US2346621A - Alternating current supply system - Google Patents

Description

April 11, 1944. so 2,346,621

ALTERNATING CURRENT SUPPLY SYSTEM Filed NOV. 13, 1943 2 Sheets-Sheet 1 Invent 0r db gepk 60262;

April 11, 1944. J, G, SOLA ALTERNATING CURRENT SUPPLY SYSTEM 2 Sheets-Sheet 2 LX112 4x5- IIHH 55 HUN MEG. I

Patented Apr. 11, 1944 ALTEBNATING CURRENT SUPPLY SYSTEM JosephG. Sola, Western Springs, 111., asslgnor to Sola Electric o.I Chicago, 111., a corporation of Delaware Application November 13, 1943, Serial No. 510,117

9 Claims.

This invention relates to alternating current supply systems for consumption circuits having negative resistance characteristics, more particularly the invention relates to self-regulating systems for supplying alternating current at substantially unity power factor to load devices requiring high starting voltages and having resistance characteristics which vary inversely with the operating current flowing therethrough, and the invention has for an object the provision of improved, inexpensive and reliable systems of this character. V

While the invention is not limited thereto, it is particularly applicable to and will be described in connection with gaseous discharge tubes, such, for example, as cold cathode fluorescent tubes for lighting purposes. Although cold cathode tubes of the fluorescent type have heretofore been known, the tendency in the lighting art has been toward the use of hot cathode tubes due principally to the difllculties encountered in supplying cold cathode tubes with the necessary high voltage for ignition and thereafter controlling the operating current supplied thereto.

It has heretofore been proposed to supply such tubes through a high reactance transformer having a sufllciently high secondary voltage to ignite or start the current flow in the tube, the transformer being so designed that the secondary voltage decreases with increasing current flow until a stable condition exists. The transformer reactance acts as an inductive ballast in the circuit and thus an undesirable low power factor current is drawn from the source of supply. Furthermore it has been found that if the transformer is designed to supply an initial secondary voltage only high enough to insure breakdown .or starting of the tube, the current flow will be stabilized at values considerably less than the optimum values necessary for the most efllcient operation of the tube, and accordingly the illumination produced by the tube falls far short of its maximum capacity.

To increase the initial or open circuit voltage of the transformer'to a higher value in an attempt to reach a stable condition'wlth the optimum current flowing in the tube results in such a bulky and expensive transformer structure as to be undesirable, and in addition the higher open circuit voltage gives'rise to insulation problems which increases the expense and may result in danger to the user.

The use of condensers connected in parallel with the tube across the secondary winding for power factor correction purposes has also been suggested, but this expedient is ineffective in reducing the size or cost of the transformer and in fact adds to the size and cost of the apparatus because of the size of the condenser necessary to balance the inductance of the transformer. Accordingly, much is yet to be desired in supply systems for load devices of this character having negative impedance characteristics, and it is a further object or this invention to provide a supply system for cold cathode type tubes employed for illumination purposes which is compact, in-

,exmnsive and reliable, which is self-regulating,

and which will supply an optimum operating current to the tube at substantially unity power factor.

In my prior Patent No. 2,143,745, issued January 10, 1939, there is described and broadly claimed a constant voltage transformer capable of general application which employs a high reluctance magnetic shunt for effecting a relatively loose coupling between the primary and secondary sides in combination with a resonant circuit in the secondary side for maintaining the secondary voltage substantially constant over a wide range of primary voltages. In my later patent, No. 2,212,198, issued August 20, 1940, an additional current-limiting winding and high reluctance shunt are employed, in co-operation with a resonant circuit and shunt similar to that described in my Patent No. 2,143,745, in'order to provide a limited current supply to a tube or similar load device having a negative resistance characteristic.

In carrying out the present invention, I employ certain of the basic principles set forth in my above referred to patents, but the various elements of my improved systems are differently connected and are so arranged and proportioned as to provide improved, more compact and more economical systems particularly intended for supplying load devices such as cold cathode fluorescent tubes having negative resistance characteristics. Thus I provide, in accordance with one embodiment of my invention, a transformer having primary and secondary windings adapted to be respectively connected to an alternating current source of predetermined frequency and voltage and to a load such as a cold cathode tube having a negative resistance characteristic. The transformer includes a high reluctance shunt magnetically disposed between the windings, which shunt is substantially ineffective when no current flows in the secondary circuit of the transformer, the shunt functioning upon the new of current in the secondary winding to divert part of the flux produced in the transformer core by the primary and secondary currents and thus to relax the coupling between the windings. Connected in series circuit relation with the secondary winding and the load, I provide a condens er having a capacity reactance so proportioned, relative to circuit constants of the transformer and the load, as to resonate with the secondary winding and provide in the secondary load circuit an oscillatory condition of a series resonant nature. The primary and secondary windings may be electrically separate or may be connected together in auto-transformer relation, as desired, and a plurality of secondary windings for supplying separate loads may be associated with a single primary winding, each secondary winding being serially connected with a suitable condenser and load. In the latter case a suitable shunt will of course be magnetically disposed between each secondary, winding and the common primary winding,

