EP0134207A1 - Electronic ballast and lighting system utilizing it - Google Patents

Abstract

Electronic ballast for gas discharge lamps, in particular fluorescent tubes, which supply them with alternating current at high frequency and at an appropriate voltage from a direct current supply, such as a battery, a solar cell or a rectifier intended to be connected to a commercial source of alternating current at any voltage, frequency and phase. The ballast is intended to be used in combination with an electrical system, for example the electrical system of a building, provided with many members of electrical connections, such as fixings of fluorescent tubes, members of commercial distribution of frequency for an alternating current at a voltage suitable for devices, small motors etc., and the high frequency alternating current distribution system connecting the direct current source to one or more ballasts to supply the tubes intended for use in the fasteners. The ballast comprises an inverting member (40) comprising two symmetrical push-pull oscillators of class B and limited in current and preferably also not only a high frequency transformer (54) applying the output of the oscillator to the building wiring system , but also an additional transformer, for example an auto-transformer (130), the primary winding of which is placed between the terminals of a lamp (132) and having at least one secondary winding providing the heating current for the filaments ( 134, 136) fluorescent tubes.

Description

ELECTRONIC BALLAST AND LIGHTING SYSTEM UTILIZING IT

INTRODUCTION

The present invention in its most comprehensive embodiment 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 in its least comprehensive • embodiment relates to said electronic means referred to herein as electronic or solid state ballast.

BACKGROUND OF THE INVENTION Proposals to operate fluorescent lamps at frequencies higher than the commercially available 50 to 60 Hz alternating current have been made heretofore with claims for better energy efficiency than when operated in the usual manner at the commercially available frequency. Among advantages foreseen for higher frequencies was the possibility of employing smaller, lighter weight and lower cost fluorescent accessories because, while a great many improvements have been made in ballasts and other accessories designed for 60 cycle operation since fluorescent lamps were first placed on the market, the components of the control circuit such as transformers, reactors and capacitors reach a limit as to size and weight at any given frequency and in general, the higher the frequency the lower this limit becomes. The use of higher frequencies at first, however, involved a number of problems among which were the high cost and comparatively low

SUBSTITUTE SHEET efficiency of commercially available conversion equipment. Some subsequent developments indicated that sufficient improvement in frequency conversion was being made to make more general use possible. Control devices and circuits for use at higher frequencies were suggested for use in special applications and for possible general use.

The potential advantages of operating fluorescent lamps at frequencies above 60 cycles per second were thus generally recognized among skilled workers in this field, largely based on experimental work and on a few installations in special situations by the end of the 1960 decade. The realization of the envisioned benefits of higher frequency operation of fluorescent lamps awaited the development of circuits, systems and converting equipment that would be satisfactory both from the standpoint of efficiency and dependability on the one hand and cost on the other.

The need for alternating current at frequencies well above 3000 cycles, which was felt in fields other that fluorescent lamp lighting, motivated researchers to investigate the transistor as a possible tool to fill the need. Success in the development of circuits based on transistors for inverting DC to AC at high frequencies for use in these other fields motivated the development of circuits based on transistors for use with fluorescent lamps. The transistor made solid state fluorescent ballasts possible and by 1976 a solid state ballast was described comprising a 20-kHz sine-wave oscillator operating from 120 V single-phase AC with a diode bridge rectifier and a filter to generate a 170 V DC circuit supply. The basic circuit was essentially a Class C sine wave oscillator with an added filter choke to insure more efficient transistor switching. Two specific

UBSTITUTE SHEET applications for the basic circuit were proposed, one especially for 40 rapid-start fluorescent bulbs and the other for higher starting voltages required by most 96-inch instant start fluorescent lamps. The circuit was small and about 90% efficient and it was predicted that it "will probably become the 'standard' for all arc-lamp ballast work in the future." The prediction has not come to pass in the almost six (6) year intervening period.

The circuits to supply AC to solid state rectifiers referred to herein have included single-phase and three-phase supply lines. A three-phase supply has advantages over a single-phase supply, particularly in producing a relatively smoother DC after recti ication.

One element in a preferred rectifying circuit- of the invention comprises a known rectifier previously described as a 6-anode mercury arc rectifier supplied by a delta-star-connected transformer with the neutral of the six secondary windings connected to the cathode through a load and smoothing inductance.

Some proposed systems have suggested a centrally located inverter to supply high frequency power over a distribution system to a large number of lamps, e.g., to all the lamps in a large building. These systems have not succeeded in the market place for a number of reasons. One is that failure of the central inverter, which is necessarily large and complicated, results in serious inconvenience in the lighted area before repair of the specialized equipment can be accomplished. High frequency power distribution over a considerable distance introduces additional power losses. Acoustic noise at audio frequencies and radio noise radiated from long lines at higher frequencies are further problems. In addition, the wiring arrangement for such a system is complex and difficult to arrange when "rapid start" lamps are used because the

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SUBSTITUTE SHEET ^NATIO^ filaments of these lamps must be supplied with current to heat them and if the current for the filaments is distributed also from a central point as well as the high frequency current, the wiring costs are increased many times.

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. o one has■succeeded in providing a system which has found acceptance in the market place and which has an affordable, safe, economic, reliable, efficient and flexible ballast and system 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 in its most comprehensive embodiment comprises a system for supplying high frequency AC, preferably from a source of low frequency AC which includes rectifying means to convert the AC to DC and inverting means to convert DC to high frequency AC. The inverting means may supply one, a few, or a

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SUBSTITUTE SHEET ^ ATIOΦ large number of gaseous discharge lamps, usually flourescent lamps, e.g., all the flourescent lamps in a large building, optionally with means for dimming the lamps.

In its less comprehensive embodiment, the invention comprises 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 preferably 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

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SUBSTITUTE SHEET ^∑^1 outlets and the like which usually are suppplied by 110-260 volt lines. At a strategically located subcenter a rectifier is provided 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 the secondary in star configuration with the common center connection of the windings 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, when rectified, has a relatively small ripple which makes rectification to an almost smooth direct current relatively simple and inexpensive. The rectifier preferably comprises two six-phase diode groups providing direct current at a positive and at a negative terminal for connection to positive and negative lines, which, with the neutral or ground line mentioned above, form a DC distribution system for supplying the inverters. There is an inverter as an element in the electronic ballast 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 ballast from the ratings of the lamps and inverters.

The ballast includes inverter means to convert the DC it receives from the system described above into high frequency AC e.g., 20 to 30 kHz, a transformer for this high frequency AC to convert the voltage generated in the inverter means into proper voltage to operate the lamps, and, if desired, to heat the

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SUBSTITUTE SHEET _lOi 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 drawing in which:

FIG. 1 is a block diagram of the preferred system of the invention showing the commercial power source of three-phase current, a central transformer for the building which may be located in a central power room for reducing the high supply voltage to a voltage suitable for distribution from the central transformer to subcenters where the AC is rectified to DC, preferably a three- wire DC 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 windings of the transformer, e.g., in the rectifier, with associated parts to provide three-wire direct current for the inverters;

FIG. 3 represents one embodiment of a suitable primary, the transformer of FIG. 2;

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

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SUBSTITUTE SHEET *Z ti& FIG. 5 is a schematic diagram similar to FIG. 4 showing means to obtain single-phase current at 120/240 volts;

FIG. 6 is a circuit diagram of an inverter circuit suitable for use as an electronic ballast in the system of FIG. 1;

FIG. 7 shows a circuit diagram of a portion of a transistorized inverter of the prior art;

FIG. 8 is a modification of a portion of the circuit of FIG. 6 showing how to operate multiple rapid start fluorescent lamps in series;

FIG. 9 is circuit diagram of a portion of the circuit of FIG. 6 modified to provide for flashing of fluorescent lamps;

FIG. 10 illustrates a further modification of a portion of the circuit of FIG. 6 to provide means to reduce the power supplied to the electrodes of the lamps after starting;

FIG. 11A is a diagram of a circuit which supplies filament heating current to both filaments or electrodes of a fluorescent lamp at two levels, (1) full heating current at the start of operation of the lamp and (2) greatly reduced filament current, e.g., about one-third of the normal filament power, during operation of the lamps;

FIG. 11B is a diagram of the right portion of FIG. 11A modified to supply constant heating power to the filaments of the lamp;

FIG. 11C is a further modification of the right portion of FIG. 11A to achieve the same result but with slightly different connections to the transformer;

SUBSTITUTE SHEET FIG. 12 illustrates ways for connecting a plurality of lamps across the high-frequency, high-voltage lines from an inverter using both capacitor and inductor ballasts so as to obtain a favorable power factor in the high frequency supply lines;

FIG. 13 is a circuit diagram of an inverter circuit similar to the embodiment illustrated in FIG. 6 but with modified means to supply current to the bases of the two transistors and an alternative connection of the Zener diode in the circuit.

FIG. 14 is a diagram of the circuit connecting the inverter to two pairs of series connected fluorescent lamps with means for heating the filaments of all lamps and utilizing both capacitor and inductor ballasts for high power factor at the inverter output.

