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1. Apparatus for operating a discharge lamp from a battery, said lamp when operated displaying a negative volt-ampere characteristic, said apparatus comprising:
2. Apparatus for operating a fluorescent lamp from a battery, said lamp when operated displaying a negative volt-ampere characteristic, said apparatus comprising:
3. The apparatus as specified in claim 2, wherein said transistor-network switching means comprises two transistors, the collector of one of said transistors connects to the emitter of the other of said transistors and to said output terminal, the remaining collector and emitter of said transistors connect across said input terminals, and said driver secondary windings of said current transformers connect across the base and emitter
4. The apparatus as specified in claim 2, wherein said input terminals are connected to an AC main through a rectifier means and current limiting means to provide a DC supply for a trickle charging said battery when
5. The apparatus as specified in claim 4, wherein transistor-network inhibit means is connected to both said DC supply and to said transistor network means to energize said transistor network means when electrical
6. The apparatus as specified in claim 5, wherein said inhibit means comprises an inhibit circuit transistor having its base and emitter connected to said DC supply through current limiting means, the input portion of a diode bridge is connected to the emitter and collector of said inhibit circuit transistor, and the output portion of said diode bridge is connected to a shorting winding portion of said current transformer to render said transistor network means inoperative when electrical energy is available at said AC main.
BACKGROUND OF THE INVENTION
This invention relates to fluorescent lamp emergency lighting apparatus and, more particularly, to a very compact and efficient emergency lighting apparatus which will operate in a very positive and rapid fashion upon failure of the electrical power.
Standby emergency lighting apparatus is normally used in many public buildings, among other uses. Such apparatus normally comprises an incandescent lamp which is energized from a storage battery, with the battery being trickle charged when the normal electrical supply is not interrupted. An incandescent lamp is a relatively inefficient source of luminous energy as compared to a fluorescent lamp, and fluorescent lamp portable sources are known, such as described in U.S. Pat. No. 3,435,206, dated Mar. 25, 1969.
SUMMARY OF THE INVENTION
The present invention comprises an apparatus from operating a discharge lamp, such as a fluorescent lamp, from a battery. As is customary with discharge lamps, the fluorescent lamp, when operated, displays a negative volt-ampere characteristic. The apparatus comprises input terminals which are adapted to be connected across the battery and a low-impedance switching means is connected to the input terminals and is operable to develop square waves of voltage at output terminal means thereof. A series LC circuit is connected across the output terminal means of the switching means and one of the input terminals, and the lamp to be operated is adapted to be effectively connected in parallel with one of the inductive reactive portion and the capacitive reactance portion of the LC circuit. When the apparatus is initially energized, the applied alternating voltage initially develops a very high potential in order to strike or initiate operation of the lamp. After the operation of the lamp is initiated, the current through the lamp is constant for any given applied battery voltage because of the nature of the circuit, and the lamp current is independent of the negative resistance characteristics of the lamp. Thus the lamp will immediately strike and the circuit arrangement provides efficient ballasting for the lamp.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference may be had to the preferred embodiment, exemplary of the invention, shown in the accompanying drawings, in which:
FIG. 1 is a block diagram of the typical fluorescent lighting fixture of the present invention wherein all components are located within the unitized fixture; and
FIG. 2 is a circuit diagram for a fluorescent lighting apparatus constructed in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With specific reference to the form of the invention shown in the drawings, in FIG. 1 the confines of the fixture are represented by a dashed line. The fluorescent lamp is a conventional 20 watt lamp which is adapted to be energized by the ballasting and low-impedance switching network 12. This network in turn is operated from a sealed storage battery 14 which is maintained in a charged state by a battery charger 16. When the line voltage is not interrupted, the operation of the low-impedance switching network is maintained inoperative by the inhibit circuit 18. A conventional test button 20 is provided, as is a disconnect switch 22 which can be opened in order that the apparatus can be transported. Loss of the 120 volt line supply will remove the "inhibit" signal from the low-impedance switching network and the lamp will operate from the battery until the power supply is restored or the battery is totally discharged. Restoration of the 120 volt line supply at any time will render inoperative the ballasting and low-impedance switching network 12 through the inhibit circuit 18 and place the battery on charge. The battery charger may be a constant-rate trickle charger which is left on permanently, or a "taper-charge" device, or a "two-rate" charger, depending upon the requirements desired for speed of recharge.
