US2694786A - Preheat neutralizing circuit for fluorescent lamps - Google Patents

Description

Nov. 16, 1954 E. LEMMERS 2,694,786

PREHEAT NEUTRALIZING CIRCUIT FOR FLUORESCENT LAMPS Filed Nov. 25,1949

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United States Patent PREHEAT NEUTRALIZlNG CIRCUIT FOR FLUORESCENT LAlVlPS Eugene Lammers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application November 23, 1949, Serial No. 129,155

4 Claims. (Cl.v 315-97) My invention relates generally to starting and operating circuits for gaseous electric discharge devices of the type commonly known as liuorescent lamps, and more particularly to a cathode preheating and neutralizing circuit therefor which is particularly applicable to small size or low voltage lamps operated without the benefit of a voltage step-up transformer.

The commercially available fluorescent lamps presently on the market may be divided into two generic types, each of which has its own characteristics requiring a particular starting and operating circuit.

The first type is the hot cathode starting lamp which is usually operated with relays or thermal switches to allow preheating of the electrodes to electron-emitting temperatures. For instance, the lamp may be connected across a source of voltage in series with a reactor or ballast, and the activated lilamentary electrodes of the lamp may be temporarily short-circuited by a suitable switch to connect them in series across the source and thereby cause them to be preheated to electron-emitting temperature. Such circuits provide reliable starting,

`operate at good efficiencies, and make for long life of the lamp electrodes. However, they suffer from the obvious disadvantages of requiring a switch as an operating element, which switches must be replaced periodically, and from the relatively slow starting occasioned by the preheating period.

The second type is the cold cathode starting lamp in which the discharge is started directly by means of high voltage transformers without any preheating of the electrodes. Such lamps operate at a voltage much lower than that required for starting; and, accordingly, the transformer unavoidably operates with a relatively high power loss. Moreover, the starting without any preheating of the activated electrodes places them under considerable electrical stress so that their life is appreciably shortened.

in my copending United States application No. 631,381, led November 28, 1945, now U. S. Patent 2,504,548, assigned to the same assignee as the present invention, there are disclosed circuits which combine the advantages of both of the above-mentioned methods of operation. These circuits may be described generically as being of the switchless cathode preheating and neutralizing type, and permit substantially instantaneous starting of uorescent lamps without undue sputtering of their electrodes and with relatively low power loss in their ballasts.

In general, cathode preheating and neutralizing circuits operate on the principle of applying electrode voltage and heating current simultaneously to the electrodes of fluorescent lamps. The heating current provided to the electrodes causes them to arrive quickly at an electron-emitting temperature, whereupon the arc or discharge starts within the lamp. As soon as the discharge has started, the cathode heating current is substantially neutralized by means of changes in the magnitude and phase `of voltages induced in neutralizing or bucking windings connected to the electrodes.

In the afore-mentioned application No. 631,381, the preheating and neutralizing circuit for each electrode comprises two windings, of which one, the heating winding, is inductively coupled to the transformer energizing the lamp; and the other, the neutralizing or bucking winding, is inductively coupled to an inductive ballast inserted in series between the lamp and the transformer.

The present invention is directed towards a circuit of ,the same basic type as disclosed in the aforo-ment1oned application. The circuit herein is more particularly applicable to small `size low voltage fluorescent lamps such as the types which are presently available on the market in power ratings less, than 20 watts, and provides an economical means of operating such lamps with switchless cathode preheating and neutralization without the requirement for voltage ,step-up transformers. Accordingly, it isan object of myinvention to provide a new and improved switchless starting and operating circuit of the cathode `preheating and neutralizing type for fluorescent lamps, in accordance with the foregoing remarks,

In accordance with my invention, the circuit for the lamps comprises a ballast reactance connected in series with the lamp across the alternating current supply and a shunt reactance connected in parallel with the lamp. The ballast reactance and the shunt reactance are each provided with a pair of secondary windings tightly coupled thereto; the secondary windings associated with the shunt reactance serve as heating windings for the lamp electrodes, and those associated with the ballast reactance serve as neutralizing windings in order to eliminate the liow of heating current to the lamp electrodes during operation.

For further objects and advantages and for a better understanding of my invention, attention is now directed to the following kdescription taken in conjunction with the accompanying drawings. The novel features of my invention will be more particularly pointed out in the appended claims.