FIG. 15 is a diagram of the connection of the inverter to a plurality of lamps, two of the lamps being in series and the pair being connected in parallel with a single lamp across the lines from the high-frequency, high-voltage secondary of the transformer and including a saturable reactor for dimming lamps. DETAILED DESCRIPTION OF THE INVENTION

As stated in the summary of the invention above, the present invention in its most comprehensive embodiment comprises a system for supplying high-frequency AC to a plurality of fixtures for gaseous discharge lamps, usually fluorescent lamps. The preferred system will now be described which is adapted to receive low-frequency (50 to 60 Hz) AC from a commercially available source at whatever voltage the source happens to provide, transform it, if necessary, to a voltage suitable for distribution and transmitting it to rectifying means which produces a three-wire DC circuit which supplies power to the inverting means for converting the DC into high-frequency, high-voltage AC. Each

SUBSTITUTE SHEET ' ^OMPI Zno inverter supplies the high-frequency (20 to 30 kHz or higher) current to at least one fixture adapted to hold at least one fluorescent lamp. The fixture wiring connects the filaments or electrodes of the lamps to the high-frequency, high-voltage lines from the inverter. The invention is not limited to this preferred embodiment, however, but contemplates a system which derives the current for operating lamps in the fixtures of the circuit of the invention from a DC source instead of, or as an emergency adjunct to, the AC source mentioned above, as will be described in greater particularity hereinafter.

THE PREFERRED SYSTEM Referring first to FIG. 1, the system obtains its power from a commercially available source (not shown) to which connection is made by terminals la, lb and lc of the primary of a transformer 2. In most countries of the world commercially sold power is generated and transmitted as low-frequency (50 to 60 Hz) alternating current and, in order to minimize I R losses in transmission, the voltage in the generator is stepped up by transformers to a much higher voltage than the output of the generator and then stepped down, usually in a succession of voltage reductions, to voltages deemed safe for the various parts of the transmission system from the main transmission line to the entrance to the customer's premises. Sometimes this supply voltage is in the 110 to 240 volt range, which is considered a safe voltage for distribution in a building occupied by humans, such as a home, barn, shop, store, church, place of entertainment, etc. In many cases, particularly in recent years, the power is brought to the customer's premises at a much higher voltage, especially where the building to be supplied is a church, a school, a commercial structure, or the like. It is usual practice in such cases to

^SUBSTITUTE SHEET provide in the building a central transformer room to house the transformer necessary to reduce the supplied voltage to a voltage suitable for the building through which it will be distributed. Transformer 2 represents such a central transformer and its primary winding would be insulated to operate safely at the high supply voltage. The secondary winding would have the right number of turns in relation to the number of turns in the primary winding to step the voltage down to the building distribution voltage and make it available for connection to the building distribution system by output leads or terminals 3a, 3b and 3c. The primary windings for a three-phase circuit may be connected delta or Y, as the windings of the secondary may also be connected.

The building distribution system shown is a three-wire circuit from the transformer 2 and it is represented by lines 4, 5 and 6 which are connected to the secondary terminals 3a, 3b and 3c.

The lines 4, 5 and 6 are connected to a plurality of rectifying means 7 at subcenters in the distribution system. Four such rectifying means are illustrated in FIG. 1 by way of example and they are designated as 7a, 7b, 7c and 7d for ease of reference in FIG. 1 but the general designation 7 is used in the following description thereof. In general, each floor of a large building would have at least one subcenter and if the floor area is larger than a single subcenter can efficiently supply, a floor might have two or more subcenters at strategic locations.

If commercial power is available at the premises of a building at suitable building voltage, transformer 2 would not be necessary and the building distribution system would then start with lines 4, 5 and 6 which would connect directly to the source of power but there still would be a need for a building center to

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SUBSTITUTE SHEET ^V^*NATI^O*>^> receive the power and distribute it to the lines going to the subcenters.

Each rectifying means 7 receives the low-frequency alternating current at the building voltage on its input or primary side and delivers the power from its output or secondary side, preferably as three-wire direct current to lines 8, 9 and 10.

Referring now to FIGs. 2 and 3, which together comprise rectifying means associated with a three-phase transformer having an iron core (not shown) , a primary winding (11) and a secondary winding (18) . Instead of a three-phase transformer, three single-phase transformers may be used. For a three-phase supply, the primary 11 has three windings 12, 13 and 14 and they are illustrated in delta connection providing three input terminals designated 15, 16 and 17 in FIG. 3, to which lines 4, 5 and 6 are connected as shown.

The secondary 18 of the rectifier transformer comprises six windings 19, 20, 21, 22, 23 and 24 having a common central connection 25 forming one terminal 26 on the output side of the rectifying means 7. Terminal 26 may be grounded, as illustrated at 27, and it is sometimes referred to herein as the common, neutral or grounded terminal. Line 9, which FIG. 1 shows to be connected to terminal 26 of rectifying means 7a, is also sometimes referred to herein as the neutral, common or grounded line.

The rectifier transformer is constructed, wound and connected as described on page 573 and as illustrated in Fig. 486, page 574, of the textbook entitled, A Course in Electronical Engineering, Vol. II, Alternating Currents, Fourth Edition, by Chester L. Dawes, McGraw - Hill Book Co., 1947. The current delivered by the rectifying means 7a to lines 8, 9 and 10 and the voltages across

SUBSTITUTE SHEET these lines are relatively smooth. When the EMF of each winding is plotted against time, the envelope of the successive positive peaks has a maximum variation of 13.3%, i.e., taking the peak or maximum EMF across center connection 25 and the end terminals 28, 29, 30, 31, 32 and 33 of the six windings of the secondary as unity, the minumum EMF is 0.867, as illustrated in Fig. 487 (a), page 574, of Dawes for the envelope of the sine waves El, E2, E3, E4, E5, and E6. By the optional use of a smoothing inductance and/or capacitance in the load line, as hereafter mentioned for the circuits of the invention, the ripples in the load current become still smaller so that they may be neglected without serious error, as they also did in the very different load circuit of the Dawes mercury arc rectifier described on pages 533 to 576.

Each said end terminal 28 through 33 of each secondary winding 19 through 24 is connected to the mid-point of a bifurcated line having in one leg an outwardly oriented diode 34 and in the other leg an inwardly oriented diode 35. The cathode of each diode 34 is connected to a common line 36, and the anode of each diode 35 is connected through its leg of the bifurcated line to a different outer end of a secondary winding 19 through 24. Similarly the anodes of each of the six diodes 35 are connected to a common line 37 and the cathodes are each connected through its leg of the bifurcated end to a different outer end of a secondary winding 19 through 24. Common line 36 is connected to terminal 38 and common line 37 to terminal 39 on the output side of the rectifier 7. It is to terminal 38 that line 8 is connected and to terminal 39 that line 10 is connected, as shown in FIGs. 1 and 2. The voltage between terminals 26 and 38 is the same, except for polarity, as the voltage between terminals 26 and 39 and the voltage between terminals 39 and 38 is double that, as shown in

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SUBSTITUTE SHEET φ?NATiqS> FIG. 2. What these voltages are is a matter of design of the secondary windings with respect to the primary windings. In practice it is satisfactory if the peak voltage across a secondary winding is 170 volts, therefore, the DC voltage across terminals 26 and 38 and across terminals 26 and 39 will also be approximately 170 volts; the voltage across terminals 38 and 39 is double that or 340 volts.

The rectifier transformer may also be used to supply AC power to energize AC loads such as convenience outlets and AC motors. It is popular practice at present in the U.S.A. to distribute power to large buildings at 277/480 volts, three-phase AC and to energize the lighting systems directly from this source. The convenience outlets and other loads require 120 (110 to 130) volts and it is present practice to use numerous dry-type transformers throughout the building to convert 480 volt, three-phase current to 120/208 volts. Voltage standards may differ from U.S. standards in other countries, but in any event, the transformer used in the rectifier shown in FIG. 2 will supply current of desired phase and voltage, e.g., 120 volt single-phase current to a load, if the load is connected either to terminal 28, 30 or 32 and to neutral point 25, or three-phase current to a load if the load is connected to terminals 28, 30 and 32, or single-phase 208 volt current to a load if the load is connected to terminals 28 and 30, or 28 and 32, or 30 and 32. Furthermore, single-phase outputs of 120/240 volts can be obtained from terminals 28 and 31 and neutral point 25, in a three-wire system, as shown schematically in FIG. 5, or equally well from terminals 29 and 32, or 30 and 33 and neutral point 25. The output terminals for the circuits of FIGs. 4 and 5 will be located in the output side of the rectifier 7 (although they are not rectified and not shown in FIG. 1) and have

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SUBSTITUTE SHEET ^ ° been given the designations 28, 30 and 32, and 28, 25 and 31, respectively for convenience of reference. The rectifier of FIG. 2 incorporates a three-phase transformer such as is utilized in modern building power distribution systems to furnish power for 120, 208, or 240 volt AC loads. By making combined use of the same transformer in the DC power supply system of the invention, lower cost of the total system is achieved than in prior art high-frequency lighting systems.

If desired, DC output voltages other than plus and minus 170 volts can be obtained from the rectifier of FIG. 2. Thus, lower voltages may be obtained merely by connecting the twelve diodes 34 and 35 to taps (not shown) on secondary windings 19 to 24, inclusive, and higher voltages may be obtained by providing extensions (not shown) to the said windings. DC outputs of plus and minus 120 volts are especially desirable because of previously established standards of potential use in appliances other than the present lighting system.

The three-wire DC distribution system has the advantage over a two-wire DC system that smaller wires may be used, the secondary windings 19 through 24 are more fully utilized, with each conducting twice each cycle, no direct current flows in any of these windings nor in the neutral line 25 if the DC loads are equal on the positive and negative lines 36 and 37, and the positive DC power supply may continue to operate in the event of failure of the negative supply, and vice versa.