For a more complete understanding of my invention, reference should now be had to the drawings in which:

Fig. 1 illustrates a suitable coil and core structure which may be employed in systems embodying my invention;

Fig. 2 is a somewhat schematic wiring diagram showing one system of circuit connections which may be used when the core and coil arrangement of Fig. 1 is employed in carrying out my invention;

Fig. 3 is a somewhat diagrammatic view similar to Fig. 1 but showing another coil and core arrangement;

Fig. 4 is a circuit diagram of a system embodying my invention and employing the coil and core arrangement of Fig 3; and

Fig. 5 is a vector diagram showing the phase relations of the voltage which may exist in the secondary circuit of a system embodyingmy invention.

Referring now to Figs. 1 and 2 or the drawings, I have shown my invention as embodied in a system which comprises a coil and core arrangement or transformer l including a center core I l formed of a stack of suitable laminations on the opposite ends of which are mounted a primary winding l2 and a secondary winding l3. In order to provide suitable magnetic return paths for the center core ll, an outer frame is provided having end legs I 4 and I and upper and lower side legs I6 and H, the end legs l4 and f5 being preferably notched out as shown to receive the opposite ends of the center core II. The outer frame is of course formed of a suitable stack oflaminations and, as shown, the side legs l6 and shown as being of the shel1 type, it will of course be understood that other core and coil arrangements may be employed so long as a high reluctance shunt magnetically disposed between the Fig. 2 by the'reference numeral 25, and the secondary winding 13 is provided with suitable connecting leads 26 and 21.

In Fig. 2 my improved alternating current supply system is shown as applied to a negative resistance load which is indicated somewhat diagrammatically as constituting a cold cathode tube 28 which may be of the fluorescent type known in the art and adapted to be employed for lighting purposes. As shown in Fig. 2, one electrode of the tube 28 is connected to the lead 26 extending from one sheet the secondary winding l3 and the other electrode of the tube 28 is connected by a conductor 29 to a condenser 30, the other side of the condenser being connected to the lead 21 which extends from the other side of the secondary winding l3. Thus the secondary winding l3, the condenser 30 and the tube 28 are com nected in a closed series circuit.

As will be more fully explained hereinafter, the

- circuit constants of the transformer In, particuval H are provided with inwardly extending shunt portions which cooperate with oppositely extend- 7 ing shunt portions on the center core II to provide magnetic shunts l3 and I9 between the windings l2 and 13. The shunt portions on the outer frame terminates short of the corresponding shunt portions on the core I I so as to leave air gaps 22 of predetermined size in the magnetic shunts.

It will of course be understood that the mag-- netic shunts l8 and I9 between the windings may be formed entirely by shunt portions which extend inwardly from the outer frame legs, or

entirely by shunt portions which extend out-- wardly from the center core portion H. In either case, however, a small air gap should be provided in order to provide the desired high reluctance in the shunts. Although the transformer I0 is larly the secondary winding thereof, and the circuit constants of the-condenser 30 are so proportioned relative to the circuit constants of the tube 28 as to insure an optimum fiow of current through the secondary circuit. Preferably, the circuit constants are so proportioned as to provide an oscillatory condition in the nature of series resonance in the secondary circuit such that the optimum value of current will flow through the load, the value of the current flow being limited by the resonant condition of the secondary circuit and the permeability of the iron core regardless of the negative resistance characteristic of the load. The optimum value of current is maintained substantially constant regardless of-varlations in the voltage applied to the primary winding i2-from the source 25.

