US 3666986 A
A discharge lamp comprising an arc tube and an incandescible filament connected in series within an outer jacket. An integral four-diode bridge rectifier operates the lamp on rectified alternating current and the filament limits the current through the arc tube. The lamp operates reliably with a greater proportion of the line voltage applied across the arc tube than in conventional resistively ballasted lamps, resulting in higher efficiency. One or more diodes may be paralleled by a small capacitor to provide a voltage doubling effect to start the lamp.
Description (OCR text may contain errors)
United States Patent Lake et al.
[451 May 30,1972
 INTERNALLY RESISTIVELY BALLASTED DISCHARGE LAMP CONTAINING BRIDGE RECTIFIER  Inventors: William H. Lake, Novelty; Nicholas W.
Medendorp, Willowick, both of Ohio  Assignee: General Electric Company  Filed: July 15, 1970 [21 Appl. No.: 54,880
 US. Cl ..315/49, 313/198, 313/229,
315/205, 315/241, 315/330  Int. Cl. ..H0lj 61/56 I  Field of Search ..315/49, 58, 59, 200 R, 205,
 References Cited UNlTED STATES PATENTS 3,527,982 9/1970 Lake ..3l 5/200R 2,928,024 3/1960 Dawley ..3l5/205X 2,757,318 7/1956 Noeletal. ..3l5/20S Primary Examiner-Roy Lake Assistant Examiner-Siegfried H. Grimm AtmrneyEmest W. Legree, Henry P. Truesdell, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman  ABSTRACT A discharge lamp comprising an arc tube and an incandescible filament connected in series within an outer jacket. An integral four-diode bridge rectifier operates the lamp on rectified alternating current and the filament limits the current through the arc tube. The lamp operates reliably with a greater proportion of the line voltage applied across the arc tube than in conventional resistively ballasted lamps, resulting in higher efficiency. One or more diodes may be paralleled by a small capacitor to provide a voltage doubling effect to start the lamp.
12 Claims, 4 Drawing Figures Patented May 30, 1972 9, Sheets-Sheet 1 v w 5 n w Q mf n mm A m ww Wm N Patented May 30, 1972 3,666,986
2 Sheets-Sheet 2 Fig 3. Fig. 4.
f 33 E Y9 -39 lnvenTors:
WiLLiam H. Lake Nichotas W. Med ndofp DH Their- A t torneg INTERNALLY RESISTIVELY BALLASTED DISCHARGE LAMP CONTAINING BRIDGE RECTIFIER CROSS-REFERENCE TO RELATED APPLICATION Copending application, Ser. No. 757,180, filed July 31, 1968 by William H. Lake, entitled Discharge Lamp Ballasting and similarly assigned, now US. Pat. No. 3,527,982.
BACKGROUND OF THE INVENTION The invention relates to an improved low cost resistively ballasted high intensity metal vapor discharge lamp of the double envelope or jacketed type. It provides a bridge rectifier circuit as an integral part of the lamp which makes possible a higher ratio of arc voltage drop to overall lamp voltage drop for greater efficiency.
Resistively ballasted arc lamps comprise an arc tube and an incandescible ballast filament connected in series and mounted within an outer jacket which is either evacuated or filled with an inactive gas. Such lamps intended for operation on a 230 to 240 volt supply are designed so that the filament operates at a red glow after the arc tube has warmed up. They achieve an efiicacy of about 30 lumens per watt with the filament contributing a small'proportion of red light which improves the color rendition of the-lamp. While 230 volt convenience and lighting circuits are common in Europe, this is not the case in the United States. This fact has prevented the 230 volt resistively ballasted arc lamp from achieving any appreciable commercial scope in the US.
In resistively ballasted arc lamps intended for 115 to 120 volt circuits, the arc tube and ballast filament are connected in series and in addition the arc tube is provided with a two-terminal filamentary electrode at one end. The lamp also in- The filamentary electrode heats up whereupon the thermal switch opens; at the opening of the thermal switch the arc starts and the current is thereafter regulated by the ballast filament. If the lamp fails to start on the first opening of the thermal switch, the switch recycles until starting is achieved. The efficiency of this lamp is initially from 16 to 20 lumens per watt (depending upon size) and the maintenance is poor, the light output dropping to less than 50 percent of initial within 2,000 hours. The circuit arrangement and mode of operation are essentially similar to the well-known domestic 275 watt sunlamp used for skin tanning and sold under the designation RS 275. The very low efficiency and poor maintenance of this lamp, about equal to that of an incandescent lamp of the same wattage, has prevented it from achieving any substantial popularity.