In the operation of the illustrated rectifier, each of the six secondary windings 19 through 24 produces a sinusoidal alternating voltage varying over a cycle from minus 170 to plus 170 volts. Because of the three-phase excitation of the primary 11 of the transformer, the voltages of the outer terminals 28 through

SUBSTITUTE SHEET 33 of the six secondary windings will reach their positive peaks at different successive times equally spaced within a cycle of the low-frequency current. At any instant, one of the terminals 28, 29, 30, 31, 32 or 33 will be more positive than all of the other terminals in this group and approximately 170 volts more positive than the neutral point 25. The diode 34 connected to the more positive terminal connects that terminal to conductor 36. The remaining five diodes are in non-conducting states at this instant. As time progresses, each of the other five diodes 34 conducts in turn, one at a time, to connect the most positive winding to conductor 36. Thus, conductor 36 remains at all times approximately 170 volts more positive than the neutral point 25 and the AC transformer voltages have been rectified to DC voltage. The six diodes 35 operate in a similar manner one by one to connect the most negative terminal from the group 28 through 33 to conductor 37 which remains approximately 170 volts more negative than neutral point 25. The rectifier of FIG. 2 produces a good, low-ripple DC output of about 4.5% ripple while preserving a high power factor of about 95.5% in the three-phase supply circuit 4, 5, 6.

The three-wire DC lines 8, 9 and 10 supplied from terminals 38, 26 and 39, respectively, of rectifying means 7a are connected to a plurality of loads across lines 8 and 9 for one load circuit and across lines 9 and 10 for another load circuit, and for greatest efficiency these loads may be balanced. Each load is an inverting means 40 connected to fluorescent lamps 67 in various numbers and arrangements. Six such inverting means are shown by way of example in FIG. 1. They are given letter designations a through f for ease of reference but in the following description of the inverting means illustrated in FIG. 6 the general designation 40 is used and the description of the circuit of FIG. 6 applies to each inverting means 40a through 40f. Inverting means 40a, 40σ and 40e are in parallel across lines 8 and 9 while 40b, 40d and 40f are in parallel across lines 9 and 10. While a total of six inverting means is given by way of example, the invention comprisesany desired number thereof in the output circuit of a single rectifying means 7 from one to as many as the rating of the rectifying means permits. Any person skilled in this art can readily determine the maximum number of inverting means of given rating which the rating of the rectifying means permits. Each of the rectifying means 7b, 7c and 7d also has a load circuit described and illustrated for rectifying means 7a

The fluorescent lamps 67 in FIG. 1 have been given postscripts identifying them with the particular inverting means 40a, 40b, 40c, 40d, 40e and 40f which supplies them with high-frequency alternating current. Thus, the lamps supplied from inverter 40a are designated, 67al and 67a2 which are in series, 67a3 and 67a4 which are in parallel, 67a5 and 67a6, each of which is supplied individually. Similarly, the lamps supplied from inverter 40b are designated 67bl and 67b2, each supplied individually, and 67b3 and 67b4 in parallel. Likewise -lamps supplied from inverter 40c are designated 67cl, 67σ2 and 67c3, all supplied individually; lamps supplied from inverter 40d are designated 67dl and 67d2, each supplied individually; lamps supplied from inverter 40e are designated 67el and 67e2 and are arranged in parallel; and the lamp supplied from inverter 40f is designated 67f.

Fluorescent lamps have to be electrically connected to the high frequency AC and to be held in place during use. In general, it is customary in the art to use fixtures as the receiving or holding means with one or more pairs of properly spaced sockets secured in said fixtures as the means for electrically connecting

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SUBSTITUTE SHEET ^ fry, Z WIFτO $ j the lamps to the high frequency AC from the inverter. The standard sockets for filament-type lamps permit removal and replacement of a lamp. Each socket has one or two contacts to electrically engage the contact pins or terminals at the ends of the fluorescent tube. In filament type lamps, each end has two contact pins to which the filament is connected and when the lamp is properly installed in the socket at each end the filament is connected to the source of heating current.

THE INVERTING MEANS

Referring now to FIG. 6, the inverting means 40 comprises a positive input terminal 41 and a negative input terminal 42. These terminals, 41 and 42, are adapted to be connected to the direct current lines from the rectifying means 7, e.g., across lines 8 and 9 or across lines 9 and 10. In the event a source of direct current other than the rectifying means 7 is used, which the invention comtemplates as mentioned above, terminals 41 and 42 would be connected to whatever source is to be used, e.g., a battery circuit for emergency use or use remote from a commercial source of power, a solar cell, a fuel cell, or the like. On the output side of the inverting means 40 are two output terminals 43 and 43a for the high-frequency current generated in the inverting means 40 by the means now to be described in detail. The entire circuit from input terminals 41 and 42 to the output terminals 43 and 43a comprises each inverting means 40a, 40b, 40c, 40d, 40e and 40f.

The inverter means 40 further comprises two transistors 44 and 45 which are the active elements of a high-power, push-pull, c ass-B, tuned-collector, current-driven oscillator. An oscillator of the sort, intended to produce a large amount of AC power from a DC source, is commonly denominated in this art as an inverter and that name is generally used herein for the containing of such elements of the circuit of the invention as herein described. Transistor 44 has a base 46, a collector 47 and an emitter 48. Transistor 45 has a base 49, a collector 50 and an emitter 51. The tuned circuit comprises inductors or windings 52 and 53 of an inverter transformer 54 which has a magnetic core 55, e.g., a ferrite core. Windings 52 and 53 have a common center 57 and end terminals 58 and 59 which in turn are connected to collectors 47 and 50 by lines 65 and 70, respectively. This circuit is tuned to oscillate or resonate at a frequency of at least 20 kHz in order (1) to enhance the efficiency of fluorescent lamps, (2) to be inaudible and (3) to make possible the utilization of small and practically loss-free circuit components. Collector inductors 52 and 53 are wound on the magnetic core 55 of transformer 54, along with other windings which are described hereafter. In operation, a high AC voltage of sinusoidal waveform appears across the end terminals 58 and 59 of inductors 52 and 53. A feedback winding 61 is provided on a core 55 and by transformer action a much smaller voltage is induced in it than in windings 52 and 53 because of the small number of turns it has. The end terminals of feedback winding 61 are connected respectively to bases 46 and 49 of the transistors 44 and 45. The polarity of the feed-back voltage is selected to provide positive feedback from collectors to bases as required to maintain or sustain oscillation. The transistors operate in an efficient alternate switching mode, one being turned off completely at one instant while the other is saturated at which time it is turned fully on and is equivalent to a closed switch. The feedback signal to the bases causes switching from one state to the other. The transistor with the more positive base voltage is saturated or in the "on" state. The transistor with the more negative base voltage is in the "off" state. A brief transitional interval is required to complete switching from one state to the other.

SUBSTITUTE SHEET Direct current flowing into the inverting means 40 from the rectifying means 7, or other power source as described above, enters at the positive terminal 41 which is connected by conductor 62 to the center terminal 57 of windings 52 and 53 through a fuse 63, a diode 64 and an inductor or winding 76 on a magnetic core 66. inductor 76, as described more fully hereinafter, serves to maintain a constant current in line 62. Instead of being in line 62, it may be in line 69, if desired. At the central terminal junction point 57 the current must take one of two alternate paths. One path comprises inductor or winding 52, terminal 58, line 65, collector 47, emitter 48 of transistor 44, line 68 and line 69 which return current to the rectifying means 7 or other source through terminal 42. The current takes this path when transistor 44 is in conducting mode. The other path which the current takes, when transistor 44 turns off and transistor 45 turns on, comprises winding 53, terminal 59, line 70, collector 50, emitter 51 of transistor 45, line 69 and terminal 42, thus returning the current to the rectifying means 7 or other source along this second path. Current flowing alternately through windings 52 and 53 of transformer 54 produces an alternating voltage in every winding on the core 55, which is the desired result of the action of inverting means 40.

Transistors can generally turn on more quickly than they can turn off. Consequently, one transistor will turn on before the other transistor has turned completely off. This results in an actual short circuit across the terminals 58 and 59 of the windings 52 and 53 for a brief interval at each switching time. This short circuit is rendered harmless because inductor 76 maintains an essentially constant current through itself and associated parts of the circuit and thus prevents the transistor collector currents from rising appreciably during the short circuit or conduction overlap period. The transistors thus start and complete their switching actions under ideal conditions of practically zero collector voltage and externally limited collector current.

Resistor 71 in line 72, which connects conductor 62, e.g., at the junction of adjacent terminals of diode 64 and inductor 76, with the mid-point of feedback winding 61, conducts a small current from the positive DC input terminal 41 and conductor 62 to the gates 46 and 49, respectively, of the two transistors 44 and 45 by way of feedback winding 61. This is the only source of base current when the inverter is first turned on and is essential for reliable starting. As oscillations build up, most of the base current comes from voltage induced^' in the feedback winding 61, as will be described in more detail hereafter.

Diode 64 is optional and, when used, prevents the blowing of fuse 63 if the input terminals 41, 42 are connected to the DC supply lines 8, 9 or 9, 10 of wrong polarity.

Diode 73 connects the base 46 of transistor 44, and diode 74 connects the base 49 of transistor 45, to line 69 through resistor 75 and winding 80 on core 66, where used as described hereinafter. The difference in the operation of the circuit of the invention over the typical prior art base connection arrangement may be clearly understood by comparing FIG. 7 with FIG. 6. In FIG. 7, comparable parts have the same reference numbers used in FIG. 6 with a postscript a.

