US2644107A - Preheat neutralizing circuit for fluorescent lamps - Google Patents

Description

June 30, 1953 KElFFER ETAL 2,644,107

7 PREHEAT NEUTRALIZING CIRCUIT FOR FLUORESCENT LAMPS Filed Nov. 25. 1949 2 Sheets-Sheet l 1 f2 /Z I I? lnven kors: Raymond L. Kei=f-+er1 B we Lemmers, b5 W Their" A'iriorneg.

June 1953 R. 1.. KEIFFER ETAL 2,644,107

PREHEAT NEUTRALIZING CIRCUIT FOR FLUORESCENT LAMPS Filed Nov. 23, 1949 2 Sheets-Sheet 2 Fig 4. /Z

i i; 1.2 Lamp 4- -17 Lead Lamp 6" Q Irwervcors: Raymond L. KePF'f'er,

fjgene 'Lemmers, 9 MC" Their At'korneg.

Patented June 30, 1953 PREHEAT NEUTRALIZING CIRCUIT FOR FLUORESCENT LAMPS Raymond. L. Keifier, Chagrin Falls, and Eugene Lemmers, Cleveland Heights, Ohio, assignors to General Electric Company, a corporation of New York Application November 23, 1949, Serial No. 129,158

This inventionrelatesgenerallyto starting and operating circuits for electric discharge devices such as fluorescent lamps, and more particularly to a new and improved switchless circuit and transformer structure for preheating the filamentary electrodes of such lamps at starting, and for eliminating the heating current after the discharge has started within the lamps.

Circuits presently in commercial use for operating fluorescent lamps are-generally provided, either with switching means to allow preheating of the lamp electrodes to an'electron-emitting temperature, or with high voltage high leakagereactance transformers to start the lamps directly without any preheating of the electrodes. The first method of operation necessitates an undesirable delay in starting the lampafter the initial application of voltage to the circuit, and often results in undesirable flickering when the lampfails to start on the first attempt; the second method places considerable electrical stress Claims. (Cl. 315===95) on the lamp electrodes which, other factors being equal, results in a shorter lamp life.

In our copending United States application No. 731,488 (Lemmer-s and Keiff'er), filed February 28, 194"], now U. S. Patent 2,504,549, assigned to the same assignee as the present invention, there is disclosed a circuit for impressing heating voltages across the filamentary electrodes of a fluorescent lamp at'starting, which circuit comprises three windings per electrode for neutralizing these voltages through changes in phase and magnitude of currents through a transformer consequent upon conduction in the lamps.

The present invention utilizes basically the same principles as described in the aforementioned application, and is concerned withan improved and more economical circuit and transformer structure for electrode preheating and subsequent neutralization in a like manner, wherein the number of windingsper electrode is substantially reduced.

Accordingly, it is an object of our invention to provide an improved and simplified circuit for switchless starting and operation of fluorescent lamps, which permits the application of heating voltages to the filamentaryelectrodes of such lamps previous to st-artingand which, immediately upon initiation of a'discharge within said lamps, discontinues said heating voltages by means of changes in the phases and magnitudes of'their components seats to substantially neutralize them.

Another object of our invention is to provide an improved circuit for effecting the first-mentioned object and which, in addition, is well adapted to'extension'to any number. of lamps by the simple expedient of multiplying the windings on an auxiliary transformer.

A further object of our invention is to provide a circuit which, in additionto fulfilling the previously mentioned objects, is particularly adaptable to certain modifications for providing a starting voltage to an auxiliary electrode, which starting voltage is likewise neutralized after the lamps have started, in the same manner as the heating voltages.

For further objects and'advantages and for a better understanding'of our invention, attention is now directed to the following description and to the accompanying drawings. The novel features of our invention will be more clearly pointed out in the appended claims.

In the drawings:

Fig. l is'a schematic diagram of a starting and opera-ting circuit for a pair of fluorescent lamps embodying our invention.

Figs. 2'and 3 are vector diagrams for the purpose of illustrating the voltage relationships in the windings of the transformer of Fig. 1, under starting and operating conditions, respectively.

Fig. 4 is aschematic diagram of a modified form of our neutralizing circuit as applied to a low reactance transformer of well known design.

Fig. 5 is a diagrammatic representation of a transformer structure embodying certain featuresof my invention.

Referring to Fig. 1 there is shown a pair of electric discharge devices I, I such as fluorescent lamps, which will be referred to henceforth as the lag lamp and the lead lamp respectively. These lamps comprise elongated tubular or cylindrical envelopes 2, 2', which have sealed into their ends filamentary electrodes 3, 4, and 5, 6, respectively. These electrodes may be constituted by coils of tungsten wire activated with oxides of alkaline earth metals, such as barium and strontium oxides. The envelopes 2, '2' contain rare gases such as krypton, neon, argon, or mixtures thereof, at a pressure of'a few millimeters, and a small quantity of mercury. The devices I, I may be low pressure, positive column lamps of the fluorescent type, provided with a suitable phosphor coating. This fluorescent coating, upon excitation by the radiation produced by an elec tric discharge between the electrodes, transforms a short wave length radiation due to the dis charge, into a longer wave length radiation occurring within the visible range.

