US2429162A - Starting and operating of fluorescent lamps - Google Patents

Description

Oct. 14, 1947.

R. w. KEISER, ETAL' STARTING AND OPERATING OF FLUORESCENT LAMPS Filed Jan. 18, 1943 3 Sheets-Sheet- 1 a /7 P a V 4 p5 7 --z a \g T gvwoz/wlkw Oct, 14, 1941' R. w. KEISER ET AL I 2,429,162

STARTING AND OPERATING OF FLUORESCENT LAMPS Filed Jan. 18, 1943 s Sheets-Sheet 2 1 ,1947. R. w. KEISER EIAL STARTING AND OPERATING OF FLUORESCENT LAMPS 3 Sheecs-Sheet 3 Filed Jan. 18, 1943 Patented Oct. 14, 1947 STARTING AND OPERATING OF FLUORESCENT LAMPS Russell William Keise r and Charles Philippe Boucher, Fostoria, Ohio, assignors to Boucher and Keiser Company, Atlanta, Ga., a partner ship Application January 18, 1943, Serial No. 472,768

I 13 Claims.

This invention relates to fluorescent lamps and more particularly to circuits and apparatus for starting and operating such lamps from normal sources of power supply.

It is a general object of the present invention to provide novel and improved apparatus and circuits for cold cathode starting and normal operating one or more lamps of the fluorescent type from a commercial source of alternating current.

More particularly it is an object of the invention to provide circuits and apparatus capable of providing the necessary excess potential for the cold cathode starting of lamps of the fluorescent type and for subsequently providing the exact operating potential and current for the normal lighting of these lamps.

It is an important object of the invention to provide the additional lamp starting potential without using any increased quantity of copper or iron above that necessary to provide the normal operating voltage and current for the lamps under optimum conditions.

It is an important feature of the invention to provide a transformer, adapted to be interposed between a normal source of alternating current at commercial potential and one or more lamps of the fluorescent type whereby for regular operation of the lamps a suitable potential and current is provided, together with automatic means to temporarily give an increased turns-ratio between the primary and secondary of the transformer for supplying a substantially higher potential available to start the lamps by the cold cathode method.

Another important feature of the invention consists in the switching arrangement, which, under cold lamp conditions so associates the parts of the circuit, that, upon closing the main power switch a high starting potential is applied to the lamps and is automatically reduced upon lighting of the lamps to that necessary for their normal operation.

An additional object of at least one embodiment of the invention consists in the automatic switching of current limiting resistors into the lamp circuits during the starting operation to limit the arc currents to values low enough to ensure against damage to the filaments of lamps built for hot cathode starting but used in accordance with the present invention for cold cathode starting.

A still further object of that particular embodiment includes delayed action switching which is timed to occur when the filaments of the electrodes have obtained a proper emissive temperature as a result of the action of the striking are,

Figure 1 is. a schematic and diagrammatic showing of a circuit and apparatus for starting,

and operating a pair of fluorescent lamps from a conventional source of alternating current, making use of a heat actuated switching device for effecting the voltage changes.

Figure 2 is a View similar to Figure 1 but show ing a relay type magnetic switching device;

Figure 3 is a view similar to Figure 1 but showing a modified thermal type of starting switch;

Figure 4 illustrates a circuit in which the reactances normally used for regulating the current flow to the several lamps are combined with the secondaries of the transformer; V

Figure 5 shows a further embodiment of the invention;

Figure 6 shows a still further embodiment for the operation of a plurality of lamps;

Figure '7. is a diagrammatic arrangement of a core structure which may be used when magnetic shunts are indicated in the transformer magnetic circuits; and

Figure 8 illustrates a further embodiment of the invention incorporating delayed action switching from starting to operating conditions together with automatic current limiting features active only during the starting operation.

With the increasing use of fluorescent lamps for general lighting purposes there has been an insistent demand for an improved system for starting such lamps, since the ones in vogue at the present time interpose too much delay between the closing of the power switch and the actual striking of the are which causes the illumination in the, lamp.