In normal operation of electric lamps, it happens occasionally that the supply voltage is momentarily reduced, as when motors are started or because of overall poor regulation of the power system. A lamp may then cease to operate or drop out if the voltage applied to it falls below a critical value known as the drop-out voltage. Since high pressure metal vapor lamps require several minutes to cool down before they can be restarted, it is important to avoid lamp drop out. For filament ballasted arc lamps, a design criterion commonly used requires that the lamp shall continue to operate with an 18 percent temporary reduction of the nominal supply voltage. By way of example, on a 230 volt, 60 cycle A.C. supply, drop out voltage must not exceed 188 volts, and this limits the arc tube to one having an R.M.S. voltage drop not exceeding 135 volts. In a resistively ballasted lamp, lamp efficacy is proportional to the ratio of arc tube voltage drop to arc tube plus ballast filament voltage drop. Thus the need to avoid drop out sets a limit on efficacy. The object of the invention is to improve the efiicacy of resistively ballasted arc lamps.
SUMMARY OF THE INVENTION In an electric lamp operating on alternating current, there is a complete interruption of current at each reversal occurring twice per cycle. Before current flow can restart, the instantaneous voltage must rise sufficiently to effect two requirements: (1) establishment as cathode of the electrode which was anode during the preceding half cycle; (2) reestablishment of a minimum conductivity in the plasma. The voltage required to satisfy these conditions varies with the type of lamp and with the pressure and composition of the discharge medium. By operating alamp on DC, the first requirement is eliminated and the second is reduced, with the end result that the extinguishing voltage is appreciably reduced.
In accordance with our invention, advantage is taken of the foregoing by providing, integrally with a resistively ballasted arc lamp, a full wave bridge rectifier which converts the A.C. supply voltage to DC. and thereby reduces the extinguishing voltage. This in turn permits the use of a higher voltage arc tube and an increase in the ratio of voltage drop across the arc tube to voltage drop across thearc tube plus ballast filament resulting in increased efficacy. Preferably the bridge rectifier is mounted within the lamp base or within the outer jacket of a double envelope lamp. Lamp efficacy may be further increased by designing the arc tube specifically for DC. operation through optimization of the respective electrodes as anode and cathode.
In a preferred embodiment, at least one capacitor is connected in parallel with onediode of the bridge to provide a voltage doubling efl'ect for starting the lamp. The size of the capacitor through which voltage doubling is effected is determined by the need to ignite the discharge only, not to operate the arc tube. After ignition, the bridge rectifier operates the lamp on rectified current and the diodes must have currentcarrying capacity adequate for this burden. During operation, the need for appreciable voltage to assure reignition after current reversal is substantially eliminated because the current does not reverse and never drops absolutely to zero. This means that by proper choice of ballast filament and arc tube, the lamp can operate reliably with a greater proportion of the line voltage applied across the arc tube than in conventionally resistively ballasted arc lamps, resulting in substantially higher efficiency.
In another resistively ballasted lamp embodying the invention and intended for 230 volt mains, starting is easily effected without recourse to voltage doubling. In this lamp, a bridge rectifier alone is used to lower the drop out voltage and permit the use of an arc tube having a higher voltage drop for greater efficiency.
DESCRIPTION OF DRAWINGS In the drawings wherein like reference characters indicate corresponding elements in the several views:
FIG. 1 illustrates a high pressure metal vapor arc lamp with the base components vertically exploded and which embodies the invention in preferred form.
FIG. 2 illustrates schematically the circuit arrangement of the lamp of FIG. 1.
FIG. 3 illustrates schematically some variants in lamp circuits embodying the invention.
FIG. 4 gives the waveforms of lamp voltage obtained prior to starting with various circuit arrangements.
GENERAL DESCRIPTION The operation of a discharge lamp may be separated into the three phases of start-up, warm-up, and operation. The start-up phase refers to the initial conditions prevailing prior to actual starting of the lamp. The warm-up phase relates to the operating conditions for a short time interval, usually a few minutes, after the lamp has started during which vapor pressure in the arc tube builds up. The operating phase continues indefinitely after the arc has stabilized and the lamp wattage is relatively constant.
