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.

Description

INTRODUCTION

This application is a continuation-in-part of our prior application Ser. No. 161,914 filed June 23, 1980, now abandoned.

The present invention relates to an electrical system for supplying high frequency alternating current to gas discharge lamps. The system is adapted to be connected to commercially available alternating current supply lines, preferably a three-phase current supply. The system comprises means to rectify the alternating current to a relatively smooth direct current at a safe voltage for transmission over ordinary building wiring and electronic means to invert the direct current to high frequency alternating current, e.g. 20 to 30 KHZ, and suitable voltage adapted to supply gas discharge lamps, without or with filament heating means, and to control the current through the lamps. The invention also relates to said electronic means referred to herein as electronic or solid state ballast.

BACKGROUND OF THE INVENTION

It is well known to utilize high frequency (20 kHz or above) in the operation of fluorescent lamps for the purpose of eliminating standard 60 cycle noise and reducing power loss via lengthy transmissions within a relatively large building complex.

In the most common prior practice, 60 Hz single phase power has been distributed to be rectified at each fixture. In a large building this necessitates many rectifiers, and large, usually electrolytic, condensers or capacitors and perhaps large inductors. Inductors used for such purposes are inefficient, costly and noisy while electrolytic capacitors are unreliable, temperature sensitive and have limited lifetimes. Capacitor filters used alone lead to a very low power factor for the system and consequently to large power transmission losses.

Prior proposed systems to obtain the benefit of high frequency operation of the lamps by rectifying AC to provide DC to high frequency inverters and to operate at the necessary high power factor, high efficiency and low noise have either been prohibitively costly or have made unacceptable compromises in performance and reliability. No one has succeeded in providing a system which has found acceptance in the market place, which has been affordable, and has the advantages of the present, safe, economic, reliable, efficient and flexible system and ballast for operating at frequencies in the range of about 20 to 30 kHz or higher.

The present invention satisfies this long felt need.

SUMMARY OF THE INVENTION

The present invention comprises a system for supplying high frequency alternating current, preferably from a source of low frequency alternating current by rectifying means and inverting means, to a large number of gaseous discharge lamps, usually fluorescent lamps, e.g., fixtures for all the lamps in a large building, optionally with means for dimming the lamps, and electronic means frequently referred to herein as electronic or solid state ballast, for use in the system (a) for providing the necessary starting voltage for the lamps when the resistance to current flow is comparatively high, (b) for limiting the current flow in the lamp circuit during lamp operation when the resistance to current flow is comparatively low, and (c) for optionally supplying current to heat the filaments or electrodes in the lamps, preferably at a comparatively high level to start operation of the lamp and at a much lower level during operation.

The system comprises a distribution center in which there is usually a single central transformer adapted to be connected to the commercially available AC power source, preferably three-phase current, with its primary winding designed to accept the power from the supply at the line voltage, which is usually too high for safe distribution in the building, and with its secondary designed to supply the building distribution center with current at suitable building voltage. If the available current supply is at suitable voltage for distribution through the building, then a central transformer is not necessary. The building distribution system comprises a plurality of subcenters, e.g., one for each floor, if not too extensive an area, or several if the floor area is too extensive for a single subcenter to suffice for efficient distribution. From the subcenter the usual building needs may be supplied by means of a transformer having its primary designed for the voltage of distribution from the center and its secondary designed for connection to convenience outlets and the like (not shown) which usually are supplied by 110-130 volt lines. At the subcenter a rectifier is provided at strategic locations on the floor to convert the AC to DC to supply a plurality of inverters near the lamps. Preferably the transformer in the subcenter has its primary windings connected in delta configuration and its secondary windings connected in star or Y-configuration with the common connection serving as a terminal for a neutral or ground line. Preferably the secondary windings include not only the usual three windings but an additional three windings wound in the manner described hereinafter so as to supply six-phase current to the rectifiers. Six-phase current has a relatively small ripple which makes rectification to an almost smooth direct current relatively simple and inexpensive. The rectifier preferably comprises a six-phase diode bridge providing direct current as a positive and at a negative terminal for connection to positive and negative lines, which, with the natural or ground line mentioned above form a DC distribution system for supplying the inverters. There is an inverter for each fixture or group of adjacent fixtures, depending upon the number of lamps per fixture. The inverters of the invention are capable of supplying one to four or even a few more lamps without overloading. One skilled in the art can readily determine the number of lamps and fixtures to be supplied by each inverter from the ratings of the lamps and inverters.

