US2733382A - campbell - Google Patents

Description

Jan. 31, 1956 J. H. CAMPBELL PULSE STARTING SYSTEM FOR FLUORESCENT LAMPS Filed March 14, 1950 2 Sheets-Sheet l HAD/650827? Lamp Fig 1.

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Jan. 31, 1956 J. H. CAMPBELL 2,733,382

PULSE STARTING SYSTEM FOR FLUORESCENT LAMPS Filed March 14, 1950 2 Sheets-Sheet 2 Fig 4.

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United States Patent 2,733,382 PULSE STARTING SYSTEM FOR FLUORESCENT LAMPS John H. Campbell, Painesville, Ohio, assignor to General Electric Company, a corporation of New York Application March 14, 1950, Serial No. 149,535 2 Claims. (Cl. 315-97) a for the sole purpose of starting the are or discharge within the lamp, and this equipment is completely inopera tive during normal lamp operation. In many installations not only is the starting equipment not gainfully utilized during operation, but it actually causes awastage 1 of electrical energy.

Accordingly, it is an object of my invention to provide a new and improved system of starting and operating fluorescent lamps which possesses inherent features of economy by providing onlyone starting device for a number of lamps in multiple.

A further object of my invention is to provide a new and improved system of starting andoperating fluorescent lamps which eliminates the need for high voltage transformers when used with instant start lamps.

Still a further object of my invention is to provide such a system which eliminates the need for thermal or glow switches when operated with preheat of the electrodes in a fluorescent lamp. p

A feature of my invention, a s applied to an installation of fluorescent lamps in multiple, is the provision of a central source for generating high intensity pulses of short time duration, which are either substituted for the line voltage or superimposed thereon for a brief interval at starting only; During normal operation, the central source of pulsed voltage is effectively disconnected from the line. Y a 1 g i i For further objects and advantages and for a better understanding of my invention, attention is now directed to the following description and accompanying drawings. The features of my invention believed to. be novel will be more particularly pointed out .the appende d claims.

Referring to the drawings:

Fig. 1 is a block diagram illustratingin generalized form a pulse starting and operating system for fluorescent lamps in accordance with my invention.

Fig 2 is a schematic diagram of a preferred embodiment of my invention illustrating a pulse starting system for'fluorescent lamps operated in pairs with the wellknown lag-head two-lamp circuit.

Fig. 3 shows a pair of curves-illustrating the waveform of the line voltage and of the-pulse voltage generated in the preferred embodiment of Fig. 2.

Fig. 4 is a schematic diagram illustrating another embodiment of my invention which is particularly adapted to the operation of low wattage fluor'escent,lamps.of the preheat type in multiple.

Fig. 5 illustrates another embodiment of my invention which is particularly-adapted to the operation of fluorescent lamps from a direct current supply. 7 p h Referring to Fig. 1, the block: diagram therein illustrates the general application of my pulse starting system to a number of fluorescent lamps in parallel. The various components of the blocks will be described in detail with reference to the succeeding figures. In general, my invention finds its most advantageous application where a number of fluorescent lamps, as represented by blocks 1, 2, and 3, are to be operated in parallel from a common supply line 4, 5, and are to be controlled from a central point. Then, instead of providing starting equipment for each fluorescent lamp operating circuit, I provide a single source of voltage pulses at the central switching point, said source being represented by block 6. The pulse source may either substitute a series of short high voltage pulses for the regular supply voltage during a brief period immediately after a manual control switch is first turned on; or, again, it may superimpose high voltage pulses on the regular line voltage waveform. The former is preferably used with fluorescent lamps of the instant start type, and the latter with fluorescent lamps requiring preheat of the cathodes. With instant start lamps, the pulse energy must be high enough to cause a hot spot to form on the cathodes of all the lamps, but

not so high as to cause any one of the lamps to strike its normal arc discharge because such lamp 'would then absorb all the energy transmitted from the pulse source and prevent the other lamps in multiple from starting. With fluorescent lamps of the type requiring preheat of the cathodes, the pulse energy provided need be just suflicient to 'ionize the gas in the lamps without striking the arc discharge.

