US3250953A

US3250953A - Power supply for arc-lamp including automatic starting circuit

Info

Publication number: US3250953A
Application number: US208039A
Authority: US
Inventors: Charles E Everest
Original assignee: Consolidated Electrodynamics Corp
Current assignee: Consolidated Electrodynamics Corp; IMO Industries Inc
Priority date: 1962-07-06
Filing date: 1962-07-06
Publication date: 1966-05-10
Anticipated expiration: 1983-05-10

Description

May 10, 1966 c. E. EVEREST 3,250,953

POWER SUPPLY FOR ARC-LAMP INCLUDING AUTOMATIC STARTING CIRCUIT Filed July 6, 1962 2 Sheets-Sheet 1 LM/i/ 1 NVEN TOR. Czar/ 155 A. 0mm)" May 10, 1966 C. E. EVEREST POWER SUPPLY FOR ARC-LAMP INCLUDING AUTOMATIC STARTING CIRCUIT Filed July 6, 1962 2 Sheets-Sheet 2 g 11 L /4'0 1F .7 Z

536 4/ a? 1 55 a: m

i d /4 /4 /5 5 G if 42 N w 25; Z 1

J an /7 1 544 INVENTOR. CM a [s5 [l/[AA'57' 3,250,953 POWER SUPPLY FOR ARC-LAMP INCLUDING AUTOMATIC STARTING CIRCUIT Charles E. Everest, Sierra Madre, Calif., assignor to Consolidated Electrodynamics Corporation, Pasadena,

Calif., a corporation of California Filed July 6, 1962, Ser. No. 208,039 10 Claims. (Cl. 315200) This invention relates to power supplies for are lamps and more particularly to a power supply for a compactarc lamp incorporating an automatic lamp starting circuit.

It is well known that arc lamps produce illumination 'as a result of the production of an electrical discharge between a pair of electrodes. Arc lamps are available which produce illumination in various portions of the spectrum in accordance with the gaseous atmosphere and the gas pressure in which the electrical discharge is produced. Examples of a high power are lamp productive of high light intensities in the visible spectrum are the common carbon arc and mercury vapor lamps that have been employed for street lighting purposes. Arc lamps have also been developed that are small and compact that produce extremely high brightness in the ultraviolet, visible, and infrared regions of the spectrum for special purposes such as microphotography, spectrophotography, direct wire oscillography, and the like. Lamps of this type may employ xenon or mercury vapor enclosed in an envelope at relatively high pressures. The xenon or mercury vapor arc lamps have found extensive use in present day recording oscillographs and are known in the art as compact-arc lamps.

As in any are lamp, the compact-arc lamp requires that the electrical discharge be initiated between the electrodes and then the discharge sustained in order to produce the desired illumination. In the compact-arc lamp the starting of the lamp or the initiation of the electrical discharge usually requires the momentary application of a very high voltage pulse in the radio or microwave frequency range. For example, a xenon compact-arc lamp may require 10 watts of power on the order of 15,000 to 30,000 volts in the 1 to '10 megacycle range. Since the energization of a compact-arc lamp is sustained in terms of relatively low direct current voltages, it will be noted that the requirements for s-tarting'and maintaining the lamp energized are radically different. Accordingly, in many applications and, in particular the oscillographic applications utilizing the compact-arc lamp, separate circuits are utilized for starting the lamp and for maintaining itenergized. It is also characteristic of the starting circuits that they include relatively complex transistor and relay circuits for generating a starting pulse and transferring the starting pulse to the arc lamp and then further switching means to transfer the lamp from the switching circuit to the power or energizing circuit. This has involved a large number of electrical components that have had a limited life and are sensitive to high voltages and the like. These prior art starting circuits furthermore have not been self-starting and generally require that a starting button be actuated in order to produce the starting pulse after the power is applied to the lamp. From the standpoint of the power excitation circuit, the manufacturers specifications for operating the compact-arc lamps over their rated life require that the voltage applied thereto be within certain limits. To reduce the number of components and expense required for this purpose, some oscillographs employing compact-arc lamps have utilized a manual means for regulating the voltage to transfer this function to the operator rather than incorporating regulating means into the electrical power circuitry.