Most lamps are now lighted by making use of starting systems involving the filaments in the two ends of each lamp which are first heatedto incandescence after which a high potential resulting from a reactance kick'following a circuit change is relied on to establish the arc. Certain automatic starting switches are provided which first connect the two filaments in series into the power source until they become adequately heated, After a certain time delay the starting ments of a potential much higher :than the 'normal operating potential, and as soon :as .the arc is struck, this voltage is reduced to just the requisite amount to maintainzthat.characteristic of are which will provide theidesiredjlight emission from the lamp as well as the'length of life commensurate with that provided by the use of the previously described type-of starting-operation.

It has heretofore been proposed to start fluorescent type lamps by the useof high potentials withcoldcathodes, but these systems have either failedtoproperly reduce the voltagefor normal operation, whereby the life .of the lamp was shortened, .o'r .h'avenecessitated the use of too great. .quantitiesof copper-and 'ironin the startingand operating apparatus. .In accordance with thepresent inventiona minimum use is made of these critical .inater 'ls and ;no additional .material, above that required for normal operation, is=inc1udedin the apparatus .in-spite of its ability to provides .high .striking .voltage for starting purposes. l

eierringfirst to Figure 1 ior oneembo'diment -.of the invention, there .is illustrated a pair of conventional fluorescent lamp .tubesJfl and H .each havingend laments l4 (each of which is connectedtoa -p1ai-r.of vpinilliiat .one end of the .tube. These pins are connected together, as

shown in accordance .withthepresent jinvention,

sothat thefilaments. are individually, shorted and -actsolelyras electrodes. ZITolimit the current supplied to thefiu'o'rescent type lamps, which have what is known as fnegative resistance, suitable reactors it and-l] are associated withthelarnps.

Where two similar lamps are simultaneously lighted on one circuit it is preferred to use a dual form of reactor such as illustrated in the co- ;pending application ofBussellWJKeiser, Serial Y9.- filed May 29,1342, for .Reactances, which issued October 30, .1945asi1lnited States Patent No. 2,387,797, in which the ,two windings :such-as J5 and ll are mounted on a single core provided with appropriate air gaps to produce high leakage reactance. .Obviouslythelamps are eonnected in Parallel so that .either one alone could be independently operated if desired without unbalancing the system,

O.neend ofone of the windings i6 is directly connected byeonductor [8 to one end of the tube [0, .while the other winding 11 has one end con- ..n ctediby conductor .[9 ,toone end .of tube H. A Qditable condenser .29 is interposed in the con- ..duc'to'r 19 to improve the power factor .of the whole circuit and obviate strobsoscopic efiects :from the lamps as is .welleknown.

The ivcommon terminal 2] of the two reactors 'i's connecte'd by wire 2,2 to one end 23 of the condarypfa special transformer and the opposite fend 2.4 of this secondary is connected by wire .25 to the rem ining terminals at the oppoaite ends .of both lamps.

y; ,In this embodiment the transformer is of the autoeconnected type, the full number of turns of Ithewinding between .;termin als 23 and 24 representing the secondary and a section. thereot bebecause tween terminals 24 and 26 representing the normal or operating primary. A source of alternating current, at a suitable commercial potential, is shown at 28 connected through a switch 29 and wire 30 to the terminal 26. In normal operation the terminal "24' is also connected to the source of power 28 through wire 3|, contact 32 of switch 33, movable contact 34 of this switch, and coniluctor 35. Under these conditions the turnsratio between the primary 24, 26, and the sec- :ondary .23, 25, is such as to provide the exact optimum operating potential from the source 28 to the :lamps, Ill. and ,1 I, the current being held to the predetermined proper amount by the design of the reactors I6 and I1.

For starting fluorescent lamps by the cold cathb'de'method a voltage at least 50% higher than that necessary or desirable for normal operation is required and in this embodiment of the invention it is provided by changing the turnsratio bet-ween the effective portion of the primary andthe secondary. Thismea'ns a reduction in the number ofturns on-the active section of the primary and for this-purpose atap is made at 3! and connectedby wire 38 to contact 39 of switch 33. Under the proper "positioning of the contacts in'the swith, as shown in the drawing, this connects the source 2-8 to the section 26, 31 of the primary, having les's'turns than the whole or'norm'al operating portion of the primary and of the now higherturns-ratio between secondary and primary an additional voltage is supplied to the lamps for striking the arcs and starting them. V

