US2438556A - Circuit for electric discharge devices - Google Patents

Description

March 30, 1948. HEHENKAMP 2,438,556

CIRCUIT FOR ELECTRIC DISCHARGE DEVICES Filed Feb. 17, 1943 0 MUCH. 0.0.0.000.

Invenkor: Theodorus Hehenkamp,

His ATTOTIWEBQI Patented Mar. 30, 1948 CIRCUIT FOR ELECTRIC DISCHARGE DEVICES Theodorus Hehenkamp, Eindhoven, Netherlands, assignor, by mesne assignments, to General Electric Company, Schenectady, N. Y., a corporation of New York Application February 17, 1943, Serial No. 476,215 In the Netherlands April 6, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires April 6, 19.60

3 Claims.

My invention relates to circuits for electric discharge devices, and more particularly to circuits for devices employing filamentary electrodes such as fluorescent lamps.

It is known to connect the series-connection of a serially-connected condenser and a choke coil to a source of alternating current, and to bridge the condenser by the series-connection of another choke coil and a gas-discharge tube, the first-mentioned choke coil, which may also be divided, for example into two portions, and the condenser being so dimensioned that between the terminals of the condenser there is set up a high voltage which ignites the discharge tube.

This device has very satisfactory properties not only as regards the ignition but also the operation of the discharge tube. Thus, for example, it is possible to obtain with this device a very satisfactory power factor which may be even substantially equal to unity. Furthermore, it is easy to obtain the advantage that the higher harmonics produced by the discharge tube can penetrate to the source of current only to a slight extent and that the device is slightly sensitive to the voltage variations occurring in sources of current.

One drawback of this prior art device resides, however, in that upon the closure of the switch with the aid of which the device is connected,

to the source of current a high voltage is set up across the terminals of the condenser and in other parts of the device even when the discharge tube is not in its holder or holders. At the same time a heavy current passes in this case through the condenser and through the choke coil connected in series therewith. In this case there exists the danger that when one forgets to open the said switch again this high voltage and this heavy current remain in existence, which not only implies an unnecessary loss of energy but also may lead to deterioration of the device.

A further drawback of the known circuit arrangement is seen in that if the discharge tube comprises incandescent electrodes, and if it is desired to heat the latter prior to the ignition of the discharge tube, it is necessary to take particular steps, which complicate the device.

In devices wherein all the auxiliary elements required for the ignition and the operation of the gas-discharge tube are connected in series, these drawbacks may be avoided by incorporating the incandescent electrodes or a conductive bridge provided in the cap or caps of th discharge tube in this series connection so that tilting state.

only the discharge path of the discharge tube is located in parallel with a portion of the seriesconnection. The properties of these devices differ, however, from those of the first-mentioned device wherein the series connection of a choke coil and a discharge tube is located in parallel with a condenser which in turn is connected in series with another choke coil.

It is, however, impossibledirectly to modify the last-mentioned device in such manner that all the auxiliary elements are connected in series since in this circuit-arrangement there is a particular point of junction, viz. a point which is connected not only through a choke coil to the discharge tube but also through two branch circuits to the two terminals 01 the source of current.

A circuit arrangement of this kind which comprises such a point of junction connected through a choke coil to the tube, will hereinafter be shortly referred to as junction-point system.

Such a junction point also occurs in other devices comprising gas-discharge tubes. It is known, for example, to connect a gas discharge tube in series with a choke coil to a source of alternating current and to mount in parallel with the tube plus the choke coil a condenser which has for its purpose to reduce the phase lag of the current taken from the source of current or even to convert it into a lead. Here again arises the drawback that when a voltage is applied to the device while the discharge tube is not present in the latter, a current flows through the condenser, which means a useless load on the source of current with a greatly leading current. Besides, also in this device the incandescent electrodes which the discharge tube may comprise cannot be heated prior to the ignition without taking particular steps.