United States Patent The present invention provides an improved, simple, small, and relatively inexpensive power supply circuit for are lamps that incorporates an automatic lamp starting circuit that causes the lamp to be rapidly started. The power supply of the present invention includes a minimum of highly reliable electrical components-employs no relays, transistors, moving parts, or the like that have a limited life-and which power supply automatically adjusts itself to the aging of the lamp. The automatic starting circuit is incorporated into the power transformer for the lamp and which power transformer is a constant voltage or regulating transformer that automatically produces voltage regulation on the order of il% of the lamp power. The power supply circuit arrangement is such that the initiation of the electrical discharge in the arc lamp is not only automatically started, without resorting to any starting buttons, upon the application of power to the supply circuit but is also advantageously defined whereby the starting circuits and the lamp energizing circuits 'are essentially independently and alternately energized and de-energized in the correct time sequence. Furthermore, upon the loss of power or a sudden drop in power line voltage below the sustaining voltage of the arc lamp causing it'to become de-energized, the starting and energization cycle will be quickly repeated whereby the lamp will be automatically ignited within 17 milliseconds.

From a structural standpoint the invention comprises a power regulating transformer having a magnetic shunt between the primary and secondary windings for defining a high leakage reactance and which leakage reactance is defined in accordance with the operating characteristics of the arc lamp to act as the lamp ballast impedance. The power transformer primary winding includes a circuit adapted to resonate at the power frequency applied thereto and in combination with the saturable core develops a substantially constant voltage at the secondary winding means. The secondary winding means include a plurality of secondary windings, one of which is included in the automatic starting circuit While the other is included in the energization circuit for the arc lamp. The automatic starting circuit is adapted for momentarily generating a high frequency, high voltage starting pulse in response to the energy in its associated secondary winding and proportioned to start the arc lamp. This starting circuit includes a pair of spaced electrodes for producing the starting pulse by means of an electrical discharge therebetween and means for coupling the starting pulse to the arc lamp through the energizing circuit. The lamp energizing circuit is arranged with the other secondary winding and includes rectifying-filter means for producing the direct current potential for maintaining the lamp energized. A temporary storage device incorporated in the rectifying-filter means is arranged to temporarily store the energy received from the primary winding whereby it is effective to unload this secondary winding or block the transfer of energy thereto and thereby causethe transformer energy to be essentially coupled across the secondary winding for the starting circuit leading to the production of the electrical discharge between the spaced electrodes in the starting circuit. Upon the production of the electrical discharge in the starting circuit, the resulting starting pulse is immediately coupled to the arc lamp to initiate the electrical discharge for starting the lamp.- Substantially simultaneously with the energization of the lamp, the temporary storage device is discharged to a voltage level where it unblocks the associated secondary winding and once again is responsive to the transformer energy to allow the resulting rectified current to be applied to the arc lamp for maintaining it continuously energized. With the application of the energy of the primary winding to the energizing circuit,

the potential developed at the secondary winding for the startingycircuit is maintained at a level to prevent a further electrical discharge in the starting circuit and, therefore, essentially all of the power from the transformer is transferred to the energizing circuit to thereby maintain the lamp energized.

These and other features of the present invention may be more fully appreciated when considered in the light of the following specification and drawings, in which:

FIG. 1 is a schematic circuit representation of the power supply incorporating the automatic starting circuit embodying the invention;

FIG. 2 is a diagrammatic representation of the mag netic core configuration for the power transformer of FIG. 1;

FIG. 3 is a schematic illustration of another embodiment of the power supply circuit of FIG. 1; and

FIG. 4 is a diagrammatic representation of the magnetic core configuration for the power transformer as utilized in the circuit of FIG. 3.

Now referring to the drawings, the invention will be described as the power supply circuit may be employed with a compact-mercury arc lamp, although it should be understood that the invention could be used with other types of arc lamps.