The typical prior art base connection arrangement comprises two transistors 44a and 45a, a single diode 73a connected in series with inductor 80a and resistor 75a, and this combination connects the center tap of feedback winding 61a to the emitters 48a and 51a of both transistors 44a and 45a. The purpose of this circuit is efficiently to provide a large DC component of base current by rectifying the low voltage of the feedback winding 61a. The base-emitter junctions of the transistors provide the

TUTE SHEET rectifying action, and the inductor 80a maintains base current in at least one transistor during the switching instants when the alternating feedback voltage passes through zero. Diode 73a merely prevents the draining away of the small starting component of base current from resistor 71a. Neither base can rise more than about 0.8 volt above the emitters because of the transistor characteristics. This requires that most of the feedback voltage across winding 61a will show up as negative voltage at the base of the "off" transistor, whichever that may be at any given time. Also, the center tap of winding 61a will be driven negative twice each cycle at the one time each cycle when each base goes negative. As the center tap goes negative, current flows upward through diode 73a, inductor 80a and resistor 75a and continues into the base of whichever transistor is turned on. This current is largely responsible for turning the transistors on. As stated previously, the inductor 80a keeps the current through itself substantially constant, providing a steady source of current for one or the other of the bases.

With this prior art circuit, the maximum voltage across the feedback winding 61a is necessarily only a few volts, as limited by the peak reverse voltage rating of the emitter-base junctions of the transistors. A significant portion of this voltage is lost in diode 73a and in the emitter-base junctions of the transistors. Thus, when feedback voltage is reduced because of low-line voltage, as may be experienced during a "brown out" and at other times, the base drive voltage becomes unreliably small, and a condition of intermittent oscillation can occur. In particular, the transistors may not saturate but conduct current while a large voltage exists from collector to emitter, increasing power dissipation which may quickly damage the transistors.

tfRl OMPI

SUBSTITUTE SHEET With the present invention, as shown in FIG. 6, two diodes 73 and 74 are connected one at each end of the feedback winding 61, rather than having a single diode at the center tap as shown in the prior art circuit in FIG. 7. This doubles the voltage available for rectification and allows stable operation down to such low input voltages that the transistors are adequately protected for all low voltage conditions.

Inductor 80 is not always required in FIGs. 6 and 7. However, when used, it can reduce peak base current and reduce the power dissipated in resistor 75a (FIG. 7) or resistor 75 (FIG. 6). A more economical way to implement the equivalent inductor 80a in FIG. 7, if such is desired, is to substitute for inductor 80a a few turns of wire 80 around the core 66 of inductor 76, as shown in FIG. 6, connected in series with resistor 75. Transformer action from the main inductor winding 76 then induces the same voltage in these few turns 80 that inductor 80a would ideally have, but without the expense of an additional magnetic core and bobbin. Winding 80 adds an AC voltage at the bottom of resistor 75 equal to the AC component of voltage from feedback winding 61 at the top of resistor 75, leaving only a DC voltage across resistor 75, resulting in the same constant base current provided in prior art by the additional inductor 80a.

A small capacitor 83 is preferably connected between the junction 57 of collector windings 52 and 53 and the feedback winding 61. This capacitor helps speed the switching action by drawing base current away from the base of whichever transistor is turning off at the proper time and by adding base current to the turning-on transistor a moment later.

Diode 84 and Zener diode 85, when used, are arranged in series with each other and across inductor 76, as shown, to limit the maximum positive voltage that can be applied to the transistor circuit. A dangerous voltage capable of destroying the transistors

SUBSTITUTE SHEET S X o can otherwise occur during the transient condition when the inverter is first switched on to the low-impedance voltage source from the central rectifier 7.

A diode 86 may be placed across the DC input lines. This diode conducts only for an instant when the DC input power is switched off. It provides a controlled path for decay of the current stored in inductor 76 when that current can no longer flow through the input line 62. Diode 86 also reduces arcing at the switch (not shown) which turns off the DC input voltage. Diodes 84 and 86, Zener diode 85 and capacitor 83 comprise transient suppression circuitry.

In the preferred embodiment shown the several windings are placed on transformer core 55. This avoids the use of two more costly individual transformers, as are commonly used in the prior art.

The AC output of the inverter can be used in many ways. FIG. 6 illustrates how three, or more, "rapid start" fluorescent lamps 67a5, 67a6 and 67a7 can be driven. These lamps have electrodes in the form of filaments at each end thereof, which must be heated by a flow of current produced by means of a low voltage. For ease of description, the filaments in lamp 67a5 are designated 90a5 and 91a5, those in lamp 67a6 are designated 90a6 and 91a6, and those in lamp 67a7 are designated 90a7 and 91a7, respectively. The heater voltage for the filaments 90a5, 90a6 and 90a7 is obtained from low voltage heater winding 92 on magnetic core 55. Filaments 91a5, 91a6 and 91a7 at the opposite end of each lamp require separate heater windings 93, 94 and 95 on the same core, as shown. Fluorescent and other gas discharge lamps have a negative impedance characteristic which makes direct parallel operation impractical. Each lamp requires a ballast impedance in series with it to limit the current. Either inductors or capacitors can perform the ballast function without wasting energy. Capacitors

OMPI

&>1 96, 97 and 98 are shown as ballasts in FIG. 6. Windings 52 and 53 constitute a sinusoidal high voltage, high-frequency power supply for the lamps. The voltage of these windings is determined almost completely by the DC voltage to the inverter, but the voltage applied to the lamps can be selected independently by tapping one or both of the windings 52 and 53 as shown at tap 99 for lower voltage. A higher voltage can be obtained by extending either or both windings with additional turns (not shown but cf. FIG. 8) beyond the points where the transistor collectors connect.

An entirely secondary separate winding (not shown but cf. FIGs. 11 - 14) on core 55, of any desired voltage, can be used for the lamps, and with full transformer isolation, if necessary or desirable.

Other loading arrangements are possible and more (or fewer) than three lamps can be accommodated by the system of FIG. 6 as shown in FIG. 1 and described above and in FIGs. 11 - 14 as described below. This parallel system of operation permits removal of part of the lamps from the fixture to reduce light intensity without appreciable effect on the remaining lamps. Lamps can also be operated in series or series-parallel, particularly if there are an even number of lamps. Such an arrangement reduces the number of ballast capacitors needed and makes dimming by adjusting ballast capacitance entirely feasible, as more fully described hereinafter.

Many fluorescent and other gas discharge lamps do not require separately heated filaments, and if such lamps are used, the heater windings 92, 93, 94 and 95 would not be needed.

FIG. 8 shows that portion of the circuit of FIG. 6 that may be modified for series operation of two rapid start lamps 101 and 102. Parts in the circuit of FIG. 8 that correspond to parts in the circuit of FIG. 6, are given the same reference number with the postscript b and need not be further discussed at this point.

-^JRIX;

OMPI ITUTE SHEET Voltage greater than that between the transistor collectors is obtained by adding one or two extension windings 103 and 104 to the core 55b. Windings 92b, 106 and 110 then provide heating power for the lamp filaments, 105, 107, 108 and 109. A single capacitor 111 provides current limiting or ballasting for both lamps.

DIMMING

Rapid start fluorescent lamps are readily dimmed by lowering the capacitance of the ballast capacitor 111 in FIG. 8. One simple means is to make capacitor 111 from a number of separate capacitors which can be switched manually or remotely into the circuit in various combinations by conventional switch means (not shown) . Another means adaptable to adjustable zone lighting is to plug in different values of capacitor 111 in accordance with a desired lighting level. Dimming by adjustment of the ballast capacitor allows for full starting voltage at all light levels and is superior therefore to voltage reduction methods. The preferred dimming method described keeps filament voltages constant, as is usually desired when dimming.

Dimming is also readily achieved by the circuit illustrated in FIG. 14 as fully described hereinafter.

FLASHING

The inverter 40 is readily adapted to utilize electronic control for flashing. This requires only a modification of a portion of the circuit of FIG. 6. Such a modified portion of the circuit is shown in FIG. 9 in which parts comparable to parts in FIG. 6 have been given the same reference numbers with a postscript c and need no further description here. A separate transformer 112 having a magnetic core 113, a primary winding 114 with terminals 115 and 116 adapted to connect the primary to an AC source of any frequency, and a series of secondary coils 92σ, 93c, 94c and 95c for heating the filaments of lamps 67a5c, 67a6c and 67a7c, operating independently of the inverter keeps the filaments

OMPI always heated, so that filament windings from the inverter itself are not needed. DC power into the inverter is controlled by transistor 114 which can be turned on and off by a low-level signal (less than 1 volt) between the base 115 and ground 116. This method of switching is superior to and easier to accomplish than switching in an AC circuit. A mechanical switch could replace transistor 114, if desired.

FILAMENT CONTROL FIG. 10 shows a modified form of the circuit of FIG. 8 in which comparable parts have been given the same reference numbers with a postscript d. The filaments of lamps løld and 102d are supplied from a transformer 54d instead of directly from the constant-voltage inverter transformer 54 of FIGs. 6 and 8. The primary 52d of transformer 54d receives its voltage input from the voltage across the lamps. Before the arc strikes in the lamps, there is little voltage drop in the ballast capacitor llld and practically the full inverter voltage is applied to the primary of the transformer 54d. This results in a relatively high output in secondary windings 92d, 106d and llød of transformer 54d to heat the filaments rapidly. As soon as the arc strikes, the lamp arc voltage drops substantially, lowering the voltage on all windings of transformer 54d and specifically reducing the heater voltages on windings 92d, 106d and llød. Reduced heater voltage means that less power is consumed and the circuit operates more efficiently than it would otherwise do. No switches are needed to accomplish heater power reduction, in contrast to the practice in some prior art systems. Placing the heater windings on transformer 54d simplifies the design of already complicated transformer 54. Because of the high frequency used, transformer 54d can be very small, inexpensive, and free from power loss. Note that the heaters are not shut off entirely since this would be harmful to the life of some filaments. The greatest damage to filaments

SUBSTITUTE SHEET normally occurs during starting when they are bombarded by heavy ions before they reach proper operating temperature. The control offered by transformer 54d shortens this time of bombardment and assures increased lamp life as well as improved operating energy efficiency.

