US2680211A - Sequence pulse starting circuit for fluorescent lamps - Google Patents

Description

June 1, 1954 J. CAMPBELL 68 SEQUENCE PULSE STARTING CIRCUIT FOR FLUORESCENT LAMPS Filed March 14, 1950 Fig 1. L

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Patented June 1, 1954 UNITED STATES PATENT OFFICE SEQUENCE PULSE STARTING CIRCUIT FOR. FLUORESCENT LAMPS John H. Campbell, Painesville, Ohio, assignor to General Electric Company, a corporation of New York Application March 14, 1950, Serial No. 149,536 3 Claims. (Cl. 3.1596) l 2 This invention relates generally to the starting In the drawing: and control of electric discharge devices, such as Fig. 1 is a schematic diagram or a starting-cirlow pressure positive column lamps of the fluocuit embodying my invention and illustrating rescent type, and more particularly to circuits the operation of two fluorescent lamps in series suitable for use with fluorescent lamps-which refrom a direct or alternating curent source.

quire preheat of their thermionic cathodes at ig- 2 is a schematicd of o her 01 starting. cuit embodying my invention, modified to permit My invention is concerned with the series opthe use of thermal type switches rather than the eration of fluorescent lamps from a voltage source, glow type illustrated in Fig. l.

of which the terminal voltag is insufficient to Referring to Fig. 1, the circuit therein comstart a discharge by means of the usual inductive prises a pair of fluorescent lamps I, l electrically surge switch-start circuit, and is applicable to connected in series with each other and with a both alternating and direct current circuits. ballast resistance 2 across a pair of input termi- It is an object of my invention to provide a new nals 3, 3 adapted to receive either alternating'or and improved starting and operating arrangedirect current. The devices I, I are positive colment for fluorescent lamps provided with at least umn discharge lamps compri n es en ially an one thermionic electrode, which arrangement evacuated glass envelope containing a mixture of employs a minimum of equipment and assures argon at a pressure of a few millimeters along reliable starting, together with efflcient operation. with a small quantity of mercury. The electrodes Another object of my invention is to provide 4, 5 and 4, 5' sealed into the ends of the lamp an improved starting arrangement for fluoresmay consist of coils of tungsten Wire coated With cent lamps which allows the sum of the voltage activated electron emitting materials such as drops across the lamps during operation to b a, barium and strontium oxides. If desired, each of high proportion of the line voltage, thereby in e devices y be a commercial W D suringahigh operating efiiciency. 5 sure fluorescent lamp wherein the envelopeis One of the features of my invention is the procoated internally with a suitable luminescent mavision, in the starting circuit, of transforming terialhe a la t si t 2 pr f a y as a means such asan ignition type pulse transformer, positive temperature coefiicient of resistance in of which a primary winding portion is connected order to provide good current regulatin charin series with the discharge circuit of a number acteristics and may, as illustrated, consist of an of fluorescent lamps. Asecondary winding-porincandescent tungsten fila nt amp.

tion of the pulse transformer is connected to, an ner f electrode 4 n p l i5 @011- auxiliary starting. electrode or capacitive plate nected, by means of a shunting circuit, to a ter associated with. each lamp. The filamentary minal of electrode 5. This shunting circuit comelectrodes in the lamps are in series with a reprises aresistance 6 and a switch 1 which maybe sistance and a switch device preferably of the of any suitable type, either manually or autoglow or of the thermal type, in order to allow prematically operable. For instance, I have illusheating of the electrodes at starting. Such cirtrated a glow type switch comprising a glass encuit connections may be extended to include any veiope 8 ta n an a as such as n number of lamps, depending upon the magnitude and including therein a pair of electrodes i? and of thesupply voltage. In starting, whenever one It, electrode l8 consisting of a curved bimetal of the switches opens, a pulse is generated-by the lie strip. In its normal position, electrode 11 pulse transformer which is applied to the .capacidoes not make contact with electrode It; howtive plates of all the'lamps, including th lamp ever, when a suiiicient voltage is applied across whose associated switch operated to produce the the glow tube, a discharge occurs therein which pulse. The lamp in question then starts and the heats up the electrodes and causes the curved other switches successively open until all the end of electrode l8to bend over and make con- .lamps have started, a pulse being generated at tact with electrode l7, whereupon the switch is the opening of any one switch to start its assoclosed and, a short-circuit being formed, the glow ciated lamp. ceases. After a brief interval of time, the elec- For further objects and advantages-and for a trodes cool whereupon they separat once more,

better understanding of my invention, attention and the circuit is opened. After lamp I starts, is now called to the following description and to the voltage drop across it is less than the ionizing the accompanying drawing. The features or my potential of thegas within the glow wi h. 'A invention believed to be novel willhe more-par- :cordingly, no glow occurs, the electrodes do not ticularlypointedout inthe appendedclaims, become heated, and the switch stays permanently opened. Lamp I is provided with a similar shunting circuit comprising a resistor 6' and a glow switch I.

In accordance with my invention, I provide a pulse transformer 9 which may be a small ignition type autotransformer. The primary portion III of transformer 9 is connected in series with the discharge circuit between the terminals 3, 3' and the lamps I, I and the secondary portion I I is connected to capacitive plates I2, I2 located approximately at the mid-points of the glass envelopes of lamps I, I, respectively.