The inverter includes means to convert the direct current it receives from the system described above into high frequency alternating current, e.g., 20 to 30 kHz, a transformer for this high frequency AC to convert the voltage generated in the conversion means into proper voltage to operate the lamps, and, if desired, to heat the filaments thereof. Means to smooth out the DC before it is converted to AC may be incorporated, if deemed necessary or desirable. Further, means to facilitate starting the lamps may be provided as well as means to limit the current flow through the lamps after they begin to conduct current. The inverter and associated means constitute the electronic or solid state ballast of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The invention, its features and advantages, will be described in conjunction with the several views of the drawings in which:

FIG. 1 is a block diagram of the system of the invention showing the commercial power source of three-phase current, a transformer for reducing the high supply voltage to a voltage suitable for distribution from the central transformer for the building to subcenters where the AC is rectified to DC, preferably a three wire transmission system, to supply a plurality of inverters which supply the desired high frequency power to operate the lamps;

FIG. 2 is a schematic diagram of the secondary of the transformer in the rectifier with associated parts to provide three-wire direct current for the inverters;

FIG. 3 represents the primary of the transformer of FIG. 2;

FIG. 4 represents an additional secondary for the transformer in the central power room or the transformer in the inverter to obtain single-phase AC for use in convenience outlets, for driving motors of air-conditioning equipment and the like;

FIG. 5 is a similar diagram to FIG. 4 showing means resister 54bdespicts depicts a circuit comprising an inverter like the inverter of FIG. 16 and an inverter output circuit. Components in the circuit of FIG. 19 have been given the same reference numbers as corresponsing corresponding parts in the circuit of FIG. 1161 16 with a postscript c. The output circuit of FIG. 19 includes three fluorescent lamps 264c, 265c and 266c, 264c and 265c being connected in series and then connected in parallel with lamp 265c across the terminals of secondary winding 249c of the inverter transformer 247c. The series connected lamps have a capacitor ballast 279c between the line connecting short winding 268c with filament 278c and the terminal of secondary winding 249c. The short windings 268c, 274c and 280c have voltage induced in them from primary 287 which receives voltage from winding 249c of the inverter transformer 247c. An auxiliary circuit 289 comprising in series a primary winding 290 of a saturable reactor 291 having a magnetic core, e.g., ferrite, and a resister resistor 293 connected to the DC terminals 241c and 242c. The secondary of reactor 291 is a short winding 294 having one terminal connected by line 295 to one terminal of inverter transformer 247c and by line 296 to a capacitor 297 connected to the line connecting short winding 268c with filament 278c, and to an inductor 298 on core 292 connected to the line connecting short winding 277c with filament 278c.

Ballast capacitor 279c and ballast inductor 284 conduct small currents to their respective lamps for very dim operation. Additional current flows through ballast capacitor 297 and ballast inductor 298 by way of the saturable reactor windings 294 for brighter operation. The amount of additional current is controlled by the DC current in winding 290 of the saturable reactor which DC current, in turn, is controlled manually or automatically by means of the variable resistor 293. In this manner, the light internsity intensity may be changed in response to varying needs.

The circuits of the invention, and in particular the electronic ballast circuits have great benefit to the utility industry because of its efficiency which make it possible to save capital investment. The invention has great value also to users of electric power for lighting because of great savings that can be made in consumption of electric power.

Fluorescent lamps operate more efficiently on high frequencies than they do on commercially available AC of 50 to 60 Hz., a fact that the art has recognized for many years, as the discussion of the prior art hereinabove states. Despite this recognition there is not available on the market either a system having the advantages of the present affordable, safe, economic, reliable, efficient and flexible system for operating at high frequencies, e.g., in the range of 20 to 30 kHz or higher, nor a ballast that combines safe, economic, reliable, efficient and flexible use in present fluorescent installations and particularly as part of a system powered from a three-phase source. The system and ballast of the invention make use of the enhanced efficiency allowed by high frequency in the range of 20 to 30 kHz, keep the power loss to a practical minimum in the inverter and ballast, keep the costs low, obtain high power factor (e.g., at least 90%), provide reliability by avoiding the use of components like electrolytic capacitors and by using a minimum number of parts, obtain low acoustic noise, low radio noise and low flicker.

The inverter may be described as a symmetrical, class B, push-pull, current-limited, turned-collector tuned-collector, sinusoidal oscillator. It is self starting, highly efficient and stable over a wide range of input voltage without squegging at any voltage, with or without load.

While the system and ballast have been described and illustrated with many modifications and embodiments, those skilled in the art will recognize that further modifications and embodiments may be made within the ambit of the disclosure and claims without departing from the principles of the invention disclosed.

Claims

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 feedback 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 speed 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.

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.

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. 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. 7. A system as set forth in claims 5 or 6 in which said ballast means comprises an inductor. 8. A system as set forth in claims 5 or 6 in which said ballast means comprises a capacitor. 9. A system as set forth in claims 5 or 6 in which said ballast means comprises an inductor and a capacitor. 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. 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. 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. 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. 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. 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. 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.

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.

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.