FIG. HA depicts a circuit which is capable of supplying a high current to the filaments of a heated filament fluorescent lamp when the lamp is first turned on at the start of a lighting cycle and automatically reducing the current flow through the filaments as soon as stable operation is achieved. This circuit comprises an inverter illustrated by the block 120 (which may have the same circuit described above or it may have any other circuit which will accomplish the same function) , a ballast represented by the block 122 (which may be any electronic component serving this function such as an inductor or capacitor) , an electric connection 124 between the inverter and the ballast, a line 125 from the ballast 122 to a load 126 to be described more fully hereuπder, and a return connection 128 to the inverter 120. The load illustrated comprises an autotransformer 130 having one terminal connected to line 125 and the other terminal connected to line 128, a fluorescent lamp 132 having a filament 134 at one end and a filament 136 at the other end. The current for filament 134 is supplied from one end of the autotransformer 130 by a tap 138 just a turn or a few turns from that end while the current for filament 136 is supplied from the other end of the autotransformer by a tap 140 just a turn or a few turns from said other end.

After the inverter 120 has been turned on and before the arc has been struck between the cathodes or filaments 134 and 136 of the lamp or tube 132, very little electric current flows through the lamp and ballast circuit. Accordingly there is little voltage drop in the ballast impedance 122, and essentially all the voltage from the inverter 120 appears across the entire winding of the

OMPI

SUBSTITUTE SHEET autotransformer 130. Voltages suitable for quickly heating the filaments or cathodes 134 and 136 are induced in the end turns of the autotransformer beyond taps 138 and 140, respectively. After a short period of heating, sufficient electrons are emitted by the cathodes or filaments 134 and 136 to permit an arc to be established between the cathodes. A large electric current then flows through the lamp and ballast, and a large voltage drop occurs in the ballast. The voltage remaining across the lamp terminals (between the filaments or cathodes) drops to a much lower value, e.g. about half its former value, more or less. This lamp voltage is applied to the autotransformer, so the voltage in every part of the autotransformer winding drops to the lower value. In particular, the voltage in the heater turns beyond taps 138 and 140 drops and reduces the cathode heating voltage to the said lower value. The direct heating power for the cathodes depends on the square of the voltage, so the heating power drops to substantially less than half its former value. Typically 2/3 of the energy used for direct cathode heating can be saved by this means. Note that no switches, electronic or otherwise, are needed and that the lamp-ballast filament transformer circuits are connected to the inverter by only two conductors. Thus the circuit is inexpensive and convenient for use in a lamp fixture separate from the one containing the inverter. As such, a system including several one-lamp or two-lamp fixtures can be operated from a common inverter which for economy should be loaded to its full capacity.

Not only does the autotransformer 130 allow energy saving, but it does so without the disadvantage of certain prior-art ballasts which turn the heaters off completely. A definite voltage maintained across the length of each cathode encourages the intercathode arc to form first between the ends of the cathodes where the voltage difference is greatest. A hot spot forms there

BSTITUTE SHEET where most of the electron emission takes place. As the electron-emitting oxide is burned away from one end of each cathode, the hot spot moves to an adjacent spot having the next highest voltage and in this manner progresses in an orderly way along the entire filament throughout the useful life of the lamp. If a definite voltage is not provided across the filament, the hot spot may wander out of control and may never reach some portions of the cathode still having good oxide coatings. Premature cathode failure results.

In summary, one feature of the present invention provides means to maintain sufficient voltage across each cathode to promote orderly hot spot migration while saving 2/3 of the cathode heater power.

One filament transformer similar to 130 but with additional filament windings, some of which are not conduσtively connected together as in an autotransformer but isolated as in a conventional transformer, can serve two more lamps connected in series in a straight-forward extension of the circuit described above.

In applications not needing to conserve heater power, the heaters can be energized in this system, as in prior-art, directly from additional windings (not shown) on the main inverter transformer or from one or more intermediate transformers with primary windings connected to the inverter output ahead of the ballast impedances,

FIG. IIB illustrates a modification of the circuit of FIG. HA which provides constant heater power. In this figure, parts which are the same as comparable parts in FIG. HA have been given the same reference numbers with a subscript a and need not be described again for the circuit of FIG. IIB, The significant difference in the circuit of FIG. IIB over the circuit of FIG. HA is that the filament transformer 130a is connected across lines 124a and 128a between the terminals 142 and 144 to be connected to an inverter (not shown), e.g., such as 120, and the ballast 122a. Filament 134a is supplied with current from a short secondary winding 146. Filament 136a is supplied with current from a tap on winding 130a a turn or a few turns from an end thereof. The voltage across the transformer is not affected by voltage drop in the ballast impedence 122a and does not change substantially with current flow so that the voltages supplying current to the filaments 134a and 136a remains practically constant during operation of the lamps. The high-frequency transformer 130a is preferably a transformer having a magnetic core, e.g. ferrite core, 148.

FIG. 11C depicts a further circuit modified from that of FIG. HA which also has such comparable parts numbered with the corresponding part number in FIG. HA but with a subscript b. The difference is that the autotransformer 130b has taps 138b and 140b one or a few turns from the ends of the winding connected to lines 125b and 128b and the leads to the filaments 134b and 136b connect to the end terminals of the transformer rather than the taps on the winding. The operation of the circuits of FIGs. HB and HC is essentially the same as described for the circuit of FIG. HA. supply full voltage of lines 124c and 128c across both lamps 152 and 154 at the start of lamp operation (as do the circuits of FIGs. HA and HC) , but to reduce the voltage substantially during operation by the voltage drops across ballast capacitor 164 and ballast inductor 182.

The second circuit 184 comprises a single fluorescent lamp 186 having a filament 188 at one end and a filament 190 at the other end. It receives constant filament power from an intermediate autotransformer 192 connected across lines 124c and 128c by lines 194 and 196, respectively. Filament 188 is supplied with heating current by a transformer 198 having a high frequency

STITUTE SHEET core 200, e.g., ferrite. One end of the autotransformer winding 192 forms the primary of transformer 198. The secondary is a winding 202 connected at one end to one end of the filament 188 and at the other end to a line 204 which is connected at one end to the other end of the filament 188 and at the other end to the junction of said connection of winding 202 to line 204 and one terminal of ballast capacitor 206. The other terminal of capacitor 206 is connected by line 208 to line 124c. Filament 190 has one end connected by line 210 to line 196 and the other end connected by line 212 to a tap 214 on autotransformer winding 192.

The third circuit 216 bears the same reference numbers to parts corresponding to circuit 184 with postscript a and is the same as the second circuit 184, except that the separate transformer 198 is eliminated by using a few turns of the autotransformer circuit at both ends, e.g., by connecting the one end of filament 188a to a tap 202a on the winding 192a a few turns from the end. The filaments of lamp 186a receive variable power from this circuit, i.e., the filament voltage is reduced after the lamp arc strikes.

The fourth circuit 218 is the same as circuit 216 except that the ballast capacitor 206a is replaced by a ballast inductance 206b. Other parts bear the same reference numbers as the corresponding parts in circuits 184 and 216 with a postscript b and need not be further described. The combination of capacitor 206a for ballast in circuit 216 with inductor 206b for ballast in circuit 218 gives high power factor.

The circuits 184, 216 and 218, as is true of all of the circuits, operate in essentially the same way, providing full voltage of the inverter to which lines 124c and 128σ are connected across the lamp at the start and a much reduced voltage after it is operating steadily. In circuit 184, full voltage is applied to the filaments at all times, whereas in circuits 216 and 218, the

SUBSTITUTE SHEET f OMPI voltage applied to the filaments is automatically reduced when the voltage across the lamps decreases.

The fifth circuit 220 comprises two fluorescent lamps 222 and 224 in series across lines 124σ and 128c and are served by a single filament transformer 192c. Lamp 222 has one filament 226 connected at one end to a tap 202c on autotransformer winding 192c, as in circuit 216, and at the other end to the end of transformer winding 192c, and through capacitor 206c and line 208c to line 124c. Filaments 190c at one end of tube 228c is connected at one end to tap 214σ on transformer winding 192c a few turns from the end, and at the other end by lines 210c and 196c to line 128c. The adjacent end filaments 227 and 228 of lamps 222 and 224, respectively, are connected in parallel across the terminals of a short winding 230 forming a secondary of a transformer of which the primary is winding 192c. Optionally, a small capacitor 232 (or inductor) connected across lamp 224 (or across lamp 222 instead) may be used to aid starting and reduce the need for high voltage for good operation.

The sixth circuit 234 is the same as circuit 220 except that capacitors 206c and 232 are replaced by inductances 206d and 232d, respectively. Other parts of circuit 234 have the same reference number as the corresponding parts of circuit 220 with the postscript d and need not be further described.

Circuits 220 and 234 operate in essentially the same manner as circuits 216 and 218 except that there are two lamps in series in circuits 220 and 234 instead of a single lamp in circuits 216 and 218.

FIG. 12 shows the great versatility of the circuits of the invention to modification without changing the principles of operation to operate with constant filament voltage or to achieve voltage reduction, across the filaments of lamps, with consequent reduction of heating current during operation after a maximum

SUBSTITUTE SHEET voltage start up, and with high power factor.

