Electric heating – Metal heating – Of cylinders
Patent
1984-11-21
1987-06-09
Leung, Philip H.
Electric heating
Metal heating
Of cylinders
363 98, 315243, 331 87, H05B 668
Patent
active
046721592
ABSTRACT:
In a power-line-operated electronic inverter-type power supply for the magnetron in a microwave oven, the unfiltered pulsed DC output of a full-wave rectifier is applied to a bridge inverter, the output of which is a 30 kHz squarewave voltage pulse-amplitude-modulated at 120 Hz. By way of a step-up voltage transformer, this 30 kHz output voltage is applied to a high-Q series-resonant L-C circuit. The Q-multiplied voltage developing across the tank capacitor of this L-C circuit is then rectified and filtered for 30 kHz ripple-voltage. The output resulting from this high-frequency rectification is a 120 Hz pulse-amplitude-modulated current-limited DC voltage suitable for direct application to the magnetron. The bridge inverter has to be triggered into oscillation; which oscillation ceases each time the magnitude of the inverter DC supply voltage decreases below a given threshold level. Under normal operation, for each cycle of the 120 Hz pulse-amplitude-modulated DC voltage that constitutes this DC supply voltage, the inverter starts and stops oscillation. Simple control means then permits the starting point of this oscillation to be phase-controlled in fashion similar to the way in which a Triac or an SCR can be phase-controlled. When the inverter power supply is operating under full power, due to the innate characteristics of the magnetron-loaded L-C series-resonant circuit, the power factor of the power drawn from the 60 Hz power line is nearly 100%.
REFERENCES:
patent: 3324377 (1967-06-01), Mills
patent: 3569855 (1971-03-01), Noda
patent: 3840810 (1974-10-01), Fritts
patent: 3961152 (1976-06-01), Staats
patent: 3973165 (1976-08-01), Hester
patent: 4060752 (1977-11-01), Walker
patent: 4257088 (1981-03-01), Nilssen
patent: 4277728 (1981-07-01), Stevens
patent: 4307353 (1981-12-01), Nilssen
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