In the embodiment of the invention shown in Figs. 3 and 4, a pair of secondary windings 3i and 32 is associated with a single primary winding 33. In this embodiment the center core 34 of the transformer 35 is provided with two sets of outwardly extending shunt portions, and the upper and lower legs 38 and 39 of the outer magnetic frame are provided with corresponding sets of 1 supply a separate load circuit, are connected in auto-transformer relation with the primary winding as shown in Fig. 4. Thus the primary winding 33 is connected by means of suitable conductors 42 and 43 to a source of alternating current voltage of predetermined frequency indicated by the reference numeral 36. One terminal of the secondary winding 32, as shown in Fig. 4, is connected by a suitable conductor 44 to the conductor 42 leading to one side of the primary I winding 33, and the other terminal of the secondary winding 32 is connected by a conductor 45 to one terminal of a suitable load device or tube 46, the other terminal of the load'device 46 being connected by a conductor 41 to a conaacacar denser II, which in turn is connected to the conductor 42 leading to the other terminal of the primary winding a. In this manner the primary winding 23 and the secondary winding 22 are connected in auto-transformer relation in series circuit with each other and with the load device or tube 40 and the condenser 48.

Similarly, the secondary winding 2| is connected at one end by a conductor I to the conductor 42 leading to one end of the primary winding 22, and the other end of the secondary winding Ii is connected by means of a conductor ii to one terminal of a load device or tube 52, the other terminal of the load device being connected through the conductor 58 to a condenser 54, which in turn is connected by a conductor 55 to the conductor 42 leading to the opposite terminal of the primary winding 22.

It will of course be understood that the transformer Id of Fig. 1 may have its secondary winding connected in auto-transformer relation to the primary winding, and likewise the transformer 35 of Fig. 3 may have each or its secondary windings connected to its associated condenser and load in electrically insulated relation to the primary. In each case, however, the windings must be properly proportioned for the particular type of connection employed.

In describing the operation of systems embodying my invention, reference will first be made to the system shown in Figs. 1 and 2. When the primary winding i2 is first connected to the source of energy 25, a magnetic flux flows through the core II and the return paths provided by the end and side legs l4, l5, l8, and H of the outer frame so as to thread through the secondary winding is and induce a voltage therein. Since the cold cathode tube 28 is initially nonconducting the secondary circuit is effectively open circuited and neither the condenser 30 nor the magnetic shunts l8 and is will substantially eifect the value of the secondary voltage. Due to the high reluctance of the air gaps 22 only a very small amount of the primary flux will flow through the shunts and consequently a secondary voltage substantially equal to the tum-ratio voltage of the transformer ill will be applied to the tube 28.. This tum-ratio 'voltage is so chosen as to eiIect breakdown or ignition of tube 28 to render the tube conducting, whereupon a substantial current immediately flows between the electrodes of the" tube to produce the desired illumination.

Immediately upon the now of current in the secondary circuit the condenser 30 and the magnetic shunts become effective to establish a stable self-regulating condition in the secondary circuit whereby an optimum value of current is established and maintained without regard to the negative impedance characteristics of the tube and without regard to variation of the primary voltage over a substantial predetermined range. The capacity reactance of the condenser 30 is preferably so proportioned relative to the efiective inductance of the secondary winding l3 and the impedance characteristics of the tube 28 upon the flow of current in the secondary circuit, as to produce an oscillatory condition in the nature of series resonance in the secondary circuit. Moreover, as soon as current flow begins in the secondary winding II, a back magneto-motive force is produced in the section of the core ll surrounded by the secondary winding which tends to oppose the flow of primary flux therethrough, and accordingly a part of the primary flux is directed through the shunts II and It so as to reduce or relax the coupling between the primary and secondary windings.

It is a known characteristic of series resonant circuits that the current flow therein is limited primarily by the resistance in the circuit, the inductive reactance and the capacity reactance in the circuit being substantially equal and opposite. Consequently, the current is substantially in phase with the voltage and substantially unity power factor is obtained. In my improved system the magnetic core l0 and the windings l2 and II are so designed as to operate substantially at the maximum flux density of the secondary section of the core with the optimum value of current flowing through the tube and with a series res-' onant condition in the secondary circuit. It has been found that following initial breakdown of the tube 28 the secondary voltage, instead of dropping as is the case with the usual high leakage reactance transformer employed for igniting such tubes, rises to a higher value at which a stable condition is reached with optimum current flow through the tube, which stable condition is determined by the oscillatory condition of the secondary circuit and the maximum flux density condition of the iron core. If the resistance of the tube 28 tends to decrease, by reason of its negative characteristic, an increase in current is prevented by the fact that the iron of the secondary circuit is already at its maximum flux density, and consequently the current flow is maintained at the desired. optimum value regardless of the negative resistance characteristic. Operation of the iron at its maximum flux density is permissible, since the inductive reactance oi the secondary winding is not utilized as a ballast for absorbing the excess voltage in order to limit the voltage drop across the tube.