The power circuit 10, shown in FIG. .1 comprises a power transformer 11 having a plurality of

secondary windings

12 and 13. The secondary winding 12 is included in an automatic lamp starting circuit, while the secondary winding 13 is included in a lamp power or energizing circuit. A

The power transformer 11 is further characterized as having a high leakage reactance to function as the ballast for the arc lamp 14 shown in circuit relationship with the secondary winding 13. The leakage reactance for the power transformer 11 is defined through the provision of a magnetic shunt arranged between the primary and secondary windings therefor, as will be explained more fully immediately hereinafter. In addition, the power transformer 11 includes a circuit in combination with the primary windings that is resonant to the power frequency applied to the primary winding for regulating the supply voltage within il% for supply voltage changes of 110% or more and, therefore, produces an essentially constant voltage output.

The power transformer 11 is shown as a ferromagnetic transformer having a center tapped primary winding 15. The primary winding 15 is connected at its center tap to an inductor 16 connected in series circuit therewith. The inductor 16, as represented in FIG. 1, has an iron core 16 including an air gap G arranged in the flux path of the winding therefor. The air gap G is represented in FIG. 1 as a pair of series of spaced horizontal lines arranged on opposite sides of the transformer core and identified by the reference letter 6;. The primary winding 15 is connected in parallel circuit relationship with a resonating capacitor 17 coupled between the opposite ends of the winding 15. The capacitor 17 is defined to resonate with the winding 15 at the power frequency applied to the primary winding from a suitable source. In general, the power transformer will be applied to a commercial source of alternating current and, therefore, the alternating current will be on the order of 60 cycles and 117 volts. It should therefore be noted that the parameters of the primary winding 15 and the capacitor 17 are defined in terms of this commercial 60 cycle source as Well as the other components to be described hereinafter. The primary' winding 15 is also shown arranged with an air gap G for controllably defining the high leakage reactance of the power transformer 11 or controlling the reluctance of the magnetic shunt between the primary winding 15 and the

secondary windings

12 and 13.

Now referring to FIG. 2, the physical configuration of the power transformer 11 along with the inductor 16 will be more closely examined. It should be noted, at the outset, that the inductor 16 and the power transformer 11 are shown as separate elements for the purposes of this invention but the inductor 16 may readily be incorporated into the magnetic structure for the power transformer 11 to provide a unitary assembly. The inductor 16 may be constructed in terms of conventional E-I core laminations with the winding 16 arranged in the central portion of the E lamination, as shown, whereby a closed magnetic flux path is defined and the air gap G is defined in this flux path between the E and I laminations at the outer legs and is proportioned to cause the inductor to exhibit a linear reactance. The one output terminal from the inductor 16 is connected to the power source while the other terminal is connected to the center tap of the primary winding 15 for the power transformer 11, as described hereinafter.

The power transformer 11 is shown as comprising a rectangular core that may consist of a pair of E laminations associated with an I lamination defining a closed flux path. The pair of

E laminations

20 and 21 are arranged back to back with the I lamination 22, abutting the E lamination 20 for closing the magnetic flux path. The primary winding 15 is arranged on the central arm of the lamination 20, while the

secondary windings

12 and 13 are tightly coupled to the central arm of the lamination 21 whereby voltages induced therein' from one to the other are constrained to be very nearly their turns ratio.

The primary winding 15 and the

secondary windings

12 and 13 are spaced apart in accordance with this construction rather than being tightly coupled to one another as in conventional transformer design for minimizing the leakage reactance. It will be noted that the portion of the magnetic core identified by the reference numeral 20 functions as a magnetic shunt for the flux provided by the primary winding 15 and, therefore, since this flux does not couple the

secondary windings

12 and 13, may be termed leakage flux. This magnetic shunt is defined in accordance with thev lamp characteristic whereby the resulting leakage reactance may function as the ballast impedance for the arc lamp 14. To this end, this leakage reactance is controlled in accordance with the necessary operating characteristics of the arc lamp 14 by defining the length of the air gaps G shown in the shunt arm 2t) on opposite sides of the secondary winding 15. Since a compact-arc lamp is generally considered to be a constant power device, this leakage reactance voltage and current characteristic should be defined toward this end.