With reference to the circuit diagram as shown in FIG. 2, when the 120 volts line supply is not interrupted, the sealed storage battery 14, which has an open circuit potential of 40 volts, for example, is trickle charged through D1, R1 and D2. The battery has input terminals 24 across which the low-impedance switching means comprising the transistors Q1 and Q2, and their associated circuitry, are adapted to be connected. When the 120 volt line supply is interrupted, the inhibit winding Ti no longer prevents the operation of the low-impedance switching means. Under these conditions, the flow of battery current to C2 is blocked by diode D2. The starting circuit C3, trigger diode D3 and R4 insures reliable starting, with C1 being kept discharged by R2 until Q1 fires. Upon starting, current initially flows through Q1, through the primary winding Tp of transformer T, then through C1 and L. Because of the low-impedance nature of the transistor switching network, square waves of voltage are developed at the output terminal means 26 of this network. This provides a sine wave of current and when the current passes through zero, Td1 turns Q1 "off" and Q2 is turned "on," and C1 discharges through Q2. There is thus formed a Boucherot constant current system for feeding the lamp 10 which is effectively connected across one of C1 or L. In the embodiment as shown, the lamp is effectively connected in autotransformer relationship across L although the lamp 10 could also be connected across C1.
By way of further explanation of the circuit, because of a low impedance, low voltage square waves which are applied to the resonant LC circuit, there is initially developed across the lamp 10 a very high potential such as in the order of 500 volts, which causes it to strike immediately. Thereafter, the current (IL) through the lamp 10 is equal to battery voltage (E) times a constant (K) times √C/L, i.e., IL = EK√C/L. Thus the fluorescent lamp which operates with a negative volt-ampere characteristic is automatically ballasted by the circuit combination and the current through the lamp 10 is constant for any given applied battery voltage and is independent of the negative resistance characteristics of the fluorescent lamp 10.
Further considering the foregoing circuit, the transformer T is a current transformer with one end of the primary winding Tp connected to the output terminal 26 of the transistor network and the other end of winding Tp is connected to the LC circuit. The transistor network in the embodiment as shown comprises two transistors, the collector of one of the transistors Q1 being connected to the emitter of transistor Q2 with the remaining collector and emitter of the transistors connected across the input terminals 24. The driver windings Td1 and Td2 of the current transformer T are connected across the base and emitter of each of the transistors Q1 and Q2.
In a preferred embodiment of the inhibit circuit 18, when the 120 volt line supply is "on," the transistor Q3 has its base and emitter connected across the DC supply through current limiting resistor R3. A diode bridge (DB) has its input connected across the collector and emitter of Q3 and its output connects to a shorting winding Ti which inhibits the operation of the switching network when the 120 volt line supply is "on."
A detailed description of each of the elements of the present apparatus is as follows:
Element Type __________________________________________________________________________ Q1 and Q2 PNP T1P30A 60V 1A Q3 PNP 2N2219A 40V 0.5A D1 and D2 1N5397 600V 0.4A D3 35 volt DB 4-1N536 50V 0.75A C1 0.168 mfd 600V C2 0.22 μfd 75V C3 0.1 mfd L 650 μH Lamp 20W F20T12 R1 1K 25 watt R2 56K R3 10K R4 47K Battery NiCd Sealed Cell __________________________________________________________________________
The foregoing transistor switching network will operate with a frequency of approximately 20 KHz. It should be understood that the operating frequency can be varied and because of the nature of the circuit, the effective ballasting of the lamp is independent of the negative volt-ampere operating characteristics of the lamp.
As an alternative embodiment, if the present circuit is utilized to operate a discharge lamp which has a relatively slow warm-up period, such as a high-pressure mercury-vapor lamp, the ballasting and switching network 12 can operate at all times with a sealed storage battery floated across the input of the switching network. Upon failure of the main power supply, the sealed storage battery will continue to operate the switching network and the lamp, and when the power is restored, the battery will be automatically recharged.
As another alternative embodiment, cathode heater windings wound on L can readily be provided for the fluorescent lamp 10, although for the intended application they are not needed since long lamp life is not a factor in an emergency lighting apparatus.