The function of the ballast in a discharge lamp system is to provide the electrical characteristics necessary to control the vide current limitation. Finally during operation, the ballast must provide total regulation of current and power.
In copending application, Ser. No. 757,180, filed July 31, 1968, by William H. Lake, entitled Discharge Lamp Ballasting, now U.S. Pat. No. 3,527,982, one of us has described a rectifiercapacitor bridge circuit comprising a bridge rectifier with a pair of capacitors connected in parallel with two of the diodes on the output side. In this circuit, the capacitors are used as voltage doubling devices which permit starting of the lamp but they are also used during the operating phase. The capacitors are chosen sufficiently high in value to maintain current flow and ionization in the lamp during the interval in each half cycle when line voltage falls below arc-sustaining voltage. By way of example, the capacitors in that lamp-circuit combination may range in value from to 100 microfarads for metal vapor lamps up to 400 watts in size and the efficacy may range from 30 to 50 lumens per watt. The system efficiency, namely the ratio of arc tube watts to overall input watts ranges from '75 to 90 percent. The combination may be described as a high capacitance, high efliciency voltage doubler resistance or VDR system.
The combination of the present invention in its preferred form may be described as a low capacitance, low efficiency VDR system. In this arrangement, the capacitances are used to supply current during the start-up phase only. The current required to ignite the discharge is but a small fraction of the current required to maintain the arc in operation. This means that the size of capacitance in the low efficiency VDR system need be but a small percentage of the size of capacitor required for the high efficiency VDR system. By way of example, the capacitances required are less than one microfarad and generally in the range of 0.01 to 0.5 microfarad for the common sizes of high intensity metal vapor discharge lamps up to 1,000 watts. The efficacy ranges from 25 to 35 lumens per watt. The lower efficiency of the present system arises from the fact that current limitation is effected entirely by resistance. The system efficiency then is essentially the ratio of arc voltage drop to overall lamp voltage drop consisting of arc voltage plus filament voltage. In the low capacitance, low efficiency VDR system, efficiencies from 50 to 70 percent are realized.
The four diodes that constitute the rectifier bridge may be grain of wheat size silicon rectifiers encased in vitreous envelopes and capable of withstanding temperatures of several hundred degrees centigrade. The capacitances may consist of compact ceramic capacitors using barium titanate as dielectric. By way of example, they may be small discs about onehalf inch in diameter and less than one-sixteenth inch thick and likewise capable of withstanding temperatures of several hundred degrees centigrade. All the components of the rectifier capacitor bridge may be mounted either within the outer jacket or within the mogul screw shell of the lamp. For lamps which are operated base up it is desirable to provide heat reflector discs in the neck of the lamp in order to limit the base temperature.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, a resistively ballasted high pressure mercury vapor lamp 1 embodying the invention comprises an outer vitreous envelope or jacket 2 of ovoid shape fabricated of soft glass. The neck 3 of the outer envelope is closed by the usual reentrant stem through which extend relatively stiff inlead wires 4,5. The inner arc tube 6 of quartz is provided at opposite ends with a pair of main discharge supporting electrodes 7,8 on ribbon type inleads pinch-sealed through the flattened ends of the tube. Each electrode comprises a double tungsten wire helix activated with an electronemitting mixture such as alkaline earth oxides or thorium oxide. An auxiliary startingelectrode 9 is provided at the upper or base end of the arc tube and is connected through the usual current limiting resistor 11 to inlead 4 by way of single side rod harness 12. The side rod is welded to inlead 4 and extends to an anchoring dimple 13 at the dome end of the jacket which is engaged by a springy clamp 14. The are tube is supported in the harness by clamping its flat ends between metal bands 15,16 which extend between side rod 12 and complementary rod end portions 17,18.
An incandescible ballasting filament 19 is mounted to extend from conductor 21 welded to side rod 12 near its midpoint to conductor 22 attached to the inlead of electrode 8. An insulated support wire 23 encircles the ballast filament near its mid-point to provide additional support. Side rod 12 serves as a conductor which connects main electrode 8 in series with ballasting filament 19 to inlead 4. The other main electrode 7 is connected directly to inlead 5. A pair of heatreflector discs are mounted in the neck of the outer envelope just below the stem and have a central aperture through which the inleads 4,5 extend. The lower disc 24 is welded to the top of the side rod 12 and the upper disc 25 is supported from the lower disc by means of a tab 26 on one side. These discs are necessary in the base-up lamp in order to reduce the temperature of the base and of the bridge components mounted within it. In a similar lamp intended for base-down operation, the heat-reflector discs may be omitted.