Now returning to FIG. 1 the circuits associated with the secondary windings 12 and '13 will be more closely examined. The circuit associated with the secondary winding 12 is the automatic star-ting circuit and includes means for generating the high voltage, high frequency starting pulse for the arc lamp 14. To this end, the starting pulse generating means is shown as a pair of spaced

electrodes

25 and 26 mounted on an insulating supporting member 27, shown as a U-shaped member. The

electrodes

25 and 26 may be conveniently and inexpensively constructed of a pair of conventional screws threaded into the insulating member 27 and spaced by an air gap 28 whereby the air gap 28 ends may be readily adjusted. As shown, the electrode 26 is connected to a point of reference potential or ground while the electrode 25 is connected to a starting pulse coupling element shown as a pulse transformer 31. The primary winding 32 of the pulse transformer 31 is connected between the electrode 25 and one terminal of the secondary winding 12 and which secondary winding has its other terminal connected to ground or in common with the electrode 26.

The other secondary winding 13 .for the power transformer 1 1 is shown connected to a rectifier-filter combination for producing the direct current potential necessary for powering the :arc lamp '14. The circuit elements comprising the rectifier-filtercombinaton are arranged within the box shown in dotted outline and comprise a conventional full-wave diode rectifying circuit shown in terms of the semi-conductor diode rectifiers 33 and 34 connected in rectifying relationship to the opposite terminals of the secondary winding 13. The filtering element associated with the rectifier is shown in terms of a single zfiltering capacitor 35 connected in common with the cathodes of the diodes 33 and 34 and ground and, accordingly, is common with the grounded center tap for the secondary winding 13. The energizing circuit is completed by means of a circuit connection to the secondary winding 36 for the pulse transformer 31, which is connected to the anode 14 of the arc lamp 14 and which arc lamp has its cathode electrode 14 connected to ground. The circuit is further represented as including a resistance element 37 connected in series circuit relationship between the capacitor 35 and the secondary winding 36 of the pulse transformer 31 and includesa shorting switch 38 arranged in parallel circuit relationship therewith. The switch 38 is normally closed and, therefore, the resistor 37 can be disregarded for the purposes of the present discussion.

With the above structure in mind, an examination of the components of the circuit of FIG. 1 will make the circuit operation more evident. First examining the power transformer 11 and, in particular, the primary winding means therefor, it will be noted that the arrangement is such that the combination of the resonant circuit comprising the winding and the capacitor 17 and the magnetic characteristics of its associated magnetic core is such that the. portion of the magnetic core associated with the primary winding 15 is driven and operated in a saturated condition. Therefore, when the primary circuit is operated in saturation a nearly constant rate of change of [flux or constant dqs/dt is established in the portion of the core associated with the

secondary windings

12 and 13. This constant rate of change of flux in the portion of the core associated with the secondary circuits occurs during each of the half cycles of the. alternating current input signal. It will be appreciated that with a constant rate of change of the flux cutting the

secondary windings

12 and 13 that a nearly square wave output is derived from these windings and an essentially constant amplitude voltage is derived therefrom. The leakage flux that passes through the core portion has been defined by means of high reluctance elements for the air gaps G to be consistent with the open circuit voltage and short circuit currents of the arc lamp. In addition, the resulting impedance corresponding to the leakage flux is proportioned to function as a ballast impedance to place the load on the arc lamp 14 at the correct voltage and current for sustaining the energization of the lamp over its normal operating range. Specifically, the resulting load characteristic for the lamp should be adjusted by means of the leakage reactance to allow the voltage and the cur-rent applied to the arc lamp to maintain the lamp at its rated constant power characteristic.