The switch illustrated at 33 is only one of a number of types suitable for changing from starting-to operating conditions. The switch shown is preferably enclosed in an evacuated bulb to reduce sparking or arcing and to thermally insulate a iii-metallic elemer'i't therein from the surrounding atmosphere. )The switch comprises three contacts 32, 34, and3 9 each carried on the end --of .a'long'arm. The supporting arm to for {the}: "ntact 134 is 'abi metallic element, and is initially "adjusted 'to close, the circuit between contacted andcontact 39 when the element '40 "is' lcold. This conditions the circuit for starting theflamps and'thearcs jump'through the lamps upon'closing the'swit'ch 29 becaus the curtailed "section of the primary is energized and produces ahigh secondary voltage. During this starting operation current flow to the primary is held to desired safe limits by-the resistor 42 interposed in conductor 38.

{The current flowing to the primary through "the bi-metallic'element '45, resulting from th operation of the two starting arcs is sufiicient "to heat the arm "40 and cause the contact 34 to moveover and engage contact 32. Since this is a relatively slow operation, it is desired to have contact 39 remain in engagement with contact '34 until the circuit 32, 34 is closed, thereby preventing extinguishing of the arc.

This is readily efiecte'dby having the supporting arm for contact '39 'otspring material and operating circuit and the arc will not be extinguished. The resistor 42 previously mentioned prevents a complete short circuit of that section of the primary between 24 and 3! while all contacts 32, 34, 39 are in engagement.

The starting operation is of extremely short duration so that the momentary overloading of both the primary and the secondary as well as the core of the transformer has no detrimental eifect so that this transformer can be designed to have only th requisite amount of both copper and iron to take care of its normal operating load. By using this system starting is achieved in an improved manner without the necessity of using any additional material in the system over that used for normal operation since the starting switch 33 need not be substantially larger than the usual starter, one of which is supplied with each lamp in the hot cathode starting system.

The circuit of Figure 2 does not difier substantially from that of Figure 1 and a detailed description of the whole circuit is not essential.

The main difference is in the switch which is of the magnetic type rather than the thermally operated type of Figure 1. It comprises a relay-like device having an operating coil or magnet 60 interposed in the conductor BI leading from terminal 24 of the secondary of the transformer to the left hand ends of both lamps. The armature 62 of the relay is connected by conductor 63 to the source of power 28 in the same manner as the bi-metallic arm of switch 33 while the opposite end of this source of power is connected to the primary terminal 26 of the transformer. The back contact 64 of the relay, with which the armature is in engagement when the magnet is unenergized, is connected through resistance 42 and wire 65 to the tap 3'! on the primary of the transformer. The front contact 65 of the relay is connected to the wire 6| which leads from the coil 60 directly to the terminal 24 of the secondary of the transformer.

In operation, with the parts in the position shown, a closing of the main switch energizes the section of the primary between the terminals 26 and 37 and produces a high secondary voltage which flows to the lamps striking arcs therein. When these arcs strike, current flows in the winding 60 from the secondary of the transformer, energizes the magnet and transfers the armature from the back contact 64 to the front contact 66 so that current from the source 20 is transferred from the tap 37 on the primary to the terminal 24 thereof. There is always a holding current which flows in the magnet 60 to maintain it in operating condition as long as the lamps are lighted. The contacts of the relay may either be arranged, in any Well-known manner, to close at 66 before breaking at I54 or recourse may be had to the speed'of operation to eliminate the necessity for this. In the event that it is desired to permit the starting arcs to flow in the lamps for a short interval, to heat up the tubes to insure operation at the lower normal temperature, the relay may be made of the slow acting type, by any of the well-known expedients, such a the placing of a large copper slug 68 on the core thereof.

In Figure 3 is shown a system for obtaining a change in turns-ratio between the primary and secondary windings wherein the source of power 28 is arranged to be connected always to the whole primary winding between terminal I00 and IOI. An auto transformer is again shown.

The secondary of this transformer is represented by the whole winding between IOI and H32. The secondary is tapped at I03 to produce a section IOI, I03 for supplying the normal operating potential to the lamps. This is indicated .as having fewer turns than the primary for use with lamps requiring less operating potential than that provided from the source.

