Emergency lighting system

Claim 2

An emergency lighting system for use with an electric discharge lamp including a ballast and having terminals adapted to be connected across an AC line, comprising: a free running oscillator having a feedback circuit for sustaining oscillations, a semi-conductor switching device in said feedback circuit for enabling or inhibiting operation of said oscillator, a battery for supplying unidirectional energy to said oscillator, a first circuit for sensing AC line power across said terminals and for charging said battery, a second circuit connected to said first circuit including a capacitor adapted to be charged from said first circuit and to back bias said switching device and prevent conduction thereof and thereby inhibit operation of said oscillator, said capacitor being adapted to discharge upon failure of the AC power and being ineffective to back bias said switching device, whereby said semi-conductor device is rendered conductive and operation of said oscillator is enabled, and circuit means for connecting the output of said oscillator across the lamp and ballast.

Claim 3

The system of claim 1, wherein the time constant of said second circuit is selected to be substantially longer than a cycle of the AC power so that the charge on said capacitor is maintained at a sufficient value to back bias said semi-conductor device when AC line power is present.

Claim 4

The system of claim 1, wherein said emergency lighting system, said lamp and said ballast have a common housing.

Claim 5

The system of claim 1, wherein said sensing means includes a transformer connected across the AC line, a unidirectional conducting device in circuit with the secondary of said transformer and connected across said battery to provide a charging current thereto from the AC line.

Claim 6

The system of claim 1, further including circuit means connecting said battery to said semi-conductor device to forward bias said device upon discharge of said capacitor.

Claim 7

The system of claim 1, wherein said oscillator is of the type having a saturating core, a load winding and feedback windings on said core and a pair of semi-conductor switching devices providing circuit paths to said load winding and switched ON and OFF by the voltage developed across said feedback windings upon saturation of said core, and said semi-conductor device is in circuit with said feedback windings.

Claim 8

The system of claim 1, wherein said oscillator includes a transformer in its output circuit, the secondary of said transformer connected in series with a capacitor across the lamp.

Claim 9

The system of claim 1, wherein said semi-conductor device is a controlled rectifier having a gate electrode, said gate electrode being connected to the positive terminal of said battery to forward bias said device upon discharge of said capacitor.

Claim 10

A power-pack assembly connectable to an electric discharge lighting fixture having an enclosure provided with means for mounting an electric discharge lamp and containing a ballast and electrical connections for the lamp to function from an AC power supply, said assembly including AC line power sensing means, a battery, a charger for the battery, an inverter, and a switching circuit, all mounted within a casing of a size and shape for insertion into the enclosure of the lighting fixture, said assembly having connecting means for connecting it to the lamp, to the ballast and to the AC power supply, whereby the assembly supplements the fixture so that the lamp provides regular light when the AC power supply is available and continues fed by the battery automatically to provide emergency light when the AC power supply fails, said inverter comprising a free-running oscillator having a feedback circuit for sustaining oscillations, said switching circuit beIng connected in said feedback circuit and to sense the available AC power, said switching circuit being effective to open said feedback circuit and render said oscillator inoperative when the availability of AC power is sensed from the supply.

Claim 11

A power-pack assembly connectable to an electric discharge lighting fixture having an enclosure provided with means for mounting an electric discharge lamp and containing a ballast and electrical connections for the lamp to function from an AC power supply, said assembly including AC line power sensing means, a battery, a charger for the battery, an inverter, and a switching circuit, all mounted within a casing of a size and shape for insertion into the enclosure of the lighting fixture, said assembly having connecting means for connecting it to the lamp, to the ballast and to the AC power supply, whereby the assembly supplements the fixture so that the lamp provides regular light when the AC power supply is available and continues fed by the battery automatically to provide emergency light when the AC power supply fails, said inverter comprising a free-running oscillator having a feedback circuit for sustaining oscillations, said switching circuit beIng connected in said feedback circuit and to sense the available AC power, said switching circuit being effective to open said feedback circuit and render said oscillator inoperative when the availability of AC power is sensed from the supply.