Two relay switching circuit for fluorescent lighting controller

Abstract

In a fluorescent lighting controller, a switching circuit operates to selectively couple a bank of electronic ballasts to an AC power source (100-277 Volts, 50-60 Hertz). The switching circuit comprises a pair of relays, preferably connected in parallel, with one of such relays having a controllably conductive device, such as an electronic switch, and preferably a triac, connected in series therewith. With the relays open, an air gap isolates the power source and ballasts. In closing the relays in sequence, one relay provides a conductive path from the power source to the triac. After a suitable delay to allow the relay contacts to stabilize in the closed position, the triac is triggered to provide a conductive path from the power source to the ballasts, and a large current surge (as much as 300 amps) flow to the ballasts. After the current surge has subsided, the other relay is closed to provide a direct conductive path between the power source and ballasts. As a result of this arrangement, the switching circuit is low cost, compact and reliable over an extended period of time.

Dependencies are inferred from the claim text.