The two lamps and their reactors are connected exactly as in Figure 1 and it remains only to describe how either the whole secondary or a portion of the same is used for energizing them. The lead I04 from the center of the reactors is connected to the bi-metallic element I05, of an evacuated switch I06, which carries the contact I01 normally in engagement with contact I08 connected by wire I 09 to the end of the secondary at I02 through the interposed resistor III Under these conditions a high secondary to primary turns-ratio exists and a striking potential is provided between points l0l and I02 of the transformer for starting the lamps. Within the envelope I06 is glow terminal II2 connected to an intermediate position H3 on the secondary of the transformer. This electrode, being at a different potential than any of the other electrodes in the switch envelope, which may be suitably filled with a quantity of ionizable gas and provided with an emissive material causes a glow discharge to be set up, the heat from which causes the bi-metallic supporting arm I05 of contact I01 to move toward the right and eventually engage contact II5 subsequent to which it dis' engages contact I08 in the same manner as described in connection with Figure 1. When this operation is completed only that portion of the secondary between IOI and I03 is applied to the lamps for operating them. There still remains within the switch a difference of potential between the glow electrode and the others which maintains the glow to hold the bi-metallic element stressed toward the right during all of the operation of the lamps. When the main circuit is opened to extinguish the lamps the glow is extinguished and the contact I01 returned to the position illustrated in the drawing ready for a restarting of the lamps.

In Figure 4 is illustrated a circuit in which a transformer having a primary separate from the secondary is used. This circuit also leads to the elimination of the reactors for the lamps, their function being performed by the separate secondaries one for each lamp in a manner which will be later described. Referring now to this drawing it will be seen that the separate primary winding comprises a number of turns between terminals 200 and MI, there being an intermediate tap at 202. The source of power 20 is arranged to be connected by suitable switching contacts 204 to either the whole primary or that portion of the same between 200 and 202. When in the second position the resistor 205 is interposed in the circuit.

Two identical secondaries, where identical lamps are used, are represented at 20? and 2 08, the first being connected through a condenser 209 to lamp 2I0 and the second being directly connected to lamp 2| I. The two lamps are connected together at 2I2 and through the small winding 2I3 back to the connected ends of the secondaries. The winding 2I3 represents diagrammatically the magnet for operating the contacts 204 in the same manner as the magnet 60 in Figure 2. I

It will be seen that when the arrangement'of of the three lamps.

'contacts is such that the source of power is con- :nected between 200 and 202 a high secondary to primary turns-ratio exists and striking voltages are provided in each secondary, wherea when the whole primary is energized a lower or operating voltage is provided for-each of the lamps.

In order to prevent excessive current flow to each of the negative resistance lamps, suitable magnetic shunts are arranged in the common core ofthe transformer to provide a high leakage flux which produces a-counter-E. M. F. in the primary winding and hence reduces the current flow and the output of the transformer. This leakage reactance may be achieved through the use of a core section somewhat as illustrated in Figure '7.

Here the core includes three connected legs 215, 216, and 211, the center one of which is provided with the primary winding and the outer ones with the secondary windings respectively. The connecting portions of the core structure at the top and bottomare designated-2 I 8 and 2 I8 respectively, The magnetic shunts are shown at 220 and 22! and may be provided with air gaps as at 222 if desired. These same shunts are diagrammatically represented in Figure 4 at 220 and 221 as existing between the sections of the coils on the common core.

The resistor 205 shown in Figure 4 serves the same purpose as theresistor -42 in Figure 3, that of limiting the current when only a portion of the primary is in operation. The circuit of Figure 4 uses a minimum of critical materials since no separate reactors are required and no additional metal is needed in the transformer above the absolute minimum used for normal operating.

The circuit of Figure 5 is not substantially different from that of Figure 2 except that the primary 300, which is tapped to change the turnsratio in the manner described in connection with Figure 4, is entirely separate from the secondary 301 instead of being arranged as an auto transformer as shown in Figure 2. The operating coil 303 for the relay is shown connected between one end of the secondary and the intermediate tap on the reactors 304.