In the drawings:

Fig. l is a schematic diagram of a cathode preheating and neutralizing circuit embodying my invention as applied to a single fluorescent lamp.

Fig. 2 is a schematic diagram of a similar circuit likewise embodying my invention, as applied to a pair of lamps connected in a lag-lead circuit of a relatively well known type.

Referring to Fig. 1, there is shown a gaseous discharge device 1 which may, for instance, be a fluorescent lamp of the positive column discharge type, comprising a tubular envelope 2 having sealed into its ends a pair of thermionic electrodes 3 and 4. The electrodes are of the two-terminal preheatable type and may consist of coils of tungsten wire activated with the usual mixture of barium and strontium oxides. The envelope 2 contains a rare gas such as argon or neon or mixtures thereof at a pressure of a few millimeters, and a small quantity of mercury. The inside walls of envelope 2 may be coated with a iiuorescent phosphor which, when excited by a discharge through the mercury vapor, emits visible light.

The circuit is connected, through a pair of input terminals 5, 5', to a source of potential, which may, for instance, be provided by the usual 11S-volt, 60 cycle supply mains. The connection to the lamp is made at output terminals 3a and 4a, through a series current limiting inductance or ballast reactance 6. Ballast 6 is preferably in the form of a transformer structure and comprises a primary winding 7 and a pair of secondary windings 8 and 9 in close magnetic coupling therewith.

Connected in parallel with lamp 1 across output terminals 3a, 4a, is a shunt reactance 10 which is likewise preferably provided in the form of a transformer structure, reactance 10 comprising a primary winding 11 and a pair of secondary windings 12 and 13 coupled thereto.

`Each of the electrodes of the lamp is connected in a heating circuit comprising one of the secondary windings of shunt reactance 10 and one of the secondary windings of ballast reactance 6. Thus, electrode 3 is connected across output terminal 3a and its conjugate terminal 3b in a series circuit comprising secondary windings 12 and 8, and electrode 4 is connected across output terminal 4a and its conjugate terminal 4b in a like circuit comprising secondary windings 13 and 9.

When voltage is rst applied to the circuit, relatively little current flows through ballast reactance 6 until the lamp has started. As a result, the voltage drop across ballast reactance 6 is comparatively small and practically 3 the full supply voltage is applied across shunt reactance 10. Reactance 10, accordingly, operates as a transformer and induces a relatively large voltage in its secondary windings 12 and 13 which cause heating current to ow through electrodes 3 and 4. As soon as the lamp electrodes have reached an electron-emitting temperature, the arc starts within the lamp and a relatively large current flows through ballast reactance 6, causing a voltage drop to be produced thereacross which limits the arc current through the lamp to a safe predetermined value. The discharge current flowing through reactance 6 now induces a much larger voltage in secondary windings 8 and 9 than the relatively small voltage which was induced in them heretofore as a result of the current owing through reactance 6 for energizing reactance 10. Moreover, the voltage across shunt reactance 10 is now considerably reduced and in a typical application may be as little as half the supply voltage. Accordingly, the voltages induced in heating windings 12 and 13 are likewise reduced. It will be apparent to those skilled in the art that it is now a relatively simple matter to so proportion the turns ratio of the secondary windings in the two reactances and to provide the required polarity connections such that the voltages induced therein during operation substantially cancel each other. Lamp 1 thereafter operates with substantially no heating current provided to its electrodes as required for normal operation.

It may be noted at this point that complete neutralization of the heating current to the lamp electrodes is not necessary for the successful operation of the circuit. In fact, a small amount of residual heating current is often desirable in order to positively maintain the electrodes at an electron-emitting temperature.

Referring to Fig. 2, wherein the same reference numerals refer to corresponding elements, the same mode of operation is illustrated as applied to a two-lamp lag-lead circuit. Lamp 1 is connected in an identical circuit as in the circuit of Fig. l whereas lamp 1 is connected in a similar circuit which has been modified by the provision of a capacitor 14 in series with ballast reactance 6 and the alternating current supply. Lamp 1 is now connected in a leading power factor load circuit through the phase advancing effect of capacitor 14. However, since the phases of the currents through ballast reactance 6 and through shunt reactance 10 are both advanced by the same amount, the operation of the electrode heating and neutralization circuits will evidently occur in the same fashion as described heretofore.