Now referring to the operation of the starting circuit for the lamp and which starting circuit is associated with the secondary winding 12, it will be seen that normally no current is drawn in this circuit due to the air gap 28 defined between the electrodes and 26 for generating the starting pulse. Accordingly, the voltage required to produce an electrical discharge between the

electrodes

25 and 26 may be considered as the critical voltage required for energizing the starting circuit. This critical voltage necessarily must be defined and proportioned in terms of the starting pulse required for the particular are lamp 14 utilized in the circuit. In addition, the power circuit or the low voltage circuit may be considered to have a critical voltage which is the open circuit direct current voltage presented to the lamp upon starting. In a typical compact-mercury arc, 10 watt lamp this open circuit voltage may be on the order of 55 volts and the open circuit voltage must be limited to this value. In

practice, this critical low voltage 'value may be obtained by merely adjusting the length of the air gap 28 between the

electrodes

25 and 26 until an electrical discharge is produced. To this end, the voltage required to cause an electrical discharge between these electrodes or the voltage V may be defined by the following formula:

wherein N and N refer to the number of turns in the

secondary windings

12 and 13; (since only one-half of the secondary winding 13 is utilized during each half cycle, the formula takes this int-o consideration by the constant 2.) an E is the rated open circuit voltage for the arc lamp.

It should be recognized that the relative setting of the

electrodes

25 and 26 may be readily attained by moving one electrode towards the other while observing the arc lamp and noting when the lamp is ignited. This, then, sets the pulse generating means to the correct spacing for breaking down the air to generate the starting pulse and also determines the open circuit voltage applied to the lamp 14. It should be recognized that an electrical discharge produced between a pair of electrodes is rich in high frequency components and which components are in the range required for triggering a compact-arc lamp. The voltage required for breaking down the gap and producing the discharge between the

electrodes

25 and 26 is derived from the secondary winding 12 of the power transformer 11 and coupled to the lamp 14 by means of the pulse transformer 31. If the high voltage pulse derived from the secondary winding 12 is not sufficient, it may be increased by constructing the pulse transformer 13 as a step-up transformer whereby the winding turns are proportioned to step-up the discharge voltage to the correct required starting voltage.

With the above considerations in mind, the operation of the automatic starting circuit along with the automatic switching of the energy from the power transformer primary between the

windings

12 and 13 will be examined in greater detail. When the power is first applied to the primary winding 15 of the power transformer 11, the loading effect of the filter capacitor 35 on the secondary winding 13, plus the current limiting elfect of the leakage inductance due to the air gaps G combine to keep the voltages on the tightly coupled

secondaries

12 and 13 low for a few cycles until the capacitor 35 charges up. As the capacitor 35 approaches the open circuit voltage for the lamp 14, or 55 volts, the voltage between the electrodes 25. and 26 approaches the break down potential. As the first peak of the input wave exceeds the breakdown voltage for the

electrodes

25 and 26 it results in an electrical discharge therebetween and the impedance between these electrodes instantaneously drops to a very low value, as is characteristic of a gaseous discharge. Under these conditions the secondary winding 12 is effectively shorted out and its voltage drops to a very low value. Due to the tight coupling between the

secondary windings

12 and 13 the peak voltage across the secondary winding 13 follows the voltage across the secondary winding 12 to its low value. Therefore, the potential stored by the capacitor 35, or 55 volts, is greater than this low value and is therefore effective to back bias the diodes 33 and 34 whereby the secondary winding 13 is completely unloaded or is effectively in an open circuit condition. This, then, transfers the entire input energy from the primary winding 15 to the secondary winding 12, and, therefore, the entire output of the power supply is utilized to drive the electrical discharge between the

electrodes

25 and 26 and consequently the primary winding 32 of the pulse transformer 31. With this circuit arrangement, this high frequency starting power is approximately an order of magnitude greater than that needed to start the commercially available compact-mercury vapor arc lamps under normal conditions and consequently the circuit of the present invention is capable of starting even aged lamps in one-half cycle of the power line voltage.

vAs was mentioned hereinabove, the circuit components are proportioned and defined in terms of a power frequency of 60 cycles and, therefore, the high radio or megacycle frequencies generated by the electrical discharge between the

electrodes

25 and 26 are presented with very low irnpedances at these frequencies whereby the high frequency components in the electrical discharge are effectively placed directly across the primary winding 32. In addition, the capacitor 35 and the secondary winding 36 present a low impedance to these high frequency starting pulses whereby the starting pulse is applied directly between the anode and cathode of the arc lamp to initiate the energization thereof.