In the illustrated lamp, arc tube 6 contains a charge of mercury and an inert gas such as argon at a pressure below millimeters of mercury. Alternatively, the lamp may contain metal halides in addition to the mercury charge, for instance sodium iodide, thallium iodide, and indium iodide. Where the arc tube contains sodium iodide, the electron-emitting material used on the electrodes is thorium oxide.
The bridge rectifier comprises diodes D1 to D4 which are mounted in a-cluster on the underside of a fiber disc 27. The two capacitors C1,C2 are mounted on the top side of the disc. The disc is located between the upper end of the neck of the jacket and the inner shell 28 of the base. The inner shell is provided with 4 tabs 29 which have inwardly directed protuberances 30 engaging mating dimples 31 in the end of the neck. The inner shell is threaded and, the base 32 consisting of threaded outer shell 33, insulating glass web 34 and eyelet or center contact 35 is screwed down on the inner shell and locked in place by sheared-in tabs 36.
The diodes of the bridge rectifier are connected between the input junction points jl ,j2 and the output or conjugate junction points 3,} 4. Input point jl is connected by lead 37 to the center contact 35 of the base while input point 12 is connected by lead 38 to inner shell 28 which is engaged by outer shell 33 of the base. Conjugate point j3 is connected to inlead 4 while conjugate point j4 is connected to inlead 5. The diodes are connected for forward conduction toward conjugate point j3 and away from conjugate point j4. Capacitors Cl and C2 are connected in parallel with diodes D3 and D4, respectively.
When voltage is first applied, arc tube 6 prior to ionization appears as an open circuit. The rectifier capacitor bridge then operates as a conventional voltage doubler. On one half cycle, forward conduction through D1 charges up capacitor C1 with the polarity indicated to the peak E of the line voltage. On the next half cycle, forward conduction through D2 similarly charges up capacitor C2 with the polarity indicated to the peak E of the line voltage E. Thus capacitors C1 and C2 in series develop a voltage 2E across the conjugate junction points 3,14 making j3 positive and j4 negative. This effectively applies a voltage of 2 2 times line voltage, that is 325 volts in the case of a volt supply, between main electrode 7 and auxiliary electrode 9 of the arc tube. Such voltage resulting from the voltage doubling effect is sufficient to ionize the arc tube and start the discharge. The illustrated connections result in negative polarity at main electrode 7 and positive polarity at auxiliary electrode 9 and are preferred for easy starting of the lamp. After starting, diodes D1 to D4 operate in conventional fashion as a bridge rectifier to maintain the arc discharge on rectified alternating current.
FIG. 3 illustrates a resistively ballasted lamp embodying the invention and intended for 230 volt mains. A full wave bridge rectifier consisting of diodes D1 to D4 connected between input points j1, 2 and the conjugate output points j3,j4 is used to operate the lamp on rectified current. The bridge components may be mounted in a cluster within the base with points jl J2 connected to center contact 35 and inner shell 28 respectively, and points 13, 4 connected to inleads 5 and 4 respectively. Alternatively the four diodes of the bridge may be mounted within the outer jacket 2 of the lamp, preferably at the upper end about the stem tube and above the heat reflector discs where the temperature is lower. Since starting is not a problem with a 230 volt supply, no voltage doubling capacitors are provided. However the extinguishing voltage is considerably reduced permitting the use of a higher voltage are tube 6 whereby the ratio of arc tube voltage drop to arc tube plus ballast filament voltage drop is increased for greate efi'icacy.
The following table indicates the considerable improvement in efficacy obtained by providing a full wave bridge rectifier in a 230 volt resistively ballasted arc lamp.