As soon as the oscillatory or series resonant condition is established in the secondary circuit, the flux density in the secondary portion of the core II rises to a value greater than the flux density in the primary portion. Accordingly, as the flux density in the primary portion varies with variations over a wide range in the voltage applied to the winding i2, the flux density in the secondary core portion will vary only slightly since more or less flux will be by-passed through the magnetic shunts according to the character of the voltage change on the primary. Thus the secondary voltage component applied to the tube 28 remains substantially constant over a wide range of voltage variation on the primary wind- 5 ing, insuring constant illumination by the tube.

Fig. 5 is a vector diagram iriustrating a set of voltage conditions which may occur, with properly selected circuit constants, in the secondary circuit of a supply system embodying my invention. The current, which of course is the same in all parts of the series circuit, may be represented by a vector (not shown) lying along the broken line 60 in Fig. 5. The voltage across the secondary winding is accordingly indicated by the vector IXL, which represents the inductive reactance drop out of phase with respect to the current, and by the small vector IRL which represents the resistance drop in phase with the current. Similarly, the voltage across the condenser .is indicated by the vector IXc 90 out of phase with the current and out of phase with the voltage IXL. The load, which in this case is a cold cathode tube, has in addition to its pure resistive impedance a substantial capacity reactance, and accordingly the voltage drop across ant secondary voltage represented by the vector 12 is slightly out of phase with the current, the current leading the resultant voltage. It will of course be understood that a series resonant condition does not require that the inductive and capacitative reactance of the circuit be exactly equal or that the current and voltage be exactly in phase so as to provide unity power factor.

The slightly leading current condition shown in Fig. is well within the range of resonant operation and provides a power factor in the neighborhood of unity. If exact resonance and unity power factor are desired, it is only necessary to correlate the capacity reactances of the condenser and tube so that their sum will be equal to the effective inductive reactance of the secondary winding with the optimum value of current flowing in the secondary circuit.

Although my inventionis not limited to any specific dimensions of the iron cores and the windings, or to any specific loads or condensers, but rather contemplates the correlation of the various circuit'constants in accordance with the voltage and frequency of the source and the current and voltage rating of the load, the following specifications, which are given merely by way of example, may be employed in constructing a system for energizing 40 watt cold cathode type fluorescent tubes adapted for optimum operation with a current flow of approximately 120 milliamperes. A core structure such as is shown in Fig. 3 may be provided having the center c0re 34 composed of a stack of laminations approximately 3% inch by inch in cross section, with the outer frame legs 38 and 39 about one-half as large in cross section as the center core, the shunts 40, and'll approximately of the same cross section asthe outer frame legs, and the gap in the shunt paths approximately .050- (fifty thou- 'sandths) of an inch-in.width.-

On this core. structure may be placed the single primary winding 33,.composcdof 1000 turns of The secondary windings are connected in autotransformer relation to the primary winding, as shown in Fig. 4, andthe condensers 48 and 54, connected as shown in Fig. 4, should have a capacitance" or .4 microfarad.

It was found that the transformer, when thus constructed, produced on open circuit a secondary voltage of approximately' '.600 volts, somewhat less than the'turn-ratio' voltage, with the primary winding connected to a fioflcyclesource of energy 5 at approximately. LIB-volts.

Upon closure'of the primary circuit with the 40 watt tubes connected as shown, it was found that the tubes would be ignited and would immediately operati eat full brilliance with a current No. 26 wire', and the --two secondary windings 3i and 32 each composed of 4600 turns of No. 32 wire.

'tially perfect regulation and constant found to be approximately 90,000 lines per square inch.

Tests for temperature rise under short circuit showed a maximum temperature rise of 26 C. in the primary and 38 C. in the secondaries, and the emciency of the systems was found to be approximately 82%. When the primary voltage was varied between 106 and volts substanlight output was observed, the maximum variation being less than 1 It will be apparent from the above description and the illustrative example thatI have provided a highly efllcient, compact and economical transformer and supply system for cold cathode tubes, or similar loads having a negative resist ance characteristic, which is self-regulating and which provides optimum operation of the load over a wide range of variation in the supply voltage, and which operates at substantially unity power factor.