With the initiation of current flowing between the electrodes of the arc lamp the charge stored on the capacitor 35 is discharged through the lamp 14 whereby it is reduced to a level that unblocks the diodes 33 and 34 and allows them to conduct. The charge stored on the capacitor 35 rapidly drops to this unblocking potential, in this instance apporximately 50 volts. With the conduction of the diodes 33 and 34, the power from the primary winding 15 is switched back to the secondary winding 13 and the starting circuit is essentially switched off since the voltage necessary for producing another electrical discharge between the

electrodes

25 and 26 cannot be reached with the winding 13 unblocked. Therefore, the entire power from the primary winding 15 is coupled to the secondary winding 13. After the lamp 14 begins to conduct current the voltage across the capacitor 35 and, therefore, across the lamp 14 drops automatically to a value which is approximately one-half the open circuit value for the lamp and which open circuit value is sufiicient. to sustain the current flow through the lamp and maintain it ener-- gized. The lamp, therefore, will remain energized under these circuit conditions as long as the power is maintained across the primary winding 15.

It should also be noted that an important aspect of the present power supply circuit is that after the lamp 14 is energized, if the power line voltage should suddenly drop below the sustaining voltage for the lamp andthe lamp becomes extinguished, the above automatic starting and switching cycle will be rapidly and automatically initiated upon the return of the power voltage to its normal value. The lamp 14 would then be automatically ignited within 17 milliseconds of the application of the normal power to the circuit. This automatic starting feature is a very important feature, particularly when the invention is utilized in conjunction with arc lamps for recording oscillographs wherein a one second loss of data could be very costly.

The above circuit description is typical for a mercury lamp as utilized in recording oscillographs. It is well known that xenon compact-arc lamps'are employed in lieu thereof. The substitution of a xenon lamp utilized with the present invention merely requires the opening of the switch 38 to place the resistor 37 in circuit with the power circuit to the lamp. Since the xenon arc lamp is typical of the lower power lamps, the resistor 37 is merely proportioned to be compatible with the rated lamp power. The circuit operation, then, is identical to that described hereinabove.

Now referring to FIGS. 3 and 4 another embodiment of the power supply circuit of the present invention will be described. In general, the circuit shown in FIG. 3 is essentially the same as the circuit of FIG. '1 in operation but has been modified to maximize the circuit operation.

As was indicated hereinabove, compact-arc lamps generally have a constant power characteristic and, therefore, the ballast impedance must have a voltage versus current characteristic to maintain the power absorbed by the lamp substantially constant over its operating range. Therefore, the voltage versus current characteristic curve is in the form of .a hyperbQla. To achieve this hyperbolic characteristic the reactive elements of the power transformer 11 have been modified whereby the primary winding 15 is defined in terms of a pair of parallel inductors, shown in the drawings as the

inductors

15A and 15B and coacting with a pair of

parallel inductors

13A and 13B. As will be noted, each of the

inductors

15A and 15B are shown as having a pair of winding portions A-1 and A-2 and B1 and B-2. The portions A-1 and B-1 are connected in parallel circuit relationship with the series inductor 16. The other portions A-2 and B2 are connected in parallel and, in turn, this same parallel combination is connected in series with the resonating capacitor 17. This latter combination defines the circuit that is resonant to the power line frequency. i

A further characteristic of this modified power transformer 11 is that the combination of

inductors

13A and 13B are each defined to have a different impedance characteristic whereby the combination of these impedance characteristics approaches the desired hyperbolic characteristic, at least over the normal operating range of the lamp and allows the lamp to function as a constant power device. These center tapped

windings

13A and 13B have their center taps connected to ground, and each Winding has individual full

wave rectifying elements

33A and 34A and 33B and 34B individually connected thereto. These rectifying elements are operated in parallel circuit fashion and are connected in common to the power end of the filter capacitor 35.