The invention includes a modified means illustrated in FIG. 13 which is slightly different from the means shown in FIG, 6 in that the current through resistor 71d of relatively high resistance, e.g., 100 kilohms, flows (a) directly to base 46d and (b) through winding 61d and a resistor 240d of relatively low resistance e.g., 10 ohms, to base 49d, and feedback windings 79d and 79ad on core 55d are inserted in each terminal line from resistor 75d to diode 73d and to diode 74d, respectively. Base 46d is thus connected to base 49d through diode 73d, the two windings 79d and 79ad in series, and diode 74d, and to line 69d through diode 73d, winding 79d, resistor 75d, and choke coil 78d to supply the bases of transistors 44d and 45d.

Current flowing through this resistor 71d provides a very small initial bias current to assure reliable starting. The operation of the modified curcuit, referring to FIG. 13 is as follows: at least one of the transistors turns on and allows current to flow from terminal 41d through inductor 76d, center tap 57d and alternately through the primary windings 52d and 53d of the main inverter transformer 54d. A voltage is thus applied to coil 52d, 53d, and this induces a voltage in the low-voltage feedback winding 61d on the same core 55d. One terminal of winding 61d is connected to base 46d of transistor 44d. The other terminal of winding 61d is connected to base 49d of transistor 45d, through the aforesaid resistor 240d. Polarity of the feedback winding 61d is such as to reinforce whatever the transistors are doing. That is, if 44d initially conducts more heavily than 45d, the feedback signal will tend to turn 44d on still more, and 45d will be turned off. Capacitor 60d resonates with 52d, 53d and causes the voltage polarity to reverse periodically in all of the windings on 55d. First one transistor conducts and then the other. Winding 76d maintains a constant current through itself; therefore, the sum of

SUBSTITUTE SHEET ^ ≥ the two transistor collector currents must be constant. In the transition interval when switching from one transistor to the other, and when both transistors are partly turned on and windings 52d and 53d are shorted, 76d assures that excessive current will not flow.

Voltage is induced also in the higher voltage feedback windings 79d and 79ad connected through slow diodes 73d and 74d to bases 46d and 49d and .at mid-point to resistor 75d, and when oscillations build up enough that this voltage can turn on diodes 73d and 74d, most of the transistor base current is supplied from this new source. It is far more efficient to obtain base current from the few turns of these two windings on core 55d than from the 120 volt input source. Only about 1.2 mA of base current flows through resistor 71d while about 80 mA comes from these two windings 79d and 79ad. This arrangement saves about 9 watts. Diodes 73d and 74d also have other important functions. They, of course, force the starting current from 71d to flow into the transistor bases instead of being drained away through resistor 75d. Diodes 73d and 74d also connect both relatively high voltage feedback windings 79d and 79ad to both bases at the switching time to provide a large feedback signal to assure fast switching and very rapid turn off for one transistor and rapid turn on for the other. Diodes 73d and 74d are slow diodes having a longer charge storage time than the transistors 44d and 45d. Thus, while one diode conducts normally, the other will conduct backward for a short time until the transistor to which it is connected is fully turned off. However, before the base is driven too far negative, that diode will cease to conduct, and the base can drop only as far as allowed by the low-voltage feedback winding 61d, (e.g., to about -4.5 volts) .

SUBSTITUTE SHEET The voltage at the common junction of the two feedback windings 79d and 79ad with resistor 75d has a negative DC component of about 4.5 volts with respect to terminal 42d and an AC component consisting of a train of half-sine waves. It turns out that the AC component at this common junction has the same wave form as that at the center tap 57d, except for polarity and amplitude. The AC component at the center tap 57d appears across winding 76d. By adding a second winding 78d, of very few turns on the same core 66d, and connecting it as shown, the AC component of voltage between resistor 75d and winding 78d can be made almost exactly the same as that at the junction of 75d with the two feedback windings 79d and 79ad. The potential across resistor 75d is therefore almost a pure 4.5 V DC voltage, and a constant current of about 80 mA flows up through resistor 75d and into one base or the other of transistors 44d and 45d. Since the sum of the collector currents is held constant by inductance 76d, it is proper and efficient to have the sum of the base currents constant also.

If the voltage at the center tap 57 of FIG. 6 or 57d of FIG. 13 ever rises sufficiently far above terminal 41 or 41d, Zener diode 85 or 85d turns on and prevents further rise to protect the transistors. Abnormally high voltage can occur at center tap 57 and 57d for a few cycles at turn on. Diode 84 is used to prevent 85 from conducting when the voltage at center tap 57 drops below that at terminal 41, as happens in normal operation.

Diode 86 and diode 86d function only at turn off to allow a discharge path for current in windings 76 and 76d, respectively.

Capacitor 81d helps to reduce radio noises conducted back, into the DC supply line. Inductances 76 and 76d are also very effective in this regard, although that is not the main function thereof.

OMPI ? A secondary winding 237d may be wound on core 55d of transformer 54d to provide output terminals 43d and 43ad at the ends thereof in place of, or if desired, in addition to the output terminals 43 and 43a of FIG. 6.

Lamps may be connected to either pair of terminals in this modified circuit of FIG. 13 in essentially the same manner shown for lamps 67 in FIG. 6, using either ballast capacitors or inductances or both.

Each lamp or pair of lamps operates independently from the others and each has its own ballast inductor or capacitor. By using both inductors and capacitors, t±e reactive effects cancel so far as the inverter is concerned. The load power factor is therefore high, and the inverter frequency is relatively independent of the load in case some of the lamps are removed.

Air gaps are used with both inductors or transformers 54 and 76 and also with the ballast inductors. A DC input voltage of about 120 V was selected because of the commercial availability in the U.S.A. of switches and circuit breakers of this rating, and this also permits incandescent lamps to be run from the same circuit. Other voltages may be used where switches and breakers of other ratings are commercially available.

Lamp filaments can be powered in the modified circuit of FIG. 13 from 1-turn windings on t±e core of transformer 54d, t±e same as in FIG. 6. One winding can serve one end of all the lamps which may be connected together, but individual windings are needed at the ballast ends. Alternatively, one or more separate filament transformers can be used to reduce the number of wires to lamps not contained in the same fixture with t±e inverter or to reduce filament power after lamps turn on.

O PI Ar^ WIPO - The circuit of FIG. 6 and the modified circuit of FIG. 13 may be modified by the addition of a diode in lines 65 and 65d, respectively, and a diode in lines 70 and 70d, respectively, which serve to assure the absence of any reverse flow of current in lines 65 , 65d and 70, 70d.

The connecting of the anode of t±e Zener diode 85, 85d into the circuit, which in FIG. 6 is connected (through diode 84) across inductor 76 is,, in the modified circuit of FIG. 13, connected directly to base 46d of transistor 44d and through winding 61d and t±e resistor of lower resistance 240d to the base 49d of transistor 45d. The anode of t±e Zener diode may, instead, be connected directly to line 69, 69d. The connection of line 62 to line 72 through Zener diode 85b and 84d causes the input DC voltage (120 V) to be added to the conduction voltage of Zener diode 85 which should be designed to conduct at about 120 V for the required 240 volts maximum at mid-point 57. In the modified circuit of FIG. 13 and the aforementioned modification thereof which eliminates diode 84 and connects the anode of Zener diode 85d directly to base 46d or line 69d, Zener diode 85d must conduct at about 240 volts. Diode 84, when used, prevents Zener diode 85 from conducting when the cathode of Zener diode 85 drops below 120 volts as it periodically does in normal operation. The direct connection of t±e anode of Zener diode 85 to the negative input terminal 42 when it is connected directly to line 69 is the most straghtforward alternative, but requires a higher combination of voltage and current in Zener diode 85 than do the alternative connections described-.

The modified circuit of FIG. 13 in which the anode of Zener diode 85d connects directly to base 46d may be furt±er modified by the addition of two further diodes 299 and 300. Diode 299 has its cathode connected to collector 47d of transistor 44d and its anode connected to the junction of t±e anode of diode 73d and feedback

TITUTE SHEET winding 79d and the other having its cathode connected to collector 50d of transistor 45d and its anode connected to t±e junction of the anode of diode 74d and feedback winding 79ad. With these two diodes in the circuit, the resistance rating of resistor

75d can be selected to provide that all the base current not needed by transistors of normal or high gain be shunted by these two diodes 299 and 300 (hence catching diodes) away from the base to the collector of either transistor as that transistor approaches saturation. The result is that t±e transistors do not quite saturate and can be turned off more quickly than if allowed to saturate heavily. These two diodes 299 and 300, therefore, may further serve to adjust the inverter to accomodate transistors differing greatly in current gain. While these two further diodes have thus far been described only in the circuit having the anode of the Zener diode 85 connected directly to base 46d, they may also be used in the other circuits described if the benefits just described are desired in any one or more of these circuits.

Connection of the anode of Zener diode 85d to the base of either transistor 44d or 45d causes at least one of these transitors to turn on heavily when diode 85d turns on. Current flowing through the collectors of the transistors 44d and 45d can limit their collector voltages as effectively as current through Zener diode 85d but with the advantage that the transistors 44d and 45d are capable of conducting much larger currents than the Zener diode 85d needs to conduct in this situation. Thus by using the Zener diode 85d to turn on the transistors 44d and 45d, a relatively low-current and inexpensive Zener diode may be used.

The drive circuits for the transistors 44 and 45 just described represent a significant improvement over circuits known in the prior art. Two independent feedback windings of the main inverter transformer 54 are used to satisfy conflicting requirements in an optimum way. It is desirable to have a large

^SUB^STITU feedback voltage during t±e switching time to turn one transistor off and the other on with a minimum of overlap time when both transistors are partially on. However, a sufficiently large feedback voltage for this purpose causes too much reverse base voltage for the turned-off transistor between switching events if only one feedback winding is used, as in FIGs. 6 and 7.