The circuit of Figure 6 is similar to that of Figure 5 buthere the singlesecondary 400 is connected to oneend of each of three reactors 40!, 402, and 403. These may be on a common core, as shown and constructed in accordance with the previously mentioned application or they may each be independent. The-opposite end of the secondary is,-through wire 404, connected to one end of each of the three lamps 405, 406, 401. The .opposite ends of each of the reactors are connected to the remaining ends respectively of the several lamps. The circuit of at least one of the lamps is provided with the power-factor changing condenser 408. The relay operating coil M0 is so interposed in the secondary circuit that current to all three lamps must flow through it. In this manner, by properly designing this coil, the circuit may be arranged so that there is no transfer of the'source of potential from the partial to .the whole primary until an arc has struck in each This prevents premature operation which might leave one or two lamps unilluminated. It will be noted that this characteristicalso applies to the arrangements of some of the other figures and is largely controlled by the use ofso-called marginal relays which do not close unless the current flow through them exceeds a predetermined minimum.

Fluorescent lamps which are especially de- --signedfor cold cathode starting do not have filament electrodes intended to be heated for starting, an'dit 'hasbeen found particularly desirable, especially for outdoor operation, to use high current densities for their starting since this vaporizes the mercury more readily and heats up the .gas within the tube quickly. Such lamps, however, are not readily available on the market and recourse is usually had to the so-called filament electrode type of lamp intended for hot cathode starting by heating the two filaments to incandescence. These filaments are coated with an electron emissive material and are readily damaged by excess operating temperatures so that care must be exercised, in starting by the cold cathode method, to limit the current densities to those which are safe and will provide normal or extra life for the filaments. Unfortunately the current limiting devices, such as reactors or the like, used to hold down the normal operating current to a safe value are of insufiicient impedance to limit the starting current at the much higher starting voltages.

In the embodiment of the invention illustrated in Figure 8 a circuit arrangement is shown which provides additional impedanceto the current-only during the starting operation and switching mechanism is arranged not only for inserting and removing this impedance but for making the change-over from the starting to the operating voltage and vice versa in a manner somewhat similar to those already described.

Referring now to the figure, it will be seen that it makes use of an autotransformer 500 although obviously separate windings might be used in the manner illustrated in Figures 4 and 5. This transformer contains a two-section primary, that bearing the reference character 50! being used for starting purposes, and this portion plus the section 502 being .used for operating purposes whereby, under the latter-condition, the ratio of turns to that of the secondary winding 503 is lower.

A source of alternatingcurrent 580 and a main switch 505 are connected to the end 5136 of the winding on the transformerand, through an aumatic switch including contacts 581 and 598 which are always closed when the switch 585 is open, this source ofcurrent is also connected to the terminal 501 of the starting section of the primary. The terminal 566 of the transformer is connected by conductor 509 to the left-hand ends of the lamps'5I 0 and M2, the current passing by way of conductors 514 through a relay coil 5L5. The secondary terminal M8 is connected by a wire5i9 to the junction 5280f a pair of starting resistances 52L whose opposite ends are respectively connected to the two ends of the balanced reactor coils 522 and 524, exactly like those shown in Figure 1. The remaining terminals of the reactor coils 52-2 and .524 are connected to the opposite ends ofthelamps bid-and 512, a condenser'525 being interposed in enact the circuits to improve the power factor-and eliminate .stroboscopic effects.

Under the conditions illustrated and just described, the closing of switch 505 energizes primary section 50l of the transformer anda high potential is induced between the terminals 555 and 513 of the transformer which is applied to the opposite ends of the lamps through the current limitingreactors -52'2 and 524 each inseries with one of the resistors 52!. The reactors 522 and 524 aredesigned to-hold down the operating 9 the starting current to the desired low figure when the voltage is much higher. They are therefore augmented by the'simple resistors 52! in series therewith for this purpose. For operating the lamps, however, it is desired to increase the number of turns in the primary so that its ratio to the secondary shall be lower, whereby the overall induced voltage applied to the lamps will be sufiiciently low for continuous operating purposes, when the reactors alone are adequate to limit the current. The switching operation to transfer from starting to operating conditions must therefore include means to remove the resistors 52! from the'lamp circuits.