The power circuit proper for the lamp 14 has also been modified whereby an additional filtering element is utilized along with the filtering capacitor 35 and which filtering element is shown as an inductor 41 connected in series circuit with the output of the rectifiers 33 and 34 and the secondary winding 36 for the pulse transformer 31. In addition, to aid the coupling of the starting pulse from the secondary winding 36 to the lamp 14, additional capacitors shown as the parallel combination of the capacitors 42 and 43 are coupled to the opposite terminal of the secondary winding 36 from the arc lamp 14 and in parallel circuit relationship therewith as shown. To this end, the filter capacitor 35 may be onthe order of 2500 microfarads while the capacitors 42 and 43 may be relatively small and on the order of 10 and .005 microfarads respectively. This latter pair of capacitors, then, reduce the impedance to the starting pulse and aid in coupling the starting pulse to the lamp 14.

The magnetic configuration of the modified power transformer 11 is shown in FIG. 4 with the corresponding windings of FIG. 3 identified by identical reference numerals. It will be seen that the power transformer comprises a pair of rectangular magnetic core elements having three legs with the central leg in each instance defining the magnetic shunt and having an air gap G therein. As in the previous embodiment, the central leg functions as the magnetic shunt whereby a substantial portion of the flux from the primary winding 15 is not coupled to the

secondary windings

12 and 13 to define the desired leakage reactance for lamp ballast purposes.

In addition, the starting circuit, including the secondary winding 12, has been modified through the inclusion of a, resonating capacitor 40 connected in series circuit relationship between the secondary winding 12 and the primary winding 32 for the pulse transformer 31. The capacitor 40 is proportioned relative to the inductance of the primary winding 32 to resonate at the particular radio or microwave frequency which is necessary for starting the lamp 14 and preferably is physically located adjacent the primary winding 32 to maximize the transfer of the starting pulse. It will be recalled that a wide range of frequencies are generated due to the electrical discharge beween the pair of

electrodes

25 and 26 and, therefore, this combination of reactances tunes the starting circuit to only the desired radio or microwave frequencies whereby only these frequencies are essentially coupled to the arc lamp 14 and, therefore, the transfer of energy at these frequencies is further maximized.

It should now be evident that the present invention provides an improved, simple, and inexpensive power supply that incorporates an automatic lamp starting circuit therein.

What is claimed is:

1. A power supply for an arc lamp comprising a power transformer having a ferromagnetic saturable core including a magnetic shunt with a primary winding and at least a pair of secondary windings megnetically coupled thereto on opposite sides of the magnetic shunt, said transformer including means for producing asubstantially constant voltage in the secondary windings, first circuit means connected to one of the secondary windings and being responsive to energization of the primary winding for generating an arc lamp starting pulse, and second circuit means connected to the other secondary winding for supplying an arc lamp after it is started, means included in the first circuit means coupled with means included in the second circuit means for delivering the starting pulse to the lamp supplying circuit, said second circuit means including temporary storage means responsive to energization of the primary winding for storing a preselected amount of energy therein to momentarily place said other secondary winding in an open circuit condition to transfer the input energy to said one secondary winding causing the starting pulse to be generated and then releasing the stored energy and transferring the input energy to said other secondary winding for continuously supplying an arc lamp.

2. A power supply as defined in claim 1 wherein said means for producing a substantially constant voltage comprises a ferroresonant circuit defined with the saturable core.

3. A power supply as defined in claim 2 wherein at least a portion of the primary winding is included in a circuit resonant to a power frequency to define the ferroresonant circuit.

4. A power supply as defined in claim 1 wherein said power transformer is further characterized by an excessive leakage reactance to function as a lamp ballast.

5. A power supply as defined in claim 1 wherein said second circuit means includes rectifiers connected between the other secondary winding and the temporary storage device whereby the energy stored in said device is effective to block the conduction of the rectifiers for transferring the primary winding energy to said first circuit means for generating the starting pulse.