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 be applied to combinations of lamps and their diverse electrode heating requirements provided by means of additional secondary windings bearing the same coupling relations to their associated main windings as described herein. For example, if in the circuit of Fig. l, it is desired to operate two lamps in parallel, it is obvious that additional secondary windings may be provided in reactances 6 and 10 for each additional electrode which it is required to heat. Likewise, although I have shown the circuit energized directly from the usual 11S-volt, 60-cycle supply, it is apparent that transformers may be utilized to provide suitable voltage transformations where necessary and terminals 5, 5 of the circuit of Fig. 1 connected to such transformers. 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:

l. In combination, a gaseous electric discharge device of the positive column type and comprising a sealed envelope containing an ionizable gaseous atmosphere and a pair of cooperating main electrodes at least one of which is of the thermionic two-terminal preheatable type, an alternating voltage source, a ballast reactance comprising a primary current limiting winding and a secondary winding coupled thereto, means connecting said device and said primary ballast winding in series across said source,

a shunt reactance comprising a primary winding and a secondary winding coupled thereto, said primary shunt winding being connected directly in shunt with said device across its electrodes, and a heating and neutralizing circuit for said two-terminal electrode comprising both said secondary windings serially connected thereacross and in bucking voltage polarity.

2. In combination, a gaseous electric discharge device of the positive column type and comprising a sealed envelope containing an ionizable gaseous atmosphere and a pair of thermionic two-terminal preheatable electrodes, an alternating voltage source, an inductive ballast reactance comprising a primary current limiting Winding and a pair of secondary windings coupled thereto, means connecting said device and said primary ballast winding in series across said source, an inductive shunt reactance comprising a primary winding and a pair of secondary windings coupled thereto, said primary shunt winding being connected directly in shunt with said device across its electrodes, and a pair of heating and neutralizing circuits each comprising one of said secondary windings in said ballast reactance and one of said secondary windings in said shunt reactance connected in series across one of said two-terminal electrodes and in bucking voltage polarity.

3. In combination, a uorescent lamp of the positive column type having a pair of thermionic two-terminal preheatable electrodes requiring heating current at starting and substantially none during operation, an alternating voltage source, a ballast reactance comprising a primary current limiting winding and a pair of secondary windings coupled thereto, said primary ballast winding being connected in series between one side of said source and one of said electrodes, a direct connection from the other side of said source to the other electrode, a shunt reactance comprising a primary winding and a pair of secondary windings coupled thereto, said primary shunt winding being connected directly in shunt with said lamp across its electrodes, and a pair of heating and neutralizing circuits each comprising one of said secondary windings in said ballast reactance and one of said secondary windings in said shunt reactance connected in series across one of said two-terminal electrodes and in bucking voltage polarity, said secondary windings being proportioned such that the voltage induced in one coupled to said ballast reactance during operation opposes and substantially neutralizes during normal operation that induced in one coupled to said shunt reactance.

4. In combination, a pair of gaseous electric discharge devices each of the positive column type and comprising a sealed envelope containing an ionizable gaseous atmosphere and a pair of thermionic two-terminal preheatable electrodes, an alternating voltage source, a pair of inductive ballast reactances each comprising a primary current limiting winding and a pair of secondary windings coupled thereto, means connecting one of said primary ballast windings and one of said devices in series across said source, a ballasting capacitor, means connecting the other of said primary ballast windings, said capacitor, and the other of said devices in series across said source, a pair of shunt reactances each comprising a primary winding and a pair of secondary windings coupled thereto, respective ones of said primary windings being connected directly in shunt with respective ones of said devices across their electrodes, and heating and neutralizing circuits for said two-terminal electrodes, each including a secondary winding of one of said ballast reactances and a secondary winding of one of said shunt reactances connected in series and in bucking voltage polarity across said electrode.

References Cited in the tile of this patent UNITED STATES PATENTS Number Name Date 1,980,534 Kirsten Nov. 13, 1934 2,231,584 Lord Feb. 11, 1941 2,256,242 Edwards Sept. 16, 1941 2,438,564 Lemmers Mar 30, 1948 2,444,408 Larime June 29, 1948 2,504,548 Lemmers Apr. 18, 1950

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