A transformer built in accordance with the above specifications, not only provides more eflicient operation and better regulation than has heretofore been obtainable, but in addition represents a great saving in materials weighing only one-third as much as the high-leakage reactance transformers heretofore employed for supplying equivalent tubes or loads.

While I have shown particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made,'and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In an alternating current supply system; the combination with an alternating current source ofpredetermined voltageand frequency; of a gaseous discharge tube having a high initial breakdownvoltage and a negative impedance operating characteristic; a transformer including magnetic core means having primary and secondary core portions; said portions having primary and secondary windings associated therewith respectively connected across said source and said tube; said windings having a turn ratio such that the open'circuit voltage of said secondary winding is sufficient to effect initial breakdown of said tube; said core means including a high reluctance shunt magnetically disposed between said windings for relaxing the coupling therebetween upon the flow of current in said secondary winding; said core means'and said secondary winding being so proportioned that said secondary core portion operates at substantially maximum flux density upon the flow of a secondary current corresponding to optimum operation of said tubes; and capacity reactance means in series circuit relation with said tube and'said secondary winding; said capacity reactance means, said secondary winding and said tube having impedances at said frequency so proportioned as to effect a stable oscillatory condition of operation in the secondary circuit upon breakdown of said tube thereby to increase the secondary voltage and cause said optimum current flow through said tube; said current being limited by said maximum flux density regardless of said negative impedance characteristic of said tube.

2. In an alternating current supply system, the combination with an alternating current source ofpredetermined voltage and frequency of a gaseous discharge tube having a high initial breakdown voltage and a negative resistance operating characteristic, a transformer including primary and secondary windings disposed on a closed magnetic core and having a magnetic shunt disposed between said windings, a condenser, and means connecting said condenser in series circuit relation with said secondary winding and said tube, said windings having a turn ratio such that the open circuit voltage of said secondary winding is sufficient to effect initial breakdown of said tube and said shunt'being effective upon the flow of current in the secondary circuit to vary the degree of coupling between said primary and secondary windings, said shunt and said secondary winding being so proportioned and arranged relative to said condenser and said tube as to establish in said secondary circuit a stable oscillatory condition of a series resonant nature when said primary winding is energized from said source to produce a current flow in the secondary circuit corresponding to optimum operation of said tube, the magnetic flux in the secondary section of said core corresponding substantially to the maximum flux density of the secondary section of said core upon the flow of said optimum current whereby said current flow is limited to said optimum regardless of said negative resistance characteristic of said tube.

3. In an alternating current supply system, the

combination of a gaseous discharge tube having a high initial breakdown voltage and a negative resistance characteristic, a transformer including primary and secondary windings and a magnetic shunt disposed therebetween, a condenser, and means connecting said condenser in series circuit relation with said secondary winding and said tube, said windings having a turn ratio such that the open circuit voltage of said secondary winding is sufiicient to effect initial breakdown of said tube and said shunt being effective upon the flowof current in the secondary circuit to vary the degree of coupling between saidprimary and secondary windings, the respective impedance characteristics. of said secondary winding, said produce in said secondary circuit a current flow corresponding to optimum operation of said tube, said current being limited to said optimum value by the maximum flux density of said core, regardless of said negative resistance characteristic of said tube.

5. In an alternating current supply system, the combination with an alternating current source of predetermined voltage and frequency, of a gaseous discharge tube having a high initial breakdown voltage and a negative impedance operating characteristic, a transformer including magnetic core means having primary and secondary portions, said portions having primary and secondary windings associated therewith and respectively connected across said source and said tube and having a turn ratio such that the open circuit voltage of said secondary winding is sumcient to effect initial breakdown of said tube, said transformer including a high reluctance shunt magnetically disposed between said windings for relaxing the coupling therebetween upon the flow of current in said secondary winding, said core means and said secondary winding being so proportioned that said secondary core portion operates at substantially maximum flux density upon the flow of a secondary current corresponding to optimum operation of said tube, and capacity reactance means connected in series circuit relation with said secondary winding and said tube proportioned to resonate with said secondary winding to produce said optimum current flow.

6. In an alternating current supply system, the combination with an alternating current source of predetermined voltage and frequency, of a gaseous discharge tube having a high initial breakdown voltage and a negative impedance operatcondenserand said tube at the frequency of energization of said primary winding and the coupling provided by said shunt beingso proportioned that'a substantially-series resonant eondition is effected in said secondary circuit and said transformer is operated at substantially its'max irnum flux density in the secondary section thereoi' whereby a limited but optimum current flows through said tube regardless of the negative resistance characteristic thereof.