6. A power supply as defined in claim 1 wherein said first circuit means includes a pair of spaced electrodes adapted to generate an arc lamp starting pulse and Wherein said means coupling the first and second circuit means comprises a pulse transformer.

7. A power supply as defined in claim 1 wherein the power transformer has a saturable magnetic core defined with at least three legs and a primary winding and a plurality of secondary windings magnetically coupled thereto, said primary winding being coupled to one of winding by the third leg whereby the third leg acts as a magnetic shunt for providing a fiux leakage path and thereby a leakage reactance, the leakage reactance being defined to function as a lamp ballast impedance to cause the lamp to operate as a constant power device.

8. A power supply circuit for an arc lamp as defined in claim 7 wherein the power transformer comprises a pair of saturable ferromagnetic cores for defining a pair of inductors comprising the primary windings of said power transformer, said pair of inductors having diiferent impedance characteristics defined to cause the combination of the impedance values to approach a hyperbolic characteristic to allow a lamp to function as a constant power device.

9. A power supply as defined in claim 1 wherein said temporary storage means comprises a capacitor.

10. A power supply circuit for an arc lamp comprising a power transformer having a saturable magnetic core defined with at least three legs and a primary winding and a plurality of secondary windings magnetically coupled thereto, said primary winding being coupled to one of the legs and said secondary windings being coupled to another of said legs and being spaced from the primary winding by the third leg whereby the third leg acts as a magnetic shunt defined for providing a flux leakage path and thereby a leakage reactance, the third leg and thereby the leakage reactance being defined to function as a lamp ballast impedance to cause the lamp to operate as a constant power device, a capacitor electrically connected to the primary winding to define a ferroresonant circuit therewith to cause a constant voltage to be generated in the secondary windings, a pair of spaced electrodes electrically connected in circuit relationship with one of the secondary windings to be energized therefrom, the electrodes being spaced a preselected distance for generating a lamp starting pulse, a pulse transformer having a primary winding electrically connected in circuit with said one secondary winding, and a capacitor electrically connected to the other secondary winding to be energized therefrom, said other secondary winding being effective to power a lamp after it is started, the secondary winding of the pulse transformer being connected to said other secondary winding and adapted to be connected to a lamp to be energized.

References Cited by the Examiner UNITED STATES PATENTS 2,509,188 5/ 1950 Feinberg. 2,664,541 12/ 1953 Henderson. 2,757,318 7/ 1956 Noel. 2,777,973 1/1957 Steele 315173 2,825,005 2/1958 Bird 315-289 3,036,240 5/ 1962 Scott 315289 JOHN W. HUCKERT, Primary Examiner.

J. D. KALLAM, Assistant Examiner.

Claims

1. A POWER SUPPLY FOR AN ARC LAMP COMPRISING A POWER TRANSFORMER HAVING A FERROMAGNETIC SATURABLE CORE INCLUDING A MAGNETIC SHUNT WITH A PRIMARY WINDING AND AT LEAST A PAIR OF SECOND WINDINGS MEGNETICALLY COUPLED THERETO AN OPPOSITE SIDES OF THE MAGNETIC SHUNT, SAID TRANSFORMER INCLUDING MEANS FOR PRODUCING A SUBSTANTIALLY CONSTANT VOLTAGE IN THE SECONDARY WINDINGS, FIRST CIRCUIT MEANS CONNECTED TO ONE OF THE SECONDARY WINDINGS AND BEING RESPONSIVE TO ENERGIZATION OF THE PRIMARY WINDING FOR GENERATING AN ARC LAMP STARTING PULSE, AND SECOND CIRCUIT MEANS CONNECTED TO THE OTHER SECONDARY WINDING FOR SUPPLYING AN ARC LAMP AFTER IT IS STARTED, MEANS INCLUDED IN THE FIRST CIRCUIT MEANS COUPLED WITH MEANS INCLUDED IN THE SECOND CIRCUIT MEANS FOR DELIVERING THE