A further case wherein such a junction point is present occurs with a device wherein a condenser and a choke coil are connected in series with on another to a source of current and the series-connection of a gas-discharge tube and a choke coil is located in parallel with the firstmentioned choke coil, this choke coil and the condenser being so dimensioned that with the non-ignited discharge tube, due to the saturation of the choke coil which occurs in this case, a very heavy current flows through the circuit and consequently there prevails between the ends of this choke coil a high voltage which ignites the discharge tube whilst after the ignition oi the discharge tube the said circuit leaves the If a voltage is applied to this dedifferent intensities.

vice while the discharge tube is not present a heavy current flows permanently through the condenser and the choke coil due towhich they can easily be deteriorated. Furthermore, in this device heating of the electrodes prior to the. ignition of the discharge is impossible withoutfurther steps.

The invention has for its object to obviate the;

above-mentioned drawbacksof such devices in which there is a similar pointof. junction and to retain at the same time the .electric properties, of these devices.

The device according to the invention corresponds t known junction-point systems in-thatit comprises a discharge tube which is provided iliary electrodes) and eac'h'of whichcomprises' two current supply members (AandB, C and D.

respectively) whilst the .membersAis connected" through a choke coil and,v as the case'may'be, through another impedance to a terminal of a source of alternating current? and." the member C is'connected, as the case-may be, through an impedance to the second-terminal ofv this source of. current.

According; to the presentinvention; the choke coil comprises an auxiliary winding and the memberBis connected throughthisauxiliary winding and'an'i impedance to the member D, the. auxil-"- iary winding being wound in such manner that" upon the passage of a series-current through the main winding and the auxiliary winding of. the? choke coilmagnetic fields are generated which counteract one another.

' stituted thereby. The choke coil 9' mayalso In this device all the auxiliary elementsand both-conductive bridges present in or on the discharge tube are connected in series so:that,.

when--thedischarge tube is removed from the: holders, the circuit is necessarily interrupted. If th'esaid bridges constitute the incandescent elec-- trodes or the heating elements of the (indirectly heated) incandescent electrodes, these 'elec'- trodesor-their heating elements are directlypresent in the series-connection formed and 'they' are heated prior to the ignition of the discharge.

In this way we obtain the advantages of theseries-connection of the auxiliary elements; 'at the same time, however, owing to the use of the. auxiliary winding provided in a particular manner on the choke coil we obtain properties which are.

abse'ntin the hitherto knownldevices comprising auxiliary elements connected'in series and which correspond to the properties of junction-point systems. detail in the description of the form. of construction given by wayof example.

'Thechoke coil may be, at least partly, bifilarly wound. During normal operation there pass through the two windings in general currents of Due to the fact that bifilar winding with Wires of difierent. thicknesses requires an excessive winding space, it may be advantageous to constitute the. windings by stranded wire of which a determined number ofconcluctors are incorporated in the main winding and the remainder in the auxiliary Winding.

' gas-discharge tubes are meant hereinafter This Willhereinafter be explainedfim one or more gases but also tubes which contain a fillingof vapour or Qf a..mixtur,e of gas and vapour. I

The invention will be explained more fully with reference to the accompanying drawing which represents diagrammatically,by way of example; one embodiment thereof.

In the drawing, l denotes a discharge tube serving for the radiation. of light, which is constituted bya tubeihaving, for example, a length of 100' cms. and a diameter of 3.5 cms. and which .comprisesitwo thermionic electrodes 2 and 3 provided with a substance of high electron-emissivity; The lamp contains a filling of rare gas, for

exam-pleargon, at a pressure of a few mms. of mercury and, inaddition, a small quantity of mercury which exhibits during operation a lowpressure mercury vapour discharge with a positive column. The inner surface of the wall of the tube may be coatedzwith a luminescent substance which is excited to; luminescence by-i'the ultra-violet rays:generated vin: the discharge: ,It: is, of. course, also possible'to'rutilize-in the device dischargestubes: of.

