completing a circuit to said first and second terminals; electromagnetic relay means, said relay means including a first set of normally open contacts, a second set of transfer contacts, and a third set of transfer contacts, each of said sets of transfer contacts including a break contact, a make contact and a transfer contact, said transfer contact normally maintains closed a circuit to said break contact and which upon energization of said relay interrupts said closed circuit and closes a normally open circuit to said make contact; door switch means connected in a series circuit, said relay means between said first and second terminals for energizing said relay means upon operation of said oven door; means connecting together in circuit, said break contacts of each of said first and second sets of relay contacts; means connecting said primary winding in circuit between said transfer contact of said first set and said first terminal of said power circuit means; means connecting said lamp means in circuit between said transfer contact of said second set and said second terminal of said power circuit means to form a series circuit with said primary winding and said lamp means; and means connecting said make contact of each of said second and first sets of relay contacts in circuit with said first terminal and said second terminal, respectively, of said power circuit means; and means connecting said first normally open contacts in circuit with said relay means and said power circuit means for maintaining said relay means energized independent of said door switch, subsequent to initial operation of said door switch; whereby upon closure of said On-Off switch current flows through said primary windings and said lamp means to provide reduced low voltage to said magnetron filaments and illuminate said oven cavity and whereby upon initial operation of said oven door said relay means operates and is maintained energized and places each of said lamp means and said primary winding individually across said power lines to fully illuminate said oven cavity and provide full heater voltage to said magnetron.

Claim 10

The invention as defined in claim 6 wherein said magnetron heater is rated to consume normally a predetermined X watts of energy and wherein said line voltage from said power circuit means is a predetermined Y volts, and wherein said lamp means has a voltage rating of Y volts and a nominal power consumption rating within the range of 30 percent to 65 percent of said X watts.

Claim 11

The invention as defined in claim 5 wherein said magnetron filament is rated at a nominal predetermined power consumption of X watts and wherein said power line means supplies a voltage of Y volts and wherein said lamp means has a voltage rating of Y volts and a power consumption rating in the range of 30 percent to 65 percent of said X watts.