A small current from the +DC source 41d flows through resistor 71d to supply a very small amount of bias current for the bases of the transistors 44d and 45d. This is sufficient to cause the transistors to begin to oscillate in the conventional way, i.e., the outputs of the collectors of both transistors are connected to transformer 54d by windings 52d and 53d which in turn are coupled magnetically to the transistor bases 46d and 49d by way of the low-voltage feedback winding 61d on the core of the same transformer. Feedback polarity is such as to reinforce and sustain an oscillating condition, with each transistor in turn causing current to flow from the positive DC voltage source 41 through inductor 76d, line 62d and then through either winding 52d or 53d of transformer 54d, and returning to the negative power supply terminal 42d.

When the amplitude of oscillation increases sufficiently, diodes 73d and 74d are turned on and off alternately by voltage induced in high-voltage feedback windings 79d and 79ad in t±e modified circuit of FIG. 13, as described. Base current is increased very substantially by current from either of these feedback windings and the bases are driven efficiently at this time primarily from this source. Although t±e voltage of these feedback windings is high compared to t±e voltage of winding 61d, it is still small compared to the input voltage at terminals 41d and 42d, which means that base current is obtained more efficiently from these feedback windings than from the high-resistance dropping resistor 71d.

%

OMPI Diodes 73d and 74d are inexpensive, low-voltage, slow diodes which have a larger charge storage time than the transistor bases 46 and 49. This means that when the anode of either diode 73 or 74 goes negative with respect to the cathode, that diode will not immediately turn off but will conduct backward and withdraw all of the stored charge in the base of the transistor connected thereto. The other diode has already turned on even sooner. Thus, during this critical switching time, the high voltage feedback windings are connected directly to both bases through very low-impedance diodes 73d and 74d, and the low-voltage winding is effectively isolated by resistor 240d. Before the voltage of t±e base of the turning-off transistor drops below a safe value, t±e associated diode runs out of stored charge (while also driving current through said series resistor) and turns off. The peak negative base voltage is therefore determined only by the low-voltage winding 61d, as desired. Current flowing through the collectors 47 and 50 of the transistors 44 and 45, respectively, can limit their collector voltages as effectively as current through Zener diode 85 but with the advantage that the transistors are capable of conducting much larger currents than the Zener diode 85 needs to conduct in this circuit. Thus, by using the Zener diode 85 to turn the transistors on, a relatively low current and inexpensive Zener diode may be used.

FIG. 14 depicts a circuit connecting essential parts of an inverter to two pairs of series connected fluorescent lamps with means for heating the filaments of all lamps and using both capacitor and inductor ballast for high power factor. Terminal 241 connects the inverter to the positive terminal and terminal 242 connects it to the negative terminal of a power supply line (not shown) . Current flowing into the inverter from terminal 241 flows through winding 243, which is analogous to winding 76 in the circuit of FIG. 6, to the center tap 244 of the two windings 245

SUBSTITUTE SHEET and 246 of the primary of a transformer 247 having a magnetic core, e.g., a ferrite core 248. The transformer 247 has a main secondary winding 249, which provides the output circuit of t±e inverter. A number of short winding secondaries later to be described are also provided. The free end terminal of winding 245 connects to a line 250. The free end terminal of winding 246 connects to a line 251. A capacitor 252, analogous to capacitor 60 in FIG. 6, is connected at one terminal to line 250 and at the other terminal to line 251. Line 250 also connects through diode

253 to transistor 255. Similarly line 251 connects through diode

254 to transistor 256. Transistor 255 has a base 257, a collector 258 to which diode 253 is connected, and an emitter 259. Transistor 256 has a base 260, a collector 261 to which diode 254 is connected, and an emitter 262. The bases are fed by a low voltage secondary 263 on core 248 of transformer 247, i.e., they are feedback windings of a very few turns, e.g. , two turns. Emitters 259 and 262 are connected together to the negative terminal 242 referred to above.

Lamps 264 and 265 are connected in series across the aforesaid output circuit of the inverter as also are lamps 266 and 267. A short secondary winding 268 on the core 248 of transformer 247 supplies heating current for filament 269 at a first end of lamp 264. Ballast for lamps 264 and 265 is provided by inductor 270 which is connected at one terminal to one terminal of secondary winding 249 and at the other terminal to the line connecting winding 268 to filament 269, as shown. Another short secondary winding 271 on core 248 supplies filament heating, current to filament 272 at the second end of lamp 264 and to filament 273 at a first end of lamp 265. A still further short winding secondary 274 on core 248 supplies filament heating current to filament 275 at the second end of lamp 266 and the filament 276 at the first end of lamp 267. An additional short

SUBSTITUTE SHEET winding secondary 277 on core 248 supplies filament heating current to t±e filament 278 at the first end of tube 266. Lamps 266 and 267 have a capacitor ballast 279 which is connected at one terminal to the line connecting winding 277 to filament 278 and at the other terminal to the same . terminal of secondary 249 as inductor 270. A final short winding secondary 280 connected at one end to the other terminal of secondary winding 249 and at the other end to filament 281 at the second end of lamp 267 and to filament 282 at the second end of lamp 265, putting these two filaments in parallel across the lines from winding 280. The operation of this circuit is clear in the light of the explanation of other inverter output circuits hereinabove and need not be repeated. The combination of inductor and capacitor ballasts in the circuit provide high power factor in t±e inductor output circuit.

The circuit illustrated in FIG. 14 may be modified to supply four lamps in parallel instead of two pairs of two series connected lamps in parallel. The inverter components and their connections to each other in the modified circuit are the same as the components of the inverter in the circuit of FIG. 14 and the modifications are in the connections of the four parallel connected fluorescent tubes. They are all connected in parallel to the secondary winding 249 in essentially the same way that t±e three parallel fluorescent tubes of FIG. 6 are connected to terminals 43 and 43a. In other words, a transformer like 54 of FIG. 6 is provided with a secondary winding like 249 in FIG. 14 which is connectd at one terminal to a winding like 92 and the four filaments at the end of the lamps supplied by a single short winding like 92, and at the other terminal to the four filaments at the other end of the lamps which have individual short secondary windings. Thus, one terminal of secondary winding is conencted in parallel to each of two tubes through a ballast

SUBSTITUTE SHEET ^&ito&_\ϋ& inductor to the filament circuit including a short winding secondary like 268 of FIG. 14 and to t±e end of t±e other two tubes through a ballast capacitor to the filament circuit including a short winding secondary like 277 of FIG. 14. The connection of a single short winding like 92 of FIG. 6 and 280 of FIG. 14 is to each of the filaments at t±e other end of the four lamps in parallel, as t±e filaments of t±e three lamps in FIG. 6 are connected to the winding 92. Operation of this circuit is obvious from the descriptions of output circuits of inverters hereinabove. Again the combination of inductor and capacitor ballasts in the inverter output circuit for the tubes, as described, assures high power factor in the output circuit.

A further modification of the circuit of FIG. 14 is to add starting aids for the two pairs of series connected fluorescent lamps. The starting aids are two capacitors, one connecting filament circuit 268 to filament circuit 271 and inductor 270 and the other connecting filament circuit 274 to filament circuit 277 and capacitor 279. These starting aids have the characteristic of reducing the starting voltage required to strike the arc between the cathodes (filaments) at the first and second ends of t±e lamps.

FIG. 15 depicts a dimming circuit which comprises an inverter like the inverter of FIG. 14 and a different inverter output circuit. Components in the circuit of FIG. 15 have been given the same reference numbers as corresponding parts in the circuit of FIG. 14 with a postscript c. The output circuit of FIG. 15 includes three fluorescent lamps 264c, 265c and 266c, lamps 264σ and 265c being connected in series and that combination being connected in parallel with lamp 265σ across the terminals of secondary winding 249c of t±e inverter transformer 247c. The series connected lamps have a capacitor ballast 279c between the line connecting short winding 268σ with filament 278c and the

EET terminal of secondary winding 249c. The parallel lamp 266c has an inductor ballast 284 between t±e line connecting short winding 277c with the filament 278c of lamp 266c and the terminal of secondary winding 249σ. 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 is provided comprising in series a primary winding 290 of a saturable reactor 291 having a magnetic core 292, e.g., ferrite, and a variable resistor 293 connected to the DC terminals 241c and 242c or other source of direct current. The secondary of reactor 291 is a short winding 294 having one terminal connected by line 295 to a capacitor 297 connected to t±e line connecting short winding 268c with filament 278c, and to an inductor 298 on core 292 connected to t±e line connecting short winding 277c with filament 278c of lamp 266c.

Ballast capacitor 297c 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 t±e variable resistor 293 of by other equivalent means. In this manner, t±e light intensity may be changed in response to varying needs.

In all of the inverter circuits a small condenser may be used to connect either the line from the positive DC terminal (line 62 in FIG. 6 and the corresponding line in other figures) or the line to t±e negative DC terminal (line 69 in FIG. 6 and the corresponding line in other figures) to the lamp fixture metallic structure (ground) which enables the ballast to pass the U.S. specifications of Underwriters Laboratories for safety in terms of fixture leakage current.

High frequency current can flow or leak through the primary-to-seσondary capacitance of the main inverter transformer 54 and on through the unavoidable lamp-to-fixture capacitance to the fixture itself. The added capacitor provides a short, local path for this leakage current to return to its point of origin (the primary winding) without leaving the fixture.