A composite relay shown in the dotted line box 530 takes care of all the switching. It is actuated by the coil !5 which is adequately energized only when the arcs strike in the two lamps, since it is inserted in the main conductor 509 leading thereto. When this coil is energized, it pulls down its core attached to the insulating frame 53! which closes the spring mounted contacts 532 and 533, the former being connected by wire 534 to terminal 535 at the end of the operating primary comprising the sections 50! and 502. Lower contact 533 is mounted on the same spring as the lower contact 508 on the switch which closes the starting section of the primary. When the spring carrying contact 532 moves downwardly, a circuit is closed at 532, 533, and one is opened at 50'! and 508, thereby applying the source of alternating current across the two primary sections 50! and 502 in series, and disconnecting it from the single section 50!. This provides proper operating voltage from the whole winding of the transformer.

A three-contact switch is also operated by the frame 53! on its downwardly movement and serves to shunt the two resistors 52! for which purpose the middle connection 52!] thereof is connected to the spring carried contact 537, while the opposite ends of the two resistors are connected respectively to spring mounted contacts .538 and 539. When the frame 53! is drawn down wardly by the relay winding 5l5, the three contacts 531, 538, and 539 are drawn together, shunting out the resistors and connecting the inner ends of the reactor windings directly to terminal 5l8 of the secondary. Operation is now exactly as illustrated in connection with Figure 1 or 2.

. For starting a hot cathode type of lamp by the cold cathode method, it has been observed that the best results are obtained if this is achieved in three steps: first, the striking of an arc of just sufiicient intensity so that it will locate itself at some point on the filament of the electrode which is coated with emissive material; second, the regulation of the arc current to just a sufficient intensity to bring the striking point on the filament to an electron emissive temperature in a predetermined time; and third, the transfer from starting voltage to operating voltage only after the filaments have attained this emissive temperature. The circuit just described in connection with Figure 8 permits obtaining these desired results since the intensity of arc current can be regulated by changing the size of the resistors 52!. The time elapsed between closing the starting circuit and transferring to the operating circuit can be regulated by means of the relay 530 which may be of the time delay type. The time delay may be obtained by any well known means, such as the use of a thermal relay, a dash pot, a mercury pocket, or the well known use of a heavy metal slug such as shown at 540associated with the core or winding of the relay. It will be appreciated of course that there is no current flow in the relay winding until the striking of the arcs in the lamps, although the starting current may have been applied for several seconds. The time delay interval will therefore occur between the instant of striking of the starting arcs or are and the time of transfer from the starting to the operating condition. This period can be regulated, in the initial design of the relay, or can be made variable to take care of different types of lamps. If a cold cathode type of lamp is used, no time delay is necessary and the transfer can take place immediately upon the striking of the starting arc.

The above described circuit arrangement is of importance, for the contacts are so disposed in the circuit that only one pair of them opens under load. The contacts 50! and 50B are separated while carrying current. The others are only closed under what might be termed load conditions, but since contacts 532 and 533 practically shunt 50'! and 508 while they are being opened, there is not much chance for these latter contacts to burn. The remaining contacts do not open until the main switch 505 has been opened and all current has stopped flowing. They can therefore be relatively small, not only because they do not open under load but because they carry relatively low currents and for only brief intervals during the starting operation. A simple and compact relay of the telephone type can therefore be used which is good for millions of cycles of operation. I

As an example of the values of voltage, current, resistance, and the like, the following may be noted as an optimum arrangement for controlling two 40-watt fluorescent lamps as arranged in the circuit of Figure 8:

Operating alternating current sourcevolts Operating voltage across the lamps200 Striking voltage across the lamps400 Resistance of resistors 52!1200 ohms each Capacity of resistors 52!-20 watts each Striking current-.2 ampere for each lamp Operating current-.4 ampere for each lamp Current in relay coil 5!5.4 ampere Resistance of coil 5l5-8 ohms Operating loss in relay3.2 watts Time delay in relay- 2.5 seconds The arrangements of circuits and apparatus as shown are suitable for the operation of any desired negative loads and cannot be the cause of any uncontrollable potential or current disturbances. Under ordinary circumstances starting voltages are needed only for short periods, say for considerably less than one second to a maximum of 30 seconds. Such voltages are not dangerous in equipment designed for normal operation at lower voltages because of the short time interval precluding any undue heating in the copper or iron.