The lamps l, i are connected in a lagging power factor load circuit 1, B and a leading power factor load circuit 9, 8, respectively, which circuits are connected across a suitable source of potential. In the drawings; we have illus trated a voltage step-up autotransformer ill, comprising a primary winding ii and a pair of secondary windings l2 and i3. The secondary windings are loosely coupled to the primary winding and have considerable leakage react" ance; such a structure is relatively well known in the art, and permits utilization of the secondary windings both as voltage step-up windings, and as ballast reactances for limiting the discharge current through the lamps. The lag lamp is connected directly through conductor 1 to secondary winding l2, whereas the lead lamp is connected through its conductor 9 to winding [3, in series with a capacitor [4 which performs the usual function of inverting the total reactance in this part of the circuit from inductive to capacitive.

In accordance with the principles disclosed in our application No. 731,488, voltages for heating the filamentary electrodes of the lamps may be provided by means of three sources, these sources having predetermined phase relations which change upon the initiation of a discharge through the lamps. In the above-mentioned application, we have shown three teritary windings, coupled to the three windings of autotransformer 12, for each of the four filamentary electrodes. In other words, three tertiary windings are required for each lamp electrode so that for the two lamps illustrated herein, four groups of three tertiary windings, that is, a total of twelve teritary windings are required.

In accordance with our present invention, the number of tertiary windings is greatly reduced. Associated with each winding of autotransforrner I is a single tertiary winding, these tertiary windings being l5, l6, and H for windings ll, l2, and [3, respectively. The three tertiary windings are connected in series across the primary winding [8 of an auxiliary transformer iii, which transformer will be referred to henceforth as the cathode heating transformer. Transformer 19 may be of conventional construction, and is provided with as many secondary windings as there are filamentary electrodes which it is desired to heat. As illustrated herein, transformer I9 is provided with secondary windings 20, 2|, 22, and 23 for electrodes 3, 4, 5, and B, respectively.

The turns of the tertiary windings in autotransformer l2 are so proportioned that a result voltage is impressed across primary iii of cathode heating transformer l9 at starting of the lamps, and this voltage is substantially neutralized after a discharge has started in the lamps. It will be obvious to those skilled in the art that it is thereafter a relatively simple matter to design cathode heating transformer IS to have the secondary windings thereof transform the applied voltage to any desired value of volt age for heating the lamp electrodes, or for performing other functions.

Referring to Figs. 2 and 3, the vector diagrams therein illustrate the phase and magnitudes of the voltages in the tertiary windings of autotransformer i2, Fig. 2 being applicable to the voltage existing before starting, and Fig. 3 being applicable to voltages existing during lamp operation.

When the supply voltage is initially applied across primary winding ll of autotransformer it, the induced voltages in secondary windings l2 and it are practically in phase with the voltage existing across the primary winding, and there is no discharge current circulating through windings I2 and [3 to disturb these phase relationships. Accordingly, the voltages induced in tertiary windings I5, 15, and I? are in like phase and may be represented by vectors V15, V16, and Viv, respectively. These voltages add up to produce the resultant V7 which has a mag nitude, after conversion through the cathode heating transformer I9, sufiicient to cause heat ing of the filamentary electrodes in the lamps.

After the lamps have attained an electronemitting temperature, the arc or discharge strikes within them; and the phases of the currents through the secondary windings i2 and H are respectively retarded and advanced. This is due to the fact that the leakage reactance of winding l2 introduces an inductive reactance in series with lag lamp I, whereas capacitor [4 introduces a capacitive reactance in series with lead lamp l which overcomes the leakage reactance of secondary winding 13. The phases of the voltages induced in tertiary windings l6 and I! are retarded and advanced respectively in the same fashion as the currents through secondary windings I2 and I3, and the voltage induced in tertiary winding l5 naturally remains unchanged. Accordingly, the voltages in the tertiary windings may be represented by vectors V15, V16, and V17, of fig. 3 and these now add up vectorially to produce a resultant Vrcf substantially diminished magnitude.

In practice, complete neutralization is diflicult to obtain because of the potential drop in the filamentary electrodes of the lamp produced by the arc or discharge current; the resultant voltage Vr', however, is small enough to be negligible. In fact, perfect correlation between the magnitudes and phases of the voltages in the tertiary windings to obtain substantially zero resultant voltage during lamp operation is not necessary for the successful operation of the circuit, and a small amount of residual electrode-heating current is often desirable in order to lower the cathode voltage or are drop.

