US 3771018 A
A self-ballasted discharge lamp comprising an arc tube and an incandescible filament connected in series within an outer jacket includes an integral full wave bridge rectifier. The bridge comprises four diodes and optionally one or two ceramic capacitors which are assembled into a screw base of standard external dimensions. Two diodes are heat sunk directly to the center contact of the base while the other two diodes are heat sunk directly to the base shell. This configuration provides excellent heat dissipation characteristics, mechanical strength and simple assembly.
Claims available in
Description (OCR text may contain errors)
United States Patent Medendorpvetal. Nov. 6, 1973 54] DISCHARGE LAMP CONTAINING BRIDGE 3,148,305 9/1964 Pearson 1. 315m x RECTIFIER 3,372,302 3/1968 Fasola 315/200 R X  Inventors: Nicholas W. Medendorp, Willowick; P E R k William H. Lake, Novelty, both of '"f La 6 Ohio Asslstant Exammer-Lawrence .1. Dahl Attorney-Ernest W. Legree et al.  Assignee: General Electric Company,
, Schenectady, NY. I d  ABSTRACT 22 F' M 5 1972 l 1 l e ay A self-ballasted discharge lamp comprising an arc tube  App]. No.: 250,646 and an incandescible filament connected in series within an outer jacket includes an integral full wave 7  CI 315/200 R 315/51 31 5/71 bridge rectifier. The bridge comprises four diodes and  Int Cl g 37/00 optionally one or two ceramic capacitors which are as-  Field I51 71 179 sembled into a screw base of standard external dimen- 3 sions. Two diodes are heat sunk directly to the center I contact of the base while the other two diodes are heat  References Cited sunk directly to the base shell. This configuration provides excellent heat dissipation characteristics, me- UNITED STATES PATENTS chanical strength and simple assembly. 3,527,982 7/1968 Lake 315/200 R 2,928,024 3/1960 Dawley 315/51 9 Claims, 7 Drawing Figures r M ,4 1 P4 "5 \\\i F A,
53 g, 40 \w' "t 5/ l 52 I 1 l g :s; I. s. 4/ l f I l l 45 1 '46 PATENTED RUY 6 I975 SHEET 10F 2 PATENTEDunv sum 377L018 SHEETEGF 2 DISCHARGE LAMP CONTAINING BRIDGE RECTIFIER I BACKGROUND OF THE INVENTION tion, we have disclosed a resistivelyballasted arc lamp 1 which includes an integral full-wavebridge rectifier. The bridge rectifier converts the A-.C. supply voltage to D.C. and thereby reduces the extinguishing-voltage since there is no longer the need at every half cycleto establish as cathode the electrode which was anode during the preceding half cycleDThis in turn permits the use of a higher voltage arc tube and an increase in the ratio of voltage drop across the arc tube tovoltage drop across the ballast filament, resulting in increased efficacy. To provide a voltage doubling effect for starting the lamp, one or two of the dio'desof the bridge may have a capacitor connected in parallel. These are small size capacitors since-they need only provide current enough to ignite the discharge and not to maintain the are. When the voltagedoublingeffect is not needed, the bridge rectifier may also be used along without 'any capacitor.
After ignition of the lamp, the bridge rectifier continues to operate the lamp or rectified current and the diodes must have current carrying capacity adequate for this burden. The real difficulty arises from the need to provide adequate heat-dissipating capacityfor the diodes. While silicon diodes are used *whichcan withstand a higher operatingtemperaturethangermanium diodes, the problem of assuring adequate heat dissipation in the confined environment of a high intensity discharge lamp whereof both the arcltube and the ballasting filament areintense sources oflheat, has remained acute.
SUMMARY OF THE INVENTION In accordance with our invention, adequate heatdissipating capacity for the four diodes of the bridge is achieved by heat-sinking one pair of diodes directly to the center contact ofthe base, andheat-sinking'the other pair of diodes directly to'the base shelLWe have found that such heat sinking may fortuitously be achieved by way of the required electrical connections 1 odes are disposed transverse to the lamps axis and soldered or brazed with very shortleads to the end of the base shell. The othersides of the four diodes are connected together in pairs to form the conjugate output points across which the arc tube and the ballast im- 2 pedance consisting of an incandescible filament are connected in series. Where a voltage doubling effect is desired, one or two of the diodes may be paralleled by a small capacitor. The assembly of the four diodes, and the capacitors when used, is potted in an electrical .resin which also serves to holdthe end contact in the desired spatial relationship relative to the base shell.
