Emergency lighting system

Claim 2

An emergency system for operating an electric load comprising, a pair of AC line voltage input terminals coupled to said load, a source of DC voltage, an oscillator with its output coupled to said load, a controlled switching device for selectively coupling said DC voltage source to the oscillator to provide the operating voltage for the oscillator, circuit means for sensing the AC voltage across said input terminals and including means coupled to the control electrode of said switching device to hold the switching device open when the AC voltage is present and to close the switching device in the absence of said AC voltage, and means including the DC voltage source and the switching device for supplying a bias voltage to said circuit sensing means of a magnitude and polarity to hold the switching device closed upon actuation thereof by the circuit sensing means and during the time the AC voltage is absent from the input terminals.

Claim 3

An emergency system as claimed in claim 1 wherein said circuit sensing means includes a second controlled switching device with a control electrode coupled to said DC voltage source via said first switching device so that a bias voltage is applied thereto when the first switching device is closed, means for coupling an output electrode of the second switching device to the control electrode of the first switching device, and means for effectively coupling the AC voltage at the input terminals to the control electrode of the second switching device.

Claim 4

An emergency system as claimed in claim 2 wherein said circuit sensing means further comprises, means for rectifying the AC voltage present at the input terminals, a capacitor with a charge circuit coupled to the rectifying means, and means for applying the capacitor voltage to the control electrode of the second switching device.

Claim 5

An emergency system as claimed in claim 3 wherein said DC voltage source comprises a battery coupled to said rectifying means to receive a charge current therefrom, said system further comprising means for sensing the rectified input voltage and responsive thereto for varying the charge current so as to maintain said current constant despite variations in the AC voltage.

Claim 6

An emergency system as claimed in claim 2 wherein said bias voltage supplying means comprises a voltage divider connected to the DC voltage source via the first switching device and having a tap point coupled to the control electrode of the second switching device and located on the divider so that at a predetermined lower level of the potential of the DC voltage source the second switching device will change state and thereby control the first switching device into its open condition thereby to inhibit the supply of bias voLtage and the oscillator operating voltage.

Claim 7

An emergency system as claimed in claim 5 wherein said DC voltage source comprises a battery and the load comprises an electric discharge lamp.

Claim 8

An emergency lighting system comprising, an electric discharge lamp, a ballast device, a pair of AC voltage input terminals coupled to said lamp via the ballast device, a battery, a rectifier connected between the input terminals and the battery to supply a DC charge current to the battery, a capacitor coupled to said rectifier to be charged thereby, an oscillator with its output coupled to said lamp, a first transistor with its emitter-collector path connected between the battery and a DC voltage supply line for the oscillator, a second transistor with an output electrode coupled to the base of the first transistor to control the current flow therein, a third transistor with its emitter-collector path in parallel with the base-emitter circuit of the second transistor, means for coupling the capacitor voltage to the base electrodes of the second and third transistors so as to drive the third transistor into saturation when the AC voltage is present to charge the capacitor, said second and first transistors then being held in cut-off by said third transistor whereby operation of the oscillator is inhibited for lack of a DC line supply voltage, a bias circuit for the base of the second transistor that is coupled to the battery via the emitter-collector path of the first transistor, and a discharge circuit for said capacitor adapted to discharge same upon a failure of the AC input voltage whereby, upon a given discharge of the capacitor, the third transistor reverts to the cut-off state to allow said second and first transistors to turn on and supply via the first transistor the DC operating voltage for the oscillator and a bias voltage for the base of the second transistor, said bias voltage being of a magnitude and polarity to hold said second and first transistors in conduction.

Claim 9

An emergency lighting system comprising, an electric discharge lamp, a ballast device, a pair of AC voltage input terminals coupled to said lamp via the ballast device, a battery, a rectifier connected between the input terminals and the battery to supply a DC charge current to the battery, a capacitor coupled to said rectifier to be charged thereby, an oscillator with its output coupled to said lamp, a first transistor with its emitter-collector path connected between the battery and a DC voltage supply line for the oscillator, a second transistor with an output electrode coupled to the base of the first transistor to control the current flow therein, a third transistor with its emitter-collector path in parallel with the base-emitter circuit of the second transistor, means for coupling the capacitor voltage to the base electrodes of the second and third transistors so as to drive the third transistor into saturation when the AC voltage is present to charge the capacitor, said second and first transistors then being held in cut-off by said third transistor whereby operation of the oscillator is inhibited for lack of a DC line supply voltage, a bias circuit for the base of the second transistor that is coupled to the battery via the emitter-collector path of the first transistor, and a discharge circuit for said capacitor adapted to discharge same upon a failure of the AC input voltage whereby, upon a given discharge of the capacitor, the third transistor reverts to the cut-off state to allow said second and first transistors to turn on and supply via the first transistor the DC operating voltage for the oscillator and a bias voltage for the base of the second transistor, said bias voltage being of a magnitude and polarity to hold said second and first transistors in conduction.

Claim 10

An emergency system as claimed in claim 1 wherein said circuit sensing means includes means responsive to the AC input voltage for holding the switching device open and for preventing said switching device from closing unless AC voltage is present at the input terminals and then subsequently is absent therefrom whereby operation of the oscillator is conditioned upon the appearance subsequent of the AC voltage at the input terminals.

Claim 11

An emergency system as claimed in claim 1 wherein said means coupled to the switching device control electrode comprises a device jointly controlled by the DC voltage source via said switching device and by the AC voltage at the input terminals for controlling the operation of the switching device so as to inhibit the start of oscillations of the oscillator unless the AC and DC voltages are both present.

Claim 12

An emergency system as claimed in claim 1 wherein said bias voltage supplying means includes an impedance element responsive to the DC voltage source in the closed condition of the switching device to apply a bias voltage to said circuit sensing means that is determined by the amplitude of the DC voltage.

Claim 13

An emergency system as claimed in claim 1 wherein said circuit sensing means comprises a second controlled switching device having a control electrode coupled to said bias voltage supplying means and an output electrode coupled to the control electrode of the first switching device, said DC voltage source comprises a battery, means coupled to said AC input terminals and said battery for applying a constant charge current to said battery, and means for coupling the AC voltage at the input terminals to the control electrode of the second switching device.

Claim 14

An emergency system as claimed in claim 11 further comprising indicator means coupled to said charge current applying means, and wherein said bias voltage supplying means includes an impedance element responsive to the DC voltage source in the cLosed condition of the switching device so that at a given voltage level of the DC voltage source the second switching device will change state and thereby operate the first switching device into its open condition to block the passage of the bias voltage and the oscillator operating voltage.