Delayed turn-off switching circuit

Details Delayed turn-off switching circuit Delayed turn-off switching circuit

1977-06-03

1979-07-03

Smith, Alfred E.

Electric lamp and discharge devices: systems

Regulation of the control current and/or potential applied...

315307, 315362, 315DIG4, G05F 100, H05B 3702, H05B 3904, H05B 4136

Patent

active

041601920

ABSTRACT:
An electronic circuit for de-energizing a lamp or other load after a predetermined period of time uses a gate controlled switch, e.g., thyristor, connected between the load and a source of A.C. voltage. The gate of the thyristor receives control current through a capacitor across which is connected a manual switch. In order to maintain the lamp energized, the switch is closed, bypassing the capacitor, so that uninterrupted gate current flows into the thyristor gate terminal to maintain the thyristor on. The delayed turn-off function is provided by opening the manual switch, whereby the capacitor in the thyristor gate charges up at a rate determined by an RC time constant. The charge build-up on the capacitor decreases the magnitude of gate current until the thyristor turns off due to gate current starvation. Several different embodiments of the circuit are disclosed.

REFERENCES:
patent: 3732484 (1973-05-01), McKenna
RCA Technical Notes No. 715, Jun. 1967, "Triggerless Phase Control Circuit for Sensitive Gate Triacs", R. J. Buczynski.

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