High frequency supply system for gas discharge lamps and electronic ballast therefor

Abstract

The invention is both a system for supplying high frequency alternating current to gas discharge lamps, such as fluuorescent lamps, and the like and a unit that can be placed in or adjacent to a lighting fixture to convert a direct current supply into high frequency AC and also provide the ballast needed for operation of the gas discharge lamps. This unit contains a symmetrical, class B, push-pull current-limited, tuned-collector, sinusoidal oscillator which is self starting, highly efficient and stable over a wide range of input voltage, with or without load. The number of parts is a minimum and the parts are relatively low cost, the power losses are very low and the system operates at high power factor with low acoustic and radio noise and low flicker. The system may derive the current from a commercially available source at any voltage and phase but preferably three phase primary of a building transformer can convert this into six phase at the output terminals which can be converted to DC of low ripple even without filtering. From the central building supply, it is possible to send AC at suitable voltage to subcenters in the building for rectification, inversion and use in lighting fixtures but preferably there is a single rectifier adjacent to the main transformer and the DC at proper voltage is distributed to the fixtures where the ballast unit is installed in a fixture to supply the lamps in it with the high frequency AC. However, one ballast unit can serve, in many instances, more lamps than a single fixture holds and it is necessary in such instances to supply the high frequency AC from one fixture to another and this can be done with only two wires. The invention also provides means for dimming the lights, for supplying heating current to lamp filaments at high voltage at the start and much reduced voltage after the arc has been struck in the lamps served by the ballast unit, and this reduction in filament current takes place automatically without switches, resistsors or other expensive and energy consuming means. The transformers used in the practice of the invention may also be used to supply the building with AC for customary appliances, incandescent lighting, and the like.

Having thus described and illustrated the invention, what is claimed is: 
     
       1. An electrical system for supplying a high frequency AC voltage to gas discharge lamps, said system comprising: (a) rectifier means for converting an AC voltage to a rectified DC voltage,   (b) inverter means having a pair of input terminals and a pair of output terminals, said inverter means coupled to the output of said rectifier means for converting said rectified DC voltage appearing across said pair of input terminals to a high frequency AC voltage across said pair of output terminals, said inverter means comprising: (1) oscillator means comprising first and second switching transistors, each of said transistors having a base, collector and emitter, the emitters of said transistors connected to one of said pair of input terminals,   (2) tuned circuit means, said tuned circuit means comprising a transformer having first and second series-connected inductive windings respectively connected to the output terminals and connected with the collectors of said transistors, a .[.feed back.]. .Iadd.feedback .Iaddend.winding connecting the bases of said transistors,   (3) inductor means connected between the other one of said pair of input terminals and a junction point intermediate said first and second inductive windings for limiting the current in the collectors of said first and second transistors during the time period of simultaneous conduction of said transistors, and   (4) capacitor means coupled between said junction point and said feedback winding for increasing the switching .Iadd.speed .Iaddend.of said first and second transistors by decreasing base current of the transistor that is turning off and increasing base current of the transistor that is turning on; and     (c) means coupling at least one gas discharge lamp to the pair of output terminals of said inverter means.   
     
     
       2. An electrical system for supplying a high frequency AC voltage to gas discharge lamps, said system comprising: (a) rectifier means for converting an AC voltage to a rectified DC voltage,   (b) inverter means having a pair of input terminals and a pair of output terminals, said inverter means coupled to the output of said rectifier means for converting said rectified DC voltage appearing across said pair of input terminals to a high frequency AC voltage across said pair of output terminals, said inverter means comprising: (1) oscillator means comprising first and second switching transistors, each of said transistors having a base, collector and emitter, the emitters of said transistors connected to one of said pair of input terminals,   (2) transformer means comprising a pair of primary windings connected in series between the collectors of said transistors, a first feedback loop winding connecting the bases of said first and second transistors, and a second feedback loop winding connected by way of a pair of forward diodes to the base of each of said transistors, and   (3) inductor means connected between the other one of said pair of input terminals and a junction point intermediate said pair of primary windings for limiting the collector current of said first and second transistors during the time period of simultaneous conduction of said transistors; and     (c) means coupling at least one gas discharge lamp to the pair of output terminals of said inverter means.   
     
     
       3. The system as claimed in claim 2 further comprising a combination of a third winding in series with a resistor, said third winding-resistor combination being connected between one of the input terminals and an intermediate point of said second feedback loop winding. .Iadd. 
     