Referring once more to Fig. 1, there is shown, in cathode heating transformer 19, an auxiliary secondary winding 24, illustrated in dotted outline. This winding may be utilized, if desired, to provide a starting voltage to a pair of auxiliary electrodes 25, 25' in the lamps. These electrodes may be constituted by stripes of conductive metallic paint applied to the surfaces of envelopes 2 and 2 of lamps l, l, respectively. The uses and principles of operation of such auxiliary starting electrodes are well known in the art and need not be described except to state that they permit a lowering of the starting voltage required across the main electrodes. It will be apparent that by obtaining the auxiliary starting voltage from cathode heating trans former I9 in accordance with our invention, the starting voltage is removed from the stripes or auxiliary electrodes as soon as the discharge is started within the lamps. This is due to the fact that the starting voltage is neutralized in exactly the same fashion as the heating current to the filamentary electrodes. This is a noteworthy feature since it is generally advantageous to remove high voltages from circuits with which operating personnel may come into contact.

.Although the circuit has thus far been described. referencetosxa highleakage reactance type of transformer, wherein. the-.balla-sti-n action. required. for ,rlimiting the: discharge current. through the. lamps; iss providedv by the secondary windings: of. the step-up transformer; the circuit is equally applicable to a: low reactance type ofastep-up transformer. Such a circuit is illustrated iii-Fig. a, whereinlsimilar reference numerals refer to corresponding elements. Thus, referring to Fig; .4, step-up autotransformer Hi comprises, as before, apri'mary winding II, but this winding is now, continued intov a tightly coupled section H. which providesa voltage step-up action. Connected tothe outer end of section I lare separate ballasting reactances t2 and It, reactance l2 beingconnected directly, and rea-ctance t3 being connected. through theusual phase advancing capacitor Mp The electrode heating andneutraliz-in-g windings l5, l6, and I! are coupled to windings II, It, and. I3, respectively, the remainder of the circuit being in all other, respects similar to that of-qFig. 1-.

The 'loperation of this c-ircuitis likewise similar to that of Fig. 1. The voltage for heating the lamp electrodes at starting is generated winding 15. After the discharges have started, the voltages induced in windings l6 and I! by the discharge current' fiowing through ballast reactances l2 and. I3 add vectorial-ly to the voltage induced in winding ii to produce a resultant of substam tiallyzero magnitude, thereby neutralizingthe electrode heating. 'Cathodeheating transformer l9provides the required transformationforapplying the resultant of the induced voltages to the various lamp electrodes.

Fig. his a diagrammatic representation of a transformer, similar to that described in appli= cation No. 690,855 of Charles W. Kronmiller, filed August 16,, 19416, and assigned to the same assignee as the present invention. The transformer herein is adapted to provide the windings required by the circuit of Fig. "I, and similar re er= ence numerals refer to corresponding circuitelements. Transformers Hi and Id comprise'a'com mon core 26; the transformer structure built upon core 26 to the right of section line 21-2? consti= tutes transformer l6, while the structure to the left of the section line constitutes transformer 19. Primary winding H and secondary winding l2 and 13 are mounted in separate slots in core members 28 and 28; and tertiary windings l5, l6, and H are likewise mounted in these slots in close coupling with their associated main windings. Air gaps 29, 30, and 3! provide the desired leakage reactance between main windmgs.

The windings I8, 20, 2!, 22, 23, and 24 of trans= former H! are mounted in a slot in core members 32 and 32'. An air gap 33 provides the necessary magnetic decoupling between transformers l9 and 10. It is to be understood that this particular transformer structure is given simply by way of non-limitative illustration; and, obviously, separate transformer structures may be utilized if desired.

While certain specific embodiments have been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. Thus, it will be obvious that the circuit may be modified to include any number of lamps by providing two additional secondary windings for the electrodes of each additional lamp. Likewise, whereas we have shown particular circuits comprising a stepup autotransformer, it will be evident that other circuits which produce likeresults may be used in lien or the one which has been: illustrated by adding: tertiary windings. to it in! the manner de scribed in our invention. :Theappended claims are, therefore, intended to cover any such modifications coming within the true spirit and scope of the. invention.

What we claim as new and desireto secure by Letters Patent of. the United States is: I

1'. Apparatus'for starting and operating electric discharge devices of the type including a pair of thermionicelectrodes, comprising; a primary inductance adapted for connection to an alter mating-current supply, and a pair of secondary inductances connected to said primary inductance for limiting the currentsupplied toalaggi-ng and to -a leading power-factor load circuit each illeludingone of said devices; three tertiary windings, separate onesof. said tertiary windings being coupled tosaid primary and secondary inductances; said tertiary/windings being connected in series and poled for producing a resultant voltagethe magnitude of which varies with the cunrent conducted by said secondary i-nductances, and auxiliary transforming means comprising a primary winding connected across said.- tertiary windings in series and also including a plurality of secondary windingsadapted to be connected to the electrodes of said discharge devices for providing heating current thereto.