In a variant of the design, chip rectifiers are used in place of discrete encapsulated units. The chip rectifiers are stacked between the end contact and the outer face of the base shell with foils inbetween to serve as the conjugate output points. In yet another variant, an integral assembly composedof a good heat-dissipating substrate in which chip rectifiers and conductors are embedded is disposedbetweenthe end contact and the shell of the base.
DESCRIPTION OF DRAWINGS In the drawings wherein like reference characters indicate corresponding elements in the several views:
, FIG. 1 showsschematically the circuit interconnections of the arc tube, ballast filament and bridge rectifier. 7
'FIG. 2 illustrates a high pressure metal vapor arc lamp whereinthe invention is embodied. in preferred form.
FIG. 3 is an enlarged sectional view of the base showing heat sinking of the diodes to the end contact and to the base shell.
v FIG. 4illustrates a base extension collar which increases the separation betweenthe hot arctube and 'bridgerectifier in the base.
FIGS. 5a and 5b are sidesectional and end views respectively of a base showing a semi-integral bridge assembly constituting a variant of the invention.
FIG. 6 is a side-sectional view of a baseshowing a full integralassembly ofpellet diodes in a heat dissipating substrate.
DESCRIPTION or PREFERRED EMBODIMENTS The inventionis mose useful when embodied in the base of a self-ballasted highpressure mercury vapor lamp 1 as shown in FIGS. land 2. The lamp 1 comprises an outer glass envelope or. jacket 2 of ovoid shape. The neck 3 of the outer envelopeis closed by the usual re-entrant stem 4 through which extend stiff inlead wires 5, 6. The inner arctube 7 of quartz is provided at opposite ends with a pair of main discharge supporting electrodes 8, 9 to which connections are made by ribbon type inleads sealed throughthe flattened ends of the tube. Eachelectrode comprises a l a springy clamp 14. The are tube is supported in the harness by clamping its flat ends between metal bands l5, 16 which are welded to single side rod 12.
An incandescibleballast filament 17 is mounted to extend-axially alongside the arctube. It is connected to side rod 12 by conductor 18 and to electrode 8 by conductor 19; an insulated support wire 20 encirclesthe filament near its midpointto provide additional support. Side rod 12 connects main electrode 9 in series with ballast filament 17 to inlead 5 while main electrode 8 is connected directly to inlead 6. The outer envelope is filled with a non-reactive gas, suitably nitrogen, to reduce tungsten evaporation from filament 17. A pair of heat reflector discs 21 is mounted in the neck of the outer envelope just below the stem. These discs are necessary in the version of the lamp intended for base-up operation in order to reduce the temperature of the base and of the rectifier bridge components mounted within it. Zirconium getter rings 22 absorb any deleterious gas, particularly hydrogen, released during operation.
In the illustrated lamp, arc tube 7 contains a charge of mecury and an inert gas such as argon at a pressure below l millimeters of mercury. Alternatively, the lamp may contain metal halides in addition to the mercury charge, for instande sodium iodide and other metal halides. 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 preferably silicon diodes. In one lamp design rated at 120 volts A.C., 300 watts, the diodes are commerically available passivated and glass-encapsulated silicon diodes sold by General Electric Company and designated 1N5625. These are axial lead, avalanche type devices rated at 3.0 amperes and having a peak inverse voltage rating of 400 volts. As shown in FIG. 3, diodes D1 and D2 are mounted vertically in base 23 and depend below end contact 24 to which they are brazed or soldered with extremely short leads. Conveniently, the short leads are passed through holes in the end contact and the upper face of the end contact is covered with solder 25. Diodes D3 and D4 are mounted horizontally within the circular aperture in the dome end of base shell 26 to which they are soldered or brazed with extremely short leads. The assembly utilizes essentially zero lead length for the bridge connections on one side of each one of the four diodes and this gives maximum heat transfer to the end contact and screw shall of the base. These parts engage the conductive metal parts of the fixture socket, namely the center contact and shell respectively, and the arrangement thereby achieves optimum heatsinking capability. The end contact and base shell are preferably made of brass and the bridge may be assembled using l percent tin, 85 percent lead solder, which has a solidus temperature of 225C. to make soldered connections. v
In this embodiment, capacitors C1, C2 are connected in parallel with and close alongside diodes D3 and D4 respectively to provide a voltage doubling effect at starting. By using two capacitors, pulse transients which might damage the diodes are more effectively bypassed. Suitable capacitors are Sprague disc ceramic capacitors of 0.001 microfarad having a breakdown voltage rating of 1000 volts. These are high temperature capacitors assembled using high melting point solder and having an epoxy-dipped outer coating.