     
       4.  A high frequency AC lighting system for gas discharge lamps comprising: a plurality of electrical fixtures for removably holding gas discharge lamps, each said fixture being distributed throughout an area which is to be lighted by said lamps;   one or more subcenters for receiving commercial AC power at available voltage and phase;   means at each said subcenter for rectifying said received AC power into DC power for distribution from said one or more subcenters to said plurality of lighting fixtures;   wiring means for distributing said DC power from said one or more subcenters to said fixtures; and   a plurality of inverting means for receiving said DC power at input terminals thereof and inverting said DC into high frequency AC at output terminals thereof, each of said inverting means being located at one of said fixtures, and being electrically connected at said output terminals to a plurality of said lamps, and each said inverting means comprising a semiconductor switching means in electrical connection with a transformer. .Iaddend. .Iadd.   
     
     
       5.  A system as set forth in claim 4 in which each said fixture comprises a ballast means electrically connected to said lamps held in said fixture, and in which each said inverting means is electrically connected to said ballast means of its own and a plurality of adjacent fixtures. .Iaddend. .Iadd.6. A system as set forth in claim 5 in which each said inverting means is connected to one or more ballast means of adjacent fixtures by 
     
     
        two load-carrying wires. .Iaddend. .Iadd.7.  A system as set forth in claims 5 or 6 in which said ballast means comprises an inductor. .Iaddend. .Iadd.8. A system as set forth in claims 5 or 6 in which said ballast means comprises a capacitor. .Iadd.9. A system as set forth in claims 5 or 6 in which said ballast means comprises an inductor and a capacitor. .Iaddend. .Iadd.10. A system as set forth in claims 5 or 6 in which each said inverter means further comprises a pair of transistors in push-pull 
     
     
        connection with a collector transformer. .Iaddend. .Iadd.11.  A system as set forth in claim 10 in which each said fixture holds at least one gas discharge lamp comprising one or more filaments, and in which each said inverter means further comprises heater windings on said transformer, said heater windings being adapted to make electrical connection with said filaments of one or more said lamps. .Iaddend. .Iadd.12. A system as set forth in claim 11 in which said means for electrically connecting said output terminals of said inverter means comprises a separate magnetic core transformer and wherein said heater windings derive induction from said separate magnetic core. .Iaddend. .Iadd.13. A system as set forth in claim 4 further comprising energy-saving transformer means for deriving lamp filament voltage from, and proportional to, lamp arc voltage so as to reduce lamp filament power after arc voltage drops as said lamps turn 
     
     
        fully on. .Iaddend. .Iadd.14.  A system as set forth in claim 4 in which each said fixture holds at least one of said gas discharge lamps and each lamp comprises a filament, and in which each said inverting means is situated in a first fixture and is electrically connected to a second fixture, said second fixture comprising transformer means for heating the filament of each lamp in said second fixture, and said second fixture further comprising ballast means for each lamp in said second fixture. .Iaddend. .Iadd.15. A system as set forth in claim 4 in which the DC is delivered to each said inverting means by a two-wire circuit. .Iaddend. .Iadd.16. A system as set forth in claim 4 in which the DC is delivered to each said inverting means by a balanced three-wire circuit. .Iaddend. 
     
     
        .Iadd.17.  A system as set forth in claim 4 further comprising voltage transforming means for inputting said AC power to said rectifying means, and said voltage transforming means also comprising means for transforming said commercial AC to proper voltage for conventional AC facilities comprising at least one of (a) single phase output terminals, (b) three phase output terminals, and (c) six phase output terminals. .Iaddend. 
     
     
        .Iadd.18.  A high frequency AC lighting system system for gas discharge lamps comprising: one or more subcenters for receiving commercial AC power at available voltage and phase;   means at said subcenter for rectifying said received AC power into DC power for distribution from said one or more subcenters;   a plurality of electrical fixtures for removably holding gas discharge lamps each comprising one or more filaments;   wiring means for distributing said DC power from said one or more subcenters to said fixtures;   inverting means associated with at least one said fixture, and receiving said DC power at input terminals thereof and inverting said DC into high frequency AC at output terminals thereof for connection to said lamp, said inverting means comprising a semiconductor switching means in electrical connection with a transformer; and   energy saving transformer means in parallel electrical connection across at least one said lamp, for deriving lamp filament voltage from, and proportional to, lamp arc voltage so as to reduce lamp filament power after arc voltage drops as said lamp turns fully on. .Iaddend.