4. Inan alternating current supply system, the combination with a substantially constant frequency alternating current source, of a; gaseous discharge tube having a-highinitial breakdown voltage and a negative resistance operating characteristic, magnetic core means providing a'substantially closed magnetic path, primaryand secondary windings 'on said -core means in magnetically coupled relation,- said core means including a high reluctance shunt interposed magnetically between said windings whereby the flux threading through one winding may greatly exceed the flux through the other, and a condenser connected in series circuit relation with said secondary winding and said tube, said shunt and said secondary winding being so proportioned and arranged relative to said condenser and said tube as to provide in the secondary circuit an oscillatory operating condition at said frequency in the neighborhood of series resonance thereby to ing characteristic, a transformer including a core having primary and secondary windings thereon respectively connected across said source and said tube andhaving a turn ratio such that the open circuit voltage of saidsecondary winding is sufficient to effectinitial breakdown of said tube, said transformer including a high reluctance shunt magnetically disposed between said windings for relaxing the coupling therebetwe'en upon the flow of current in said secondaryv winding, and ca-' pacity reactance means connected in series circuit relation with said secondary winding and said tube proportioned to establish upon initial breakdown of said tube an oscillatory condition of a series resonant nature, whereby the operating current flowing in said tube is built up by the resonant constants of the secondary series circuit and is limited by the maximum flux density of said core to an optimum value regardless of the negative impedance characteristics of said tube.

7 In an alternating current supply system, the combination with an alternating current source of predetermined voltage and frequency, of a gaseous discharge tube having a high initial breakdown voltage and a negative impedance operating characteristic, a transformer including primary and secondary windings respectively connected across said source and said tube and having a turn ratio such that the open circuit voltsaid tube proportioned to establish upon initial breakdown of said tube an oscillatory condition 01 a series resonant nature, whereby the operating current flowing in said tube by virtue of the resonant constants of the secondary series circuit substantially saturates the secondary section of said core and is limited to an optimum value regardess of the negative impedance characteristics 01 said tube, said resonant condition of said secondary circuit being effective to maintain said optimum current flow independently of fluctuations in the voltage of said source over a sub, stantial range.

8. In an alternating current supply system, the combination with an alternating current source of predetermined voltage and frequency, of a gaseous discharge tube having a high initial breakdown voltage and a negative impedance operating characteristic, a transformer including magnetic core means having primary and secondary windings disposed thereon and respectively connected across said source-and said tube and having a turn ratio such that the open circuit voltage of said secondary winding is suflicient to effect initial breakdown of said tube, said core means including a high reluctance shunt magnetically disposed between said windings for relaxing the coupling therebetween upon the flow of current in said secondary winding, said core means and said secondary winding being so proportioned that said secondary core portion operates at substantially maximum flux density upon the flow of a secondary current corresponding to optimum operation of said tube, and capacity reactance means connected in series circuit relation with said secondary winding and said tube, the impedance characteristics of said secondary winding, said condenser and said tube at said frequency being so related as to provide a substantially resonant circuit, whereby said optimum but limited current flow through said tube is obtained at substantially unity power factor.

9. In an alternating current supply system, the combination with an alternating current source oi predetermined voltage and frequency, of a gaseous discharge tube having a high initial breakdown voltage and a negative impedance operating characteristic, transformer means including magnetizable core means having primary and secondary windings thereon, said windings having a turn ratio such that the open circuit secondary voltage is suflicient to eiiect breakdown of said tube when said primary winding is connected to said source, and a condenser connected in series circuit relation with said tube and said secondary winding, said magnetizable core means including a high reluctance shunt magnetically disposed between said windings and effective upon the flow of current in said secondary winding to relax the coupling between said windings, said condenser having an impedance so proportioned relative to the impedance oi said secondary winding with a small current flowing therein at said frequency as to provide an oscillatory condition in the nature of series resonance, the impedance 0! said secondary winding varying upon an increasing flow of current so as tomore closely approach the impedance of said condenser until a stable series resonant condition is reached with amaximum current flow corresponding to optimum operation of said tube and to the maxi, mum flux density oi the secondary section of said core? thereby limiting said current flow regardless of said negative impedance characteristic of said tube. p

JOSEPH G. SOLA.

Images