Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Patent
1997-12-01
1999-04-13
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
361 93, 361115, H02H 500
Patent
active
058943960
ABSTRACT:
An inrush current protection circuit for preventing generation of inrush current when an AC voltage is intermittently applied to a load, and an application of the circuit to a microwave oven. A switch is interposed between a power source for supplying an AC signal and a load. A positive characteristic thermistor, which restricts a magnitude of a current applied to the load to a predetermined value even when an inrush current of over a predetermined magnitude is applied thereto, is interposed between the power source and the load and connected in parallel to the switch. A DC relay provides to the switch a signal for turning ON the switch which is energized by the DC signal provided from a rectifier after a delay time passes from the time that the AC signal is inputted to the rectifier and is turned OFF. The turned-ON switch is provided to a bypassing circuit of the positive characteristic thermistor, and the AC signal is supplied to the load through the positive characteristic thermistor for the predetermined delay time from the time that the AC signal is received, and is supplied to the load through the switch after the predetermined delay time passes, thereby effectively cutting off the inrush current generated during when a power is intermittently supplied. The inrush current protection circuit can be employed to a power source of a microwave oven to prevent the inrush current from be flowing into a high voltage transformer.
REFERENCES:
patent: 4798927 (1989-01-01), Kaminaka
patent: 4800329 (1989-01-01), Masaki
patent: 5250774 (1993-10-01), Lee
patent: 5625520 (1997-04-01), Lim
Daewoo Electronics Co. Ltd.
Gaffin Jeffrey A.
Jackson Stephen W.
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