according to the invention other type.- V

Each of; the-incandescent electrodes-2 and 3' is provided withtwoncurrent supply; membersv 4, 5.-and 6, 'l'respectively which correspond to' the above-mentioned members AD.". The member iof :the electrode 2 iscOnnected. through a choke coil winding 8 and; a chokecoil-fi to the terminal lilo-f a sourceof alternating'current whilst; the

member f the; electrode -3-is. connected through:

theintermediary of, a. switch: H to-theother terminal lzofthe said. sourceof current. It thesource of current is constituted bya leakage transformer or by a-g enerator having a .high self inductive reactance, the choke coil 9 may be subconsist of two. portions ofwhich the-onemay be incorporated. in the circuit arrangement at the point'shown and the; other between the switch I l and the members- The current supplymember =5 of theelectrode. 21is connected through .a windin iafland arcon. denser M to the member 1 of the electrode-=3...

The winding l3 constitutes the auxiliary windingof the choke coil o-fwhich 8 isthe :principal V The auxiliary windingll has been wound in such manner thatprior tothe estab winding.

lishment of adischargebetween the electrodes 2 and3the. windings 8 and 13 counteract oneanother.. I 7

With the interposition of the heating elements of the incandescentelectrodes and-3the in- I d-uctive elements 9, .8 and l3'andthe capacitative element I4; are. connected-in .series with one another and are so dimensioned that between the electrodes there occurs a'voltage which is sufficient for, the ignition of thetube; Owing to the fact that the current flowing through this ci-rcult-arrangement raises the electrodes; prior=to the. ignition, to .the temperatureeof emission, the

required ignition voltages; acquires a lowervaluethan is the casewith electrodes. v

After the switch. I [has :been .closed, the maga tube comprising cold netic fields generatedbythe windingstand I3 counteract one another so that in the casewherein they have been chosen so as to be mutually equal the voltage suppliedto the tube, I; is -sub-= stantially equal to the voltage across the condenser M and, as it were,.ashort-circuiting connection is producedbetween the points l5 311C113.

a -g h L w or the wine ings 8 and I3 is, however, not necessary as experiments have shown.

After the tube I has been ignited, neither the intensity nor the phase of the current passing through the winding I3 are in general equal to those of the current flowing through the winding 8. It has been found that there need not exist any appreciable potential diiTerence between the points I5 and I6. Thus we obtain a device which has, so to speak, interconnected points I5 and I6 and, instead of the windings 8 and I3, a single choke coil with all the concomitant good qualities in operation.

By providing the auxiliary winding I3 it is consequently possible to give the device, wherein all the auxiliary elements are connected in series, the properties of a junction-point system without the possibility of giving up pre-heating of the electrode and interruption of the seriescircuit upon the removal of the discharge tube from its holders.

It has been found by testing that it is not absolutely necessary to form the winding I3 in such manner and to couple it with the winding 8 so tightly that even when the discharge tube is operating there exists between the points l5 and I6 substantially no potential difference at all. Also in the case of a less tight coupling of the windings I3 and 8, in which event a potential diflerence of a few tens of volts was set up, between the points I5 and I6, it proved to be possible to obtain, at least to a large extent, the properties of the junction-point system.

In one concrete case the elements of the device had been so chosen that at a mains voltage of 220 volts and 50 cycles prior to the ignition of the tube the joint current passing through all the elements amounted to 0.4 amp., whilst the voltage across each electrode was 12 volts and the voltage between the electrodes was 350 volts; With the tube in operation the current taken from the mains was 0.14 amp., the current flowing through the condenser was 0.225 amp. and the discharge current was 0.25 amp.

The two-wire choke coil 8, I 3 was provided with an iron core having an air gap with a cross-sectional area of 3.7 sq. cms. and a length of 0.04 cm. The winding I 3 consisted of 1460 turns of copper having a diameter of 0.28 mm. and the winding 8 consisted of 1360 turns with a thickness of 0.2 mm. The winding I3 was arranged around the winding 8. In spite of the fact that the total current passes through the winding 8 it was possible to take for the latter a thinner wire than for the winding I3.