Having thus described the invention, what is claimed as new and desired to be secured by Let- .ters Patent is:

v 1. In a circuit for starting and operating fluorescent lamps, the combination with a source of alternating current and a lamp adapted for cold cathode starting, of a transformer having a primary winding and a secondary winding, circuit means connecting'the secondary winding with the lamp, circuit means connecting the primary winding with the source of potential and means under control of the current delivered to the 11 lamp to change the turns-ratio, or primary to secondary to provide first a'high starting voltage for striking an arc in the lamp and then a lower operating voltage.

2. In a circuit for starting and operating fluorescent lamps, the combination with a source. of alternating current and a lamp adapted for cold cathode starting, of a transformer having a secondary winding, circuit means connecting the secondary winding with said, lamp to supply current for the same, aprimary winding having the correct turns-ratio andcurrent carrying capacity for optimum operationof the secondary for normal burning of the lamp, means'temporarily to connect said source to. less than the full number oi turns of the primary to in'duoea high startin voltage in the secondary and means automatically to connect the whole primary to said source to induce the desired operating voltage in said secondary upon the flow of starting current in the lamp.

3. In a circuitfor. starting and operating fluorescent lamps, the combination with a source of alternating ourrentand a lamp adapted for cold cathode startingof a transformer havin a primary winding and a secondary winding, circuit means connecting the primarywinding directly with the said source, circuit means connecting the full secondary winding with the lamp when the primary is die-energized and automatically time lag switching means to transfer the lamp to a portion of the secondary sufficient to provide proper operating voltage therefor, said time lag means being responsive to voltage in the. transformerwindings,

4. In a circuit for cold cathode starting and normal operation of aplurality of fluorescent lamps, the combination with a source or alternating current at a commercial potential, and a plurality of lamps, of, a transformer having a secondary windingf'or and; connected to each lamp and a, single primary winding, the primary winding having a suitable turns-ratio to each secondary to supply the-connected lamp with the proper operating potential, said primary having a tap connected with a, lesser number of turns having such a ratio tcthe secondaries as. to sup.- ply high starting potential to the associated lamps, a relay biased to connect the tapped portion of the primary with the source of current and a magnet coil connected to be energized by current flow to one of, said lamps to operate the relay to connect the source to the whole of said primary.

5, In a circuit for cold cathode starting and normal operation of a plurality of fluorescent lamps, the combination with a source of alterhating current at a commercial potential, and a plurality of lamps, of a transformer having a secondary winding for and connected to each lamp anda single primary winding, the primary winding having. a suitable turnseratio to each secondary to supply the connected lamp with the proper operating potential, said primaryhaving a, tap connected with a lessernumber of turns havin such a ratio to the secondaries as to supply high starting. potential to theassociated lamps, a relay biased to connecttheitapped portion of the primaryv with, the'source of current and a. magnet coil nn cted. to'bei nersi d b ur nt flow tqall of,sai d lampsto operate the relay to connect thesour'ce to the whole of said primary, said coil having such characteristics that it does not overcome the bias until starting current is flowing tolall ofthe lamps.

6. In a circuit for cold cathode starting and q 'r t n f a luor cent lama he om;- I

bination with a, sourceof. alternating current at a. commercial potential and a lamp, of a trans,- former having a secondary winding, connected to the lamp and a primary of suitable turns-ratio to provide the correct operating voltage for the lamp, a core for said transformer, an intermediate tap on said primary, aswitch to alternatively apply the source to thetapped portion of or the whole primary forv respectively starting and operating the lamp, the primary winding wire size and the core volumebeit g lust'large enough to handle the normal operating load and hence temporarily overloaded when the tapped portion of the primary is connectedtg the source.

'7. In a circuit for cold cathode starting and normal operation of a fluorescent lamp, the combination with a source of alternating current at a commercial potential and a lamp, of a trans former having a secondary winding connected to the lamp and a primary of suitable turns-ratio to provide the correct operating voltage for the lamp, an intermediate tap on said primary, 2. switch biased to connect the tapped portion of the primary to said source and movable to connect the whole of the primary to said source, said switch being arranged to complete the second mentioned connection before the first is broken, and means in the primary circuit to limit the current flow therein during the circuit changing operations of the switch.