In operation, when line voltage is first applied to terminals 3, 3, the glow switches I, I operate and, after a brief interval, close, which provides circuit continuity through trodes of the lamps. The circuit at this instant may be traced from terminal 3, through the tungsten lamp ballast 2, through primary portion it of transformer 9, through electrode 4, resistance 6, glow switch I, and electrode 5, then through electrode 4', ballast 6, glow switch I and electrode 5 back to terminal 3'. The current flowing through the electrodes causes them to heat up and shortly thereafter switches I and I will have cooled sufiiciently to reopen. Since, due to normal tolerances in manufacturing, no two switches will be identical and open at exactly the same instant, it will be assumed, for ease of explanation, that switch 1 opens first. When this occurs, current is momentarily interrupted in the primary portion Ill of autotransformer 9. The sudden interruption of current therein induces a pulse of voltage in secondary portion I i which is applied by means of the capacitive plates I2 and I2 across the gaseous atmosphere within the lamps I, I. This causes an ionization of the gas within the lamps and the arc strikes in lamp I. Lamp I' is not affected as yet since its starting switch is still closed. When glow switch I opens, a second pulse is generated in the same way and lamp I starts. Both the inductive surge due to the rupture of the primary circuit of transformer 9, and the induced pulse in the secondary, are effective in striking the arc. The purpose of the resistances 6 and 6 in series with the contacts of each glow switch is to limit the preheat current to a value which will not cause an overvoltage condition across tungsten ballast lamp 2 when the glow switches are closed. Under low voltage conditions, where the sum of the striking voltages of the two glow switches approaches or is greater than the line voltage, it may be desirable to shunt one of the switches by a resistance. Thus, placing a resistance 19 (shown in dotted lines) in parallel with switch I, insures that switch I will strike and start lamp I first, after which switch I will strike and start lamp I. Although I have illustrated the arrangement as applied to two lamps, it can obviously be applied to a greater number of lamps with ensuing advantages and economy. Thus, only one pulse coil is required for any number of lamps connected in series across a source. The ignition pulse coil, moreover, generates a high pulse voltage at starting only, so that although the primary portion thereof must be designed to carry the discharge current, the secondary portion may consist of very fine wire since it carries only a negligible current, and that current only at the very instant of starting. Such transformers can be made very small since the energy required to ionize the gas in the lamps with a pulse applied through an external electrode is negligible, being of the order of milliwatts.

the filamentary elec- Referring to Fig. 2, I have illustrated therein another embodiment of my invention which may be utilized to advantage in operating fluorescent lamps from electrical circuits where the terminal voltage is so low as to preclude the use of glow switches. Like reference numerals in this figure denote corresponding circuit elements as in Fig. 1. In this circuit, I have substituted thermal type switches I3 and I3 for the glow switches 1 and of Fig. 1. These switches are thermally associated with a small heating coil or resistance I4 which is inserted in series with the main discharge circuit. Switches I3 and I3 comprise a pair of contacts and bimetallic members I5 and I5, which, upon being heated, bend away from their associated contacts, thereby opening their respective shunting circuits. The remainder of the circuit is in all other respects identical to that of Fig. 1.

The operation of this circuit is similar to that of Fig. l and differs only in the following details: when voltage is initially applied to terminals 3, 3', the thermal switches being in their normally closed position, current flows through the heating coil I4 and also through the filamentary electrodes of the lamps I, I. The bimetallic members of switches I3, I3 heat up and open, the instant of the open circuit occurring at slightly difierent times for each switch in normal course. When either of the switches opens, a pulse is generated which starts the discharge in the lamp associated with that particular switch. When the lamps are lit, the discharge current which must flow through resistor I4 keeps the thermal switches heated and accordingly opened. When the lamps are turned off, the switches gradually cool and, in due course, reclose thereupon assuming the position required for the next lighting operation.

Referring to Fig. 3, the pulse coil therein illustrated shows an actual construction which I utihas to operate two -watt fluorescent lamps of the ordinary commercial variety from a 220-volt alternating current circuit. The dimensions of the coil are 2 length by diameter with primary consisting of turns of No. 28 wire and secondary consisting of 8000 turns of No. 41 wire. This coil demonstrates, in rather striking fashion, the compactness and economy of equipment possible with my invention. The ballast resistance 2 for this particular combination consists of a ZOO-watt, 1l5-volt tungsten filament lamp.

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, the circuit may equally well be used with lamps having but one thermionic electrode when operated from a direct current source; or if two thermionic electrodes are provided, one may be left unheated and the lamp subsequently turned about in its sockets when the first electrode has reached the end of its life. Likewise, while a pulse coil wound as an autotransformer has been illustrated as the transforming means, it is apparent that other well known equivalents may be utilized. The appended claims are, therefore, 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. Starting and operating apparatus for gaseous electric discharge devices having therein spaced main electrodes at least one of which is therm ionic and adapted to be heated by the passage of current therethrough prior to the starting of said devices, comprising a and connections from the outer end of said secondary portion to the auxiliary starting electrodes of said devices.

3. Starting and operating apparatus for low pressure d ischarge lamps having spaced thermages, consequent upon the opening of said switches, to ionize each lamp in turn.

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

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