Referring to Fig. 2, I have illustrated therein a pre ferred embodiment of a pulse source operated in conjunction with a lag-lead two-lamp circuit and I have enclosed the constituent elements within blocks in dotted outline, these blocks being denoted by like reference numerals as in Fig. l. The pulse source comprises a saturable choke coil or inductor 7, the primary winding 8 of a transformer 9, and a capacitor 11 connected in series with a switch 12 across the supply 4, 5. Transformer 9 is provided with a secondary winding 10, one side of which is connected directly to the utilization line 4' and the other side of which may be connected to the utilization line 5' through switch 12. The supply line 4 may be connected to the utilization line 4 by means of a switch 12', Whereas the supply line 5 continues directly into the utilization line 5.

The utilization lines 4, 5, lead directly to the two input terminals of the operating circuit of a pair of fluorescent lamps 13, 14 of the low pressure positive column type. The particular operating circuit illustrated consists of a step-up autotransformer 15 comprising a portion 16 across which the utilization lines 4, 5 are connected, the junctures with these lines being in effect the input terminals. The high voltage side of. autotransformer 15 is connected through an inductor 17 to lamp 13 and through an inductor 18 in series with a capacitor 19 to lamp 14. In accordance with well-known principles, inductor 17 causes lamp 13 to operate with a la ging power factor, whereas the combination of inductor 18 and capacitor 19 causes lamp 14 to operate with a leading power factor. The operating circuit for lamps 13 and 14 may be of the type commonly utilized for the switch starting of 40 watt lamps, and which is commonly known in the fluorescent lamp industry as a lag-lead two-lamp switch-start ballast. In the present instance, I utilize the circuit without the switch starting connections, and I preferably provide lamps 13 and 14 with cathodes capable of withstanding instant starting. For instance, lamps 13 and 14 may be 40-watt instant start fluorescent lamps which are provided with cathodes containing large amounts of emissive material. It might be mentioned at this point that conventional operation of instant start .ratiopf approximately 2 1 to v1,; :15, c ul no s a l mps 13. a

lamps iugaccolidancewithxthe prior art, requires a transqu pme ccnt iaed'iapulse source .6 whose operation will now be described.

To put lamps '13 and-14mm operation and, likewise, other lamps which may be, connected in similar fashion as represented symbolically byblocks ,2 and 3, switch i2. is initially closed for a fewseconds, the exact length of time depending on various factors which will be considered hereafter, and switch 12' is then closed simultaneously Withthe reopening ofswitch 1'2. xlt need hardly be mentioned that switches 12 and .12 may be mechanically interlocked by means of a delayed escape mechanism suchthatthe operationnf. av singlelever will perform, the three operations just.mentionedinltheir proper sequence. Since such switchinginechanisms are well known and available onthe market, none has been illustrated in the drawings.

When switch 512 is initially closed, the current flows through the branch circuit comprising reactor '7, primary winding 8 and capacitor 11 in series. These elements are sodesigned that the .magnetic core of reactor 7 saturates due to the currentthrough the circuit. As a result, the voltage induced in secondary winding is characterized by a high intensity peak of short time duration. Referring to Fig. 3, curve therein illustrates the sinusoidal waveform of the supply voltagereceived from the line conductors 4, S and curve 21 illustrates the sharply peaked waveform of the pulses impressed on the utilization circuit 1', 5'. It will be observed that the pulse voltage impressed on the utilization circuit, whereas it attains a high peak, actually contains less energy than the sinusoidal line voltage due-to'the short time duration ofthe pulses. Transformer 9 has a stepup ratio providing a peak voltage having a maximum amplitude approximately twice the amplitude of the line voltage.

The pulses are impressed through the utilization circuit 4', 5 on the autotransformer 15 of the lamp operating circuit contained in block 1, and similarly on the autotransformers contained in the other blocks'2 and- 3. Autotransforrner 15 causesthe pulse voltage applied to it to be increased or stepped up substantially in accordance with its turn ratio. Thus, since transformer 9 provides a peak voltage of twice the amplitude of the supply voltage, and since autotransforrner 15 provides its usual r 2 to' l voltage step up, the peak voltage applied to lamps 13 and 14 is approximately four times the line voltage. The energy content of the pulses, which energy content is dependent upon their duration, is sufiicient to cause the lamps to form a hot spot on their cathodes but is not sufficient to cause the normal arc discharge to occur within the lamps due to the spacing of consecutive pulses. It is important that this requirement be met, because I have found that if the energy content of the pulse waveform is too high, one of the lamps will arc and will absorb the energy which would otherwise have gone to produce hot spotsin the remaining lamps, so" that these will not start.