8. In a circuit for cold cathode starting and normal operation of a fluorescent lamp, the combination with a source of alternating current at a commercial potential and a lamp, of a transformer having a secondary winding connected to the lamp and a primary of suitable turns-ratio to provide the correct operating voltage for the lamp, an intermediate tap on said primary, a switch biased to connect the tapped portion of the primary to said source and movable to connect the whole of the primary to said source, said switch being arranged to complete the second mentioned connection before the first is broken, and means in the primary circuit to limit short circuit current in any portion thereof during the circuit changing operations of the switch, said last mentioned means being so connected as to limit the current flow to the primary during only the biased positioning of the switch.

9. In a circuit for cold cathode starting and normal operation of a fluorescent lamp, the combination with a source of alternating current at a commercial potential and a lamp, of a transformer having a secondary winding connected to the lamp and aprimary of suitable turns-ratio to provide the correct operating voltage for the lamp, an intermediate tap on said primary, a switch biased to connect the tapped portion of the primary to said source and movable to connect thewhole of the primary to saidsource, said switch being arranged to complete the second mentioned connection before the first is broken, and means having a time delay action for controlling the movement of said switch from biased to whole primary position.

10. In a circuit for starting and operating flu- .orescent lamps, the combinationwith a source of alternating current and a lamp adapted for cold cathode starting, of a transformer having a pri mary winding and a secondary winding,'circuit means connecting the secondary winding with the lamp, circuit means connecting the primary winding withthe source of potential; means to change the turns-ratio of primary to secondary to provide either high starting voltage or low operating voltage, an impedance normally inserted between the lamp and secondary to limit the starting current, and means automatically to eliminate said impedance when operating voltage is applied to said lamp.

11. In a circuit for cold cathode starting and normal operation of a fluorescent lamp, the combination with a source of alternatin current at a commercial potential and a lamp, of a transformer having a secondary winding connected to the lamp and a primary of suitable turns-ratio to provide the correct operating voltage for the lamp, a core for said transformer, an intermediate tap on said primary, a switch to alternatively apply the source to the tapped portion of or the whole primary for respectively starting and operating the lamp, a reactor in the circuit between the lamp and secondary to limit the operating current to a predetermined value but being of insuflicient reactance'to limit the starting current to the desired amount when the higher starting voltage is applied resulting from applying the current source to the primary tap, a resistor connected to augment said reactor during starting, and means on said switch to remove the resistance from the circuit when the source of current is applied to the whole primary winding.

12. In a circuit for starting and operating fluorescent lamps, the combination with a source of alternating current, a main switch, and a lamp of the filamentary cathode type, having shunting means on the filaments, of a transformer having a secondary winding, a reactor, said lamp, secondary and reactor being connected in series for normal lamp operation to provide the requisite operating current and voltage, a primary winding on said transformer having the correct turns-ratio for excitation of the secondary for normal lamp operation, switching means to connect said source to less than the full number of turns of the primary to temporarily induce a high starting voltage in the secondary when the main switch is closed, a supplementary impedance, said switching means bein arranged to connect said impedance in the secondary circuit to limit the lamp current to that necessary for starting at the increased voltage, and a relay coil for actuating said switching means, said coil being responsive to starting and operating current to change and maintain the switching means from star-tingto operating condition.

13. In a circuit for starting and operating fluorescent lamps, the combination with a source of alternating lamps, a main switch, and a lamp of the filamentary cathode type, having shunting means on the filaments, of a transformer having a secondary winding, a reactor, said lamp, secondary and reactor being connected in series for normal lamp operation to provide the requisite operating current and voltage, a primary winding on said transformer having the correct turnsratio for excitation of the secondary for normal lamp operation, switching means to connect said source to less than the full number of turns of the primary to temporarily induce a high starting voltage in the secondary When the main switch is closed, a supplementary impedance, said switching means being arranged to connect said impedance in the secondary circuit to limit the lamp current to that necessary for starting at the increased voltage, a relay coil for actuating said switching means, said coil bein responsive to starting and operating current to change and maintain the switching means from starting to operating condition, and means to delay the operation of said switching means for a predetermined period after the beginning of starting current flow.

RUSSELL WILLIAM KEISER. CHARLES PHILIPPE BOUCHER.

REFERENCES CITED The following references are of record in the

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