Energization circuit for a microwave oven

Details Energization circuit for a microwave oven Energization circuit for a microwave oven

1980-08-07

1982-03-23

Reynolds, B. A.

Electric heating

Metal heating

Of cylinders

219 1055C, 219505, 361 99, 361165, 3071414, 307135, 315104, 323908, H05B 668

Patent

active

043214479

ABSTRACT:
An energization circuit for a microwave oven employs a PTC thermistor to eliminate high transient current surges resulting from energization and deenergization of induction elements therein to provide circuit protection both during oven start and operation. The energization circuit comprises first and second parallel circuit portions for energizing a transformer used to energize a magnetron that produces microwave energy, the first circuit portion including a normally open start switch and a current limiting PTC thermistor coupled in series relation and the second circuit portion including a relay operated switch, a relay for operating the relay operated switch, and a relay circuit portion connected to the first circuit portion between the start switch and PTC thermistor for energizing the relay upon closure of the start switch and then through the PTC thermistor upon opening of the start switch. During start-up, power is briefly supplied to the magnetron through the PTC thermistor to reduce high current surge flow to the transformer until the relay operated switch closes and supplies full power to the transformer and thus to the magnetron. The relay first is energized directly through the start switch upon closure of the latter and then by reverse current flow through the PTC thermistor upon closing of the relay operated switch and opening of the start switch.

REFERENCES:
patent: 3017564 (1962-01-01), Barney
patent: 3392309 (1968-07-01), Hickman
patent: 3460126 (1969-08-01), Spofford et al.
patent: 3821594 (1974-06-01), Webb et al.
patent: 3842233 (1974-10-01), Lamb
patent: 4011427 (1977-03-01), Risman
U.S. Patent application Serial No. 177,777 filed Aug. 13, 1980.

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