With regard to the requirement that all the lampsform a hot spot and that none attain a normal arc discharge, I have found that this may be achieved successfully by providing pulses of suitably short time duration with respect to their spacing or repetition interval. It is a well-known fact that an arc discharge through a gashas a negative resistance characteristic. However, if sharp pulses of voltage at comparatively longtime intervals apart are utilized, rather than a rmidirectional voltage or a sinusoidal alternating voltage, the degree of ionization of the gas cannot increase at the same rate as the steep waveform of the pulse; and, as a result, the discharge exhibits a positive resistancecharacteristic, that is, o ne in which thevoltage ..ceniiasln.taiasurath 4 drop increases rather than decreases with current. Ac-

eata ltaglama tqrma. 1. .01 snot, provide the pulses with a short time duration with respect to their spacing or repetition interval; and, to take care of a greater number of lamps, 1 preferably increase this peak pulse amplitude, rather than their time duration.

The pulse circuit may readily be designed such that all the lamps in the operating circuits form hot spots on their.-cathodes.-wi1hiniatfewssecondseafter the initial closing of switch 12. Thereaften the closing of switch 12' applies the normalsinusoidal-line voltagedirectly across autotransformer 15 and co this .voltage has a suf- V ficient energy content to support an arc discharge in all the lamps, mediately.

Referring to Fig. 4, I have illustrated therein another embodiment of my invention which is particularly adapted to the starting of fluorescent lamps whose cathodes requirepreheatat startingin o ider toinsure'reasonable life. The pulsing.circuit-contained;withinblock 6 is quite similarto that-illustrated.inJEig. 2 with this variation that the secondary windinglil-oftransformer 9'is arranged to be placed in series between the supply linedand the utilization lined. Switch l2, in this particular embodiment, is arranged to .short circuitrsecondary winding 10 and normal operation ensues practically 1m providea. direct. connection between lines 4 and 4 when closed.

The operating circuit contained in block 1 comprises a fluorescent; lamp fiilofzthe type'having apair of thermionic electrodes 31. and '32 which normally require the application of heating current in order toraise them to an electron emitting temperature and prevent destructive sputtering of activatedelectronemissive material at starting. Lamp 3915 connected in series with a current limiting reactor '33 across the utilization lines 4', 5'. This circuit comprises, in addition, an electrode heating transformer 34- -of which the-primary'winding 35 is connected in parallel with "lamp 3'0, and of which the secondary windings -36-and 3-7 are connectedacross thermionic electrodes 31 and 32,-res pectively.

The operation of the switches in the embodiment of Fig. 4 is similarto that described with reference to Fig. 2, the only difference being that the pulse voltage is added to the sinusoidal voltage provided by the supply. Thus, the utilization lines '4", 5' receive a composite voltage containing both the normal supply voltage and the pulse voltage. The pulses cause the gaseous column within lamp 3!) to ionize. In addition, the supply voltage operates in normal manner on transformer 34 whose secondary current heats electrodes 31 and 32. When the electrodes have attained their electron emitting temperature, since the gaseous column has already been ionized by the pulses, the arc strikes without difficulty. One of the advantages of supplying pulses in this circuit is that the lamps ionize due to the high-intensity peaks of the pulses and thereafter cannot, fail to start on the normal line voltage. Thus, there is no necessity for thermal or glow switches to provide, an inductive surge to initiate ionization within the-lamps. v

Referring toiFi'g. 5, the pulsing circuit 6 therein illustratedis'designedffor pulse star'tinglamps from a direct current supply, in accordance with my invention. The pulse generator proper comprises a tapped inductor 40 connected, in series with a discharge tube 41 and switch 12, across theuni directionalsupply 4, S, the tapped portion of theinductor being shunted by a capacitor 42. Inductances 43 and 44and shunt capacitor 45 constitute a T-filter, which is provided in order to prevent pulse energy from feeding back to the direct current supply. The lamp' operating circuit comprises lamps 13 and 14 connected-in serie's'with resistiveballasts 46 and 47 across the utilization lines 4 5'. Ballasts 46 and 47 may be the usual tungsten filament lamp.