2. Apparatus for starting and operating electric discharge devices of the type including a pair of thermionic electrodes, comprising: a magnetic core structure having'wound thereon a primary winding adapted for connection to an alternating currentsupply, and a pair of secondary windings inductively coupled to said primary winding with high leakage reactance in said core structure therebetween, and connected to said primary winding for limiting the current supplied to a lagging and to a'leading power factor load circuit each including one of said devices; three tertiary windings'separate ones of said tertiary windings being coupled to said primary and secondary windings, said tertiary windings being connected in series and poled for producing a resultant voltage the magnitude of which varies in accord= ance with the current conducted by said secondary windings; and auxiliary transforming means comprising a primary winding connected across said tertiary windings in series, and a plu= rality of secondary windings adapted to be con= nected to the electrodes of said discharge devices for providing heating current thereto.

3. Apparatus for starting and operating electric discharge devices of the type including a pair of thermionic filamentary electrodes, comprising: a magnetic core structure having wound thereon a primary winding for connection to an alternating current supply, and a pair of secondary windings connected to said primary winding, and inductively coupled thereto with high leakage reactance in said core structure therebetween for limiting the current supplied to a lagging and to a leading power factor load circuit each including one of said devices; three tertiary windings, re spective ones of said tertiary windings being inductively coupled to said primary winding and to said secondary windings, the tertiary winding coupled to said primary winding producing a reference voltage, and the tertiary windings coupled to said secondary windings producing components of voltage variable in magnitude and phase in response to currents conducted by said secondary windings, said tertiary windings being connected in series and poled so that the resultant of said reference voltage and said components is reduced upon the flow of current through said secondary windings; and an auxil iary transformer comprising a primary winding connected across said tertiary windings in series for receiving said resultant voltage, and secondary windings coupled thereto for converting said resultant to voltages of desired amplitude adapted to be applied to the electrodes of said discharge devices for providing heating thereof at starting.

4. Apparatus for starting and operating electrio discharge devices of the type including a pair of thermionic filamentary electrodes and an aux= iliary starting electrode, comprising: a magnetic core structure having wound thereon a primary Winding for connection to an alternating current supply, and a pair of secondary windings con nected to said primary inductance, and coupled thereto with high leakage reactance in said core structure therebetween for limiting the current supplied to a lagging and to a leading power factor load circuit each including one of said devices; three tertiary windings, respective ones of said tertiary windings being inductively coupled to said primary winding and to said secondary windings, the tertiary winding coupled to said primary winding producing a reference voltage, and the tertiary windings coupled to said sec ondary windings producing components of volt age variable in magnitude and phase in response to the currents conducted by said secondary windings, said tertiary windings being connected in series and poled so that the resultant of said reference voltage and said components is reduced upon the flow of current through said secondary windings; and an auxiliary transformer com= prising a primary winding connected across said tertiary windings in series for receiving said re sultant voltage, secondary windings coupled thereto for converting said resultant to voltages of desired amplitude adapted to be supplied to the electrodes of discharge lamps for heating thereof at starting, and an auxiliary winding coupled thereto for converting said resultant to a voltage of desired amplitude adapted to be applied to said starting electrodes.

5. A transformer structure comprising: a magnetic core, primary and secondary windings on said core, said windings being loosely coupled by means of a leakage flux path therebetween; connection linking said windings in autotransformer relation for providing a relatively high open circuit voltage and a relatively low operating voltage when load currents flow therethrough to associated leading and lagging circuits for operating discharge devices of the filamentary electrode type; three tertiary windings mounted on said core, separate ones of said windings being closely coupled respectively with said primary and secondary windings, said tertiary windings being connected in series andpoled to produce a resultant voltage the magnitude of which decreases with the current conducted by said secondary windings; and auxiliary windings mounted on said core, said auxiliary windings being relatively decoupled from previously mentioned windings by means of high leakage flux paths, said auxiliary windings comprising an auxiliary primary winding connected across said tertiary windings in se ries for receiving a resultant voltage having a substantial value when no load current flows in said primary and secondary windings and having a lesser value when load currents flow therein, and auxiliary secondary windings closely coupled to said auxiliary primary winding for converting said resultant voltage to voltages of predetermined amplitude for application to the electrodes of said devices to provide heating thereof.

RAYMOND L. KEIFFERi EUGENE LEMMERS.

References Cited in the file of this patent, UNITED STATES PATENTS Number

Images