High-efficiency DC ballast arrangement with automatic polarity protection and emergency back-up for lighting fixture in a suspended DC-powered ceiling system

A ballast arrangement for a fluorescent lighting fixture mountable in different orientations in an opening bounded by frame elements in a grid framework of a suspended ceiling system having a DC power supply, comprising:

• a pair of DC input terminals connected to the DC power supply with a predetermined polarity in one orientation of the fixture, and with a reverse polarity in another orientation of the fixture;
• an automatic polarity protection circuit including a high-efficiency, DC-to-DC bridge connected to the DC input terminals for supplying an output DC voltage of constant polarity no matter in which of the orientations the fixture is mounted;
• a high-efficiency, DC-to-DC converter connected to the protection circuit for converting and reducing the output DC voltage to a reduced DC voltage;
• a main DC ballast circuit including a main DC ballast powered by the reduced DC voltage from the DC-to-DC converter to enable a lamp in the fixture to be illuminated during normal operation;
• a sensing circuit for sensing failure of the DC power supply;
• and
• an emergency back-up DC ballast circuit to enable the lamp in the fixture to be illuminated during emergency operation upon sensing the failure of the DC power supply by the sensing circuit, the emergency back-up DC ballast circuit including a battery charged to a charged DC voltage by the reduced DC voltage during the normal operation, and an emergency DC ballast powered by the charged DC voltage from the battery to enable the lamp in the fixture to be illuminated during the emergency operation.

In a suspended ceiling system having a DC power supply and a grid framework of frame elements lying in a ceiling plane and bounding a plurality of openings, a method of mounting and operating a lighting fixture mountable in different orientations in the system, the method comprising the steps of:

• mounting the lighting fixture in a selected one of the orientations in a selected one of the openings;
• connecting a pair of DC input terminals to the DC power supply with a predetermined polarity in one orientation of the fixture, and with a reverse polarity in another orientation of the fixture;
• connecting an automatic polarity protection circuit to the DC input terminals for supplying an output DC voltage of constant polarity no matter in which of the orientations the fixture is mounted;
• powering a main DC ballast circuit including a main DC ballast by the output DC voltage from the protection circuit to enable a lamp in the fixture to be illuminated during normal operation;
• and
• enabling the lamp in the fixture to be illuminated during emergency operation by an emergency back-up DC ballast circuit to upon failure of the DC power supply, including charging a battery to a charged DC voltage by the output DC voltage during the normal operation, and powering an emergency DC ballast by the charged DC voltage from the battery to enable the lamp in the fixture to be illuminated during the emergency operation.