'In operation when switch "ll initially closed, a series ofdischarges occuracross the electrodes of tube 11 which produce trains of damped oscillations in capacitor 42 and inductor 40. The T-filter forces these trains of oscillations to travel through the utilization lines 4', 5' to the lamp operating circuitswhereupon hot spots are formed on the lamp electrodes. After the arcs have struck Within the lamps, switch 11 is opened and the generation of pulses ceases, the lamps thereafter operating in normal fashion with ballasting provided by the tungsten lamps 46 and 47.

While my invention is applicable to the operation of a single lamp, it naturally finds its most advantageous applications in combination with a number of lamp circuits connected in multiple. Thus, it is ideal for the operation of large numbers of lamps in buildings or halls wherein it is desirable to have a single control switch for all the lamps. It will be evident to those skilled in the art that it is economically advantageous to provide a single pulsing source and thereafter provide transformers having low step-up ratios, such as step-up ratios of 2 to 1, for each individual lamp, than to provide at each individual lamp a transformer having a high step-up ratio, for instance 4 to 1, as would be required in the absence of a pulse circuit. My invention provides economic advantages not only from the point of view of first installation cost, but also from the point of View of electrical consumption, as the operating losses in transformers having an open to operating voltage ratio of 2 to 1 may always be made lower, other factors being equal, than in transformers having a ratio of 4 to 1.

Although certain specific embodiments have been shown and described, it will, of course, be understood that various modifications maybe made without departing from the invention. Thus, the particular pulsing circuits which I have illustrated may be replaced by other circuits known to the art which perform similarly. Likewise, the lamp op erating circuits which I have illustrated are intended as nonlimitative examples, and it will be apparent that various other ballasting circuits commonly utilized with fluorescent lamps may be substituted therefor. The appended claims are, acccordingly, intended to cover any such modifications coming within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A starting and operating system for fluorescent lamps of the thermionic cathode positive column type, comprising a plurality of said lamps, an alternating voltage supply, operating circuits for said lamps each comprising a pair of input terminals and connected in parallel across said supply, each of said operating circuits comprising a high leakage reactance transforming means havprovide regulation after starting, and a pulsing circuit connected between said operating circuits and said supply,

said pulsing circuit comprising a satnrabie reactor, the primary winding of a transformer and a capacitor serially connected through a first sv-si'tch across said supply, and a secondary winding of said transformer with a second switch and connections for temporarily substituting said secondary winding for said alternating supply to energize saidoperating circuits, said saturable reactor and said capacitor being proportioned to produce pulses of short time duration and high intensity in said secondary winding when said first switch is closed, said pulses having a time duration short enough to cause said lamps to exhibit a positive resistance characteristic thereto.

2. A starting and operating system for fluorescent lamps of the positive column type having filamentary thermionic cathodes, comprising a plurality of said lamps,

an alternating voltage supply, operating circuits for said lamps each comprising a pair of input terminals and connected in parallel across said supply, each of said operating circuits comprising reactive transforming means having a normal open circuit to operating voltage ratio less than that required to start said lamps but sufficient to provide regulation after starting and including means for supplying preheating current to said electrodes, and a pulsing circuit connected between said operating circuits and said supply, said pulsing circuit comprising a saturable reactor, the primary winding of a transformer and a capacitor serially connected through a first switch across said supply, and a secondary winding of said transformer with a second switch and connections for temporarily substituting said secondary winding for said alternating supply to energize said operating circuits, said saturable reactor and said capacitor being proportioned to produce pulses of short time duration and high intensity in said secondary winding when said first switch is closed, said pulses having a time duration short enough to cause said lamps to exhibit a positive resistance characteristic thereto.

References Cited in the file of this patent UNITED STATES PATENTS Waguet Feb. 19, 1952

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