False failure prevention circuit in emergency ballast

摘要

A backup ballast used with a primary ballast for providing power to one or more lamps. The backup ballast includes an output switch and a delay circuit. The output switch has a first operating mode for connecting a primary power source via the primary ballast to a first set of the lamps and second operating mode for connecting a backup power source with a second set of the lamps. The output switch operates in the first operating mode when it is energized and in the second operating mode when said it is not energized. The delay circuit is adapted for connecting to the primary power source for receiving power therefrom. The delay circuit is connected to the output switch for energizing it while the power is being received and for a delay period thereafter. The delay circuit includes an energy-storage component for storing energy while the power is being received and discharging the stored energy when the power is not being received in order to energize the output switch for the delay period.