A further useful modification of the inverter circuit limits transistor collector voltages without t±e use of a Zener diode. Referring to FIG. 13, this modification involves moving conductor 76d from its location in series, effectively, with the positive DC input line 62d and connecting it in series, effectively, with the negative line 69d. Specifically line 69d is broken between t±e points of connection to capacitor 81d and emitter 48d and inductor 76d is connected between these points and Zener diode 85d is emitted. Also two ordinary diodes are added so both of their anodes connect to negative input terminal 42d. The cathode of one of the added diodes is connected to a tap near the mid-point of primary winding 52d and the cathode of the other diode is connected in symmetrical way ^* to a tap near the mid-point of primary winding 53d on transformer 54d. With this modified circuit, whenever excess voltage appears at t±e collector of either transistor, t±e above mentioned tap on the primary winding connected to the other transistor will go negative turning on one of t±e added diodes and connecting the constant DC input voltage across the portion of the primary winding between the center tap 57d and the top point to which the added conducting diode is connected. Thereafter the voltage cannot rise any higher on any winding on transformer 54d. Excess energy stored in inductor 76d is, by the means, returned to the DC power supply instead of being dissipated in the Zener diode or transistors. With this altered location of inductor 76d, the winding 78d on t±e same core 66d

OMPI

^«^NAΪI^ need not be an additional winding but can be an extension of winding 76d. This simplifies construction by reducing (by one) the number of terminals needed for 76d and 78d and by avoiding the need to insulate those windings from each other.

The circuits of the invention, and in particular the electronic ballast circuits, have great benefit, to the utility industry because of their 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 discussed in t±e section dealing with the background of t±e invention. 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 t±e 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.

SUBSTITUTE SHEET The inverter may be described as a symmetrical, class B, push-pull, current-limited, transistorized oscillator with switched higher and lower feedback windings, it is self-starting, highly efficient and stable over a wide range of input 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 disclosure and claims without departing from the principles of t±e invention disclosed.

Having thus described and illustrated the ionvention, what is claimed is:

J REA T

OMPI

SUBSTITUTE SHEET ^m&_f

Claims

1. An electronic ballast for gas discharge lamps which comprises inverting means including input terminals for receiving and inverting DC from a supply thereof into high frequency AC and delivering said AC to output terminals, characterized by said inverting means being a symmetrical, class B, push-pull, current-limited, dual feedback oscillator and said high frequency AC being at proper voltage to provide the necessary starting voltage for gas discharge lamps to be connected to said output terminals, and ballasting means for such gas discharge lamps.

2. An electronic ballast for gas discharge lamps as set forth in claim 1 characterized by said inverting means comprising two transistors, a transformer having a primary winding connected to the collectors of said transistors; two secondary feedback windings on said transformer, one of them being relatively high voltge, center tapped, connected at each end through a relatively slow diode to the base of a different transistor, and the second feedback winding being relatively low voltage connected to the bases of said transistors through a circuit including resistance means.

3. An electronic ballast for gas discharge lamps as set forth in claim 2 further characterized by including two catching diodes, one connected at one terminal to the junction of one side of the higher voltage feedback winding and its slow diode and at the other terminal to the junction of the collector of the adjacent transistor and the transformer and the other catching diode being connected at one terminal to the junction of the other side of the higher voltge feedback winding and its slow diode and at the other terminal to the junction of t±e other side of the higher voltage feedback winding and its slow diode and at the other terminal to the juction of the collector of the other transistor and the

SUBSTITUTE SHEET transformer.

4. An electronic ballast for gas discharge lamps as set forth in claim 1 characterized by said means for inverting further comprising an inductor having a magnetic core for maintaining substantially constant direct current through the circuit of said means for inverting DC into high frequency AC and a second inductor on said magnetic core for maintaining substantially constant base current drive.

5. An electronic ballast for gas discharge lamps as set forth in claim 1 which is charactrized by including a DC supply means.

6. An electronic ballast for gas discharge lamps as set forth in claim 5 which characterized by said DC supply means being a battery.

7. An electronic ballast for gas discharge lamps as set forth in claim 5 charactrerized by said DC supply means beiong a solar cell.

8. An electronic ballast for gas discharge lamps as set forth in claim 5 characterized by said DC supply means being a rectifier.

9. An electronic ballast for gas discharge lamps as set forth in claim 8 characterized by the rectifier including asingle phase diode bridge.

10. An electronic ballast for gas discharge lamps as set forth in claim 8 characterized by the rectifier including (i) a tansformer having a delta connected primary winding adapted to be supplied with three phase current of any commercially available voltage, phase and frequency and (ii) a six-phase secondary inductively connected thereto.

11. An electronic ballast for gas discharge lamps as set forth in claim 1 characterized by said gas discharge lamps being fluorescent tubes and said electronic ballast including a plurality of electrical connecting means adapted to be connected to said output terminals for holding fluorescent tubes.

12. An electronic ballast as set forth in claim 11 which is further characterized by said ballasting means being electrically connected to said output terminals and being capable of ballasting a tube in each said electrical connecting means.

13. An electronic ballast as set forth in claim 12 charcterized by including either an inductor, a capacitor or both and inductor and a capacitor.

14. An electronic ballast as set foth in claim 11 which is further characterized by comprising a transformer hving a primary connected to said output terminals and a secondary connected to a load, said secondary having only inductive coupling to said primary.

15. An electronic ballast as set forth in claim 1 characterized by being combined with a high frequency AC lighting system, said lighting system including rectifying means having (i) AC input terminals adapted to be connected to a source of AC power of commercial voltage and frequency, and (ii) DC output terminals constituting said DC supply connected to said output terminals for receiving DC, electrical connecting means for receiving high frequency AC from the output terminAls of said inverting means, and lamp receiving means adapted to hold at least one gas discharge lampoand connect each such lamp to said electrical connecting means.

16. An electronic ballast as set forth in claim 15 characterized by said rectifying means including voltage transforming means ahead of said AC input terminals for transforming AC from said source of AC power to proper voltage for said commercial frequency AC distribution facilities, said facilities including at. least one of (a) single phase output terminals, (b) three phase output terminals and (c) six phase output terminals.

^ r^

17. An electronic ballast as set forth in claim 15 characterized by said rectifying means including AC ooutput terminals adapted to be connected to commercial frequency AC distribution facilities, means is a capacitor.

18. An electronic ballast as set forth in claim 16 characterized by said voltage transforming means having a three phase primary winding and a secondary comprisig six windings, each of said six windings having (a) one end connected to a common center and said center electriclly connected to a neutral output terminal, and (b) the other end of each of said windings being connnected (i) to diode means for conducting positive current to a positive outlet terminal, and (ii) to diode means for conducting negative current to a negative output terminal.

19. An electronic ballast as set forth in claim 1 characterized bu being combined with a high frequency AC lighting system, said system including a centrally located rectifying means, a plurality of lamp receiving means connected to said ballasting means, each lamp receiving means being a fixture adapted to hold and supply high frequency AC to at least one fluorescent tube, and said inverting means being supplied with DC from said centrally located rectifying means.

20. An electronic ballast as set forth in claim 19 characterized by said inverting means being associated with and serving a plurlity of adjacent removable fluorescent tubes.

21. An electronic ballast as set forth in claim 19 characterized by said system further including a transformer having a polyphase primary adapted to be connected to a commercial source of polyphase AC and a six phase star secondary connected to diode rectifying means with positive current connected to a positive output terminal and a negative current to a negative output terminal for supplying said DC to said inverting means.

22. An electronic ballast as set forth in claim 2 characterized by being combined with a high frequency lighting means including receiving means adapted to hold at least one fluorescent tube having electrodes at each end thereof connected to a filament and in which said trnsformer has a high frequency magnetic core, and which further comprises a secondary high frequency winding on said core, and means for conecting said heater windings with the filaments in said fluorescent tube.

23. An electronic ballast as set forth in claim 22 characterized by a further transformer including a primary winding receiving its excitation from vvoltage across a fluorescent tube, and said heater windings being inductively coupled to said primary winding, whereby the filament current is reduced automatically with reduction in said lamp voltage after arc current in said tube is estab ished.

24. An electronic ballast as set forth in claim 19 characterized further by comprising means adapted to vary the current through a fluorescent tube.

25. An electronic ballast as set forth in claim 2 characterized by being combined with a high frequency AC lighting system, said system comprising (A) rectifying means to receive and convert commercially available AC to DC and supply it to said inverting means, (B) electrical connectig means connected to said transformer to receive said high frequency AC, and (C) lamp holding means adapted to hold at least one gas discharge lamp having electrodes in contact with said electrical contacting means.

26. An electronic ballast as set forth in claim 25 characterized by the system including a plurality of said inverting means, a plurality of said electrical connecting means, and said ballasting means limits the current flowing in each lamp when connected to said electrical connecting means.

SUBSTITUTE SHEET

27. An electronic ballast as set forth in claim 15 characterized by said six-phase secondary having a grounded neutral common to the AC and DC parts of said system.

28. An electronic ballast as set forth in claim 19 characterized by said lamp fixture being connected to t±e lamp receiving means in another fixture by only two wires.

29. An electronic ballast as set forth in claim 25 charactrerized by the inverting means further comprising secondary heater windings on said transformer adapted to make electrical connection with filaments in lamps held in said lamp holding means.

30. An electronic ballast as set forth in claim 29 characterized by the transformer primary for said secondary heater windings being across a lamp whereby relatively high current flows through the filaments before an arc is struck and relatively low current flows through the filaments after an arc is struck.

31. An electronic ballast as set forth in claim 29 characterized by further including means for varying t±e current flowing through a lamp during operation thereof.

32. The invention substantially as described and illustrated.

SUBSTITUTE SHEET