Some high intensity metal vapor lamps are particularly dif- I ficult to start. For instance mercury metal halide lamps in general are more difficult to start than mercury vapor lamps of equivalent size or wattage. Also starting is more difficult at low temperatures. For lamps which are more difficult to start, an improved starting effect may be achieved by using only one capacitor in parallel with one of the diodes of the bridge. For instance, in the lamp of FIGS. 1 and 2, capacitor C2 may be removed, leaving only capacitor C1 connected in parallel with diode D3. When two capacitors are used in the bridge as shown in FIG. 2, charging of the capacitors begins during the first half cycle of the line voltage shown by curve 39 in FIG. 4, and thereafter the voltage applied across lamp terminals j3,j4 is a steady DC. of value 2E as shown by curve 40. When only one capacitor is used, the voltage across the lamp terminals varies cyclically from 0 to 2E as shown by curve 41. Thus the voltage doubling effect is present along with an alternating voltage which better utilizes the capacitive effects on the arc tube to initiate the discharge. A minor disadvantage of utilizing a single capacitor for voltage doubling effect is the possibility of damage to the conjugate diode D4 resulting from a transient voltage surge at a time when the lamp is hot from prior operation and unable to restart immediately. The likelihood of such a contingency is extremely small. In any case it can be circumvented by using high breakdown voltage rectifiers or avalanche protected diode rectifiers able to withstand such a transient. After starting, the lamp operates on rectified alternating current as shown by curve 42.
What we claim is new and desire to secure by Letters Patent of the United States is:
1. A dual envelope internally resistively ballasted arc discharge lamp comprising:
an outer vitreous jacket,
an inner arc tube having electrodes sealed therein and containing metal vapor, an incandescible filament proportioned to regulate the current flowing through said'arc tube, said arc tube and filament being mounted within said jacket, a base fastened to said acket having two terminals for connection to an A.C. supply,
a rectifier bridge in said lamp comprising four diodes disposed between two input points connected to said base terminals and two conjugate output points,
said are tube and filament being connected in series across said output points,
and said rectifier bridge having current carrying capacity adequate to sustain an are on rectified alternating current in said are tube.
2. A lamp as in claim 1 wherein said are tube includes an auxiliary starting electrode and the rectifier bridge connections make the main electrode next to said auxiliary electrode negative for easier starting.
3. A lamp as in claim 1 wherein said base is a screw base mounted on a neck at one end of said jacket and said rectifier bridge is located within said base.
4. A lamp as in claim 1 wherein the four diodes of said rectifier bridge are mounted in a cluster on a flat insulator in said base.
5. A lamp as in claim 1 wherein the four diodes of said rectifier bridge are mounted within a neck at one end of said jacket.
6. A dual envelope internally resistively ballasted arc discharge lamp comprising:
an outer vitreous jacket,
an inner arc tube having electrodes sealed therein and containing metal vapor,
an incandescible filament proportioned to regulate the current flowing through said are tube,
said are tube and filament being mounted within said jacket.
a base fastened to said jacket having two terminals for connection to an A.C. supply,
a rectifier bridge in said lamp comprising four diodes disposed between two input pointsconnected to said base terminals and two conjugate output points,
said are tube and filament being connected in series across said output points,
and at least one capacitor connected in parallel with one diode to provide a voltage doubling efiect for starting a discharge in said are tube,
said capacitor having capacitance providing sufficient current to ignite a discharge in said are tube but insufficient to sustain arc current therein,
and said rectifier bridge having current carrying capacity adequate to sustain an are on rectified alternating current in said arc tube.
7. A lamp as in claim 6 wherein said are tube includes an auxiliary starting electrode and the rectifier bridge connections make the main electrode next to said auxiliary electrode negative for easier starting.
8. A lamp as in claim 6 wherein the elements of the rectifier bridge are mounted within a neck at one end of said jacket.
9. A lamp as in claim 6 wherein the capacitance of said capacitor is less than 1 microfarad.
10. A lamp as in claim 6 in a rating up to 1,000 watts wherein the capacitance of said capacitor is between 0.01 and 0.05 microfarads.
11. A lamp as in claim 6 wherein said base is a screw base mounted on a neck at one end of said jacket and said rectifier bridge and capacitor are located within said base.
12. A lamp as in claim 11 wherein the four diodes of said rectifier bridge are mounted in a cluster on a flat insulator in said base along with said capacitor.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3666986 D d y 3 1 97 William H. Lake, et a1.
Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
.Please cancel the cover sheet and sheets I and 2 of the drawings and substitute the attached sheets therefor.
Signed and sealed this 29th day of August 1972.
EDWARD M. FLETCHER,JR.
ROBERT GOTTSCHALK' Attesting Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC 60376-P69 i U.S, GOVERNMENT PRINTING OFFICE: 1989 0-366-334