With the tube in operation there occurred across the elements of the device the following voltages: 77 volts across the choke coil 9, 146 volts across the winding 8, 2 volts across each of the incandescent electrodes, 149 volts across the winding I3, 198 volts across the condenser I 4 and 103 volts between the electrodes. The potential difference between the points I5 and I 6 was in this case 9 volts and the power factor of the device was 0.94 lagging.

Owing to the tight coupling between the windings the potential difierence between the points I5 and I5 is slight. It has been found, however, that with a less tight coupling with which the winding 8 and I3 were arranged side by side and there existed between them a leakage field of such intensity that the voltage between the points I5 and I 6 increased to 57 volts no appreciable change in the operation of the device occurred.

The application of the invention is, of course,

last-mentioned choke coil may also be so dimensioned that, prior to the ignition of the tube, it is tilted over, in co-operation with the condenser which has been substituted for the element 9, into a state of high current intensity but leaves this tilting state when thetube is operating.

The invention may furthermore also be advantageously utilized in order to avoid more than one junction-point, Such is the case, for example, when between the member 6 and the switch I I there is achoke coil which corresponds to the choke coil 8 and which is provided in this case with an auxiliary winding which is connected between the member I and the condenser I4.

In the form of construction described by way of example, the conductive bridges incorporated in the series-connection of the auxiliary elements are formed by the electrodes 2 and 3. The discharge tube may also be provided with two main electrodes, in which event an auxiliary electrode is provided in the neighborhood of each main electrode. The main electrodes are connected in this case to the current supply members 4 and 6 respectively whilst the auxiilary electrodes are brought into connection with the current supply members 5 and 1 respectively. When the device is put into operation, auxiliary discharges are established between each main electrode and the neighbouring auxiliary electrode. These auxiliary discharges, by which the main electrodes are heated, are in series with the auxiliary elements and form the'conductive bridges above referred to. Here again the circuit is always interrupted when the discharge tube is not in its holders.

The invention may also be applied when the discharge tube comprises two electrodes which are not heated prior to the ignition of the discharge. In this case the conductive bridges between the members 4 and 5, and 6 and 'I respectively may consist, for example, of two conductors present in the caps of the discharge tube.

What I claim is:

1. In combination, an alternating current supply circuit, an electric discharge device of the type employing an ionizable medium and including a pair of filamentary electrodes each having a pair of terminals, means comprising an inductive choke having a main winding connected in series with one terminal of said source and one terminal of one of said electrodes and an inductively coupled auxiliary winding connected to the other terminal of said electrode, means for connecting the auxiliary winding to a terminal of the other electrode, and means for connecting the other terminal of said other electrode to said supply circuit, said main and auxiliary windings being wound in such manner that upon the passage of series current therethrough opposing magnetic fields are produced.

2. In combination, an alternating current supply circuit, an electric discharge device of the type employing an ionizable medium and including a pair of filamentary electrodes each having a pair of terminals, means comprising an inductive choke having a main winding connected in series with one terminal of said source and one terminal of one of said electrodes and an inductively coupled auxiliary winding connected to the other terminal of said one electrode, a capacitor commentedv i-n seriesrelationawith said: auxiliary winding-angliconnectedto arrtermi al Ofrthe other electrode; and means for connecting the other terminator :saidotherelectrode to said pply circu t, isaid ma n: and: -;au aryr windin s being wound to produc counteracting magnetic fields uponthe passage ofr series current; therethrough.

' 3; In combinati0n,,;an{alternatingcurrent supply circuit, an elec ylfic clischarge device of the type employing {an ionizable'medium and. including a pair of filamentary electrodes each having a pair of ;temn-i-nals,,means comprising an inductive choke having; amain winding connected in series with one terminator said. source and one terminal of one ofjsaid electrodesand an inductively coupled auxiliary-winding connected to the other terminalyof saidpne; electrode, a capacitor connect-ed in series relation with said auxiliary Winding-and -connected-;tozaterminal of. the other electrode, and means for connecting the other,

REFERENCES omen The following references are of-record. in the file of this patent: V

FOREIGN PATENTS Country Date Number v Australia June 10, 1942

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