The inwardly directed ends of diodes D1 and D3 are joined together to form conjugate point j3, and similarly the inner ends of diodes D2 and D4 are joined together to form conjugate point j4. As illustrated, the diodes are connected for [forward conduction toward conjugate point j3 and away from conjugate point j4 so that the former is positive and the latter is negative. Teflon-coated stranded wires 27, 28 are used to make the connections between the bridge output points j3, j4 and the lamp inleads 4, 5.
After the bridge components have been mounted in place relative to the end contact and shell of the base, the entire assembly is potted using a filled resin 29 which is flame retardant and has good resistance to mechanical and thermal shock. A suitable material is an epoxy resin designated Scotchcast XRS 192 and sold by, Minnesota Mining and Manufacturing Company. The external configuration of base 23 is the same as that of a conventional (mogul size) base and it fits into the same kind of socket.
In the embodiment of FIG. 2, the base is fitted on the neck 3 of outer bulb 2 which has threads molded into the glass. A convenient way of assembling the parts is to first solder stranded wires 27, 28 to the outer ends of inleads S, 6 and slip flexible insulating sleeves over the joints. The base is next twisted counterclockwise about 2 k turns relative to the bulb, and then screwed on clockwise until firmly seated the twist being simultaneously removed thereby from the stranded wires. If the threads are smeared with a room temperaturesetting cement which is resistant to high temperatures prior to screwing the base on the neck of the bulb, a very secure fastening is achieved.
The present lamp is intended in part as a replacement for shorter-lived incandescant lamps. In order to perform similarly in the same fixture or optical arrangement, the effective light-center length of the present lamp, that is the distance from the end contact of the base to the center of the arc tube, may have to be increased to match that of the incandescent lamp which it replaces. As shown in FIG. 4, this may be done by interposing an insulating collar 30 between outer bulb 2 v and base 23. The collar may be of phenolic resin and is threaded internally at 31 to engage the threaded neck 3 of the bulb, and externally at 32 to engage the threaded base. As before, it is desirable to smear the threads with cement to assure a secure fastening. By increasing the separation between the hot arc tube and the base, the collar also serves to reduce the temperature of the bridge rectifier components.
Referring to FIGS. 50 and 5b, there is shown a variant which may be termed a semi-integral base-bridge assembly. In place of discrete glass-encapsulated unit, chip rectifiers are used consisting of flat semiconductor plates provided with solder pads on each face. The chip rectifiers, D1, D3 and D2, D4 are shown in vertically exploded fashion, stacked in pairs above the flat end 40 of base shell 41 on diametrically opposite sides of a central aperture 42. Conductive foils 43, 44 are interposed between the chip diodes in each stacked pair and correspond to conjugate output points +j3 and -j4; insulated conductors 45, 46 are attached thereto and pass out through aperture 42. An end plate having a raised central portion 47 which serves as an end contact has shoulder portions 48, 49 seated on and soldered to the top face of the upper chip in each stack. Capacitors C1, C2, if used, may be disposed above end plate 40 in the space to each side of the stacked diode chips as shown, or else within the base shell. The entire assembly is desirably potted in electrical resin (not shown) in similar manner to the construction of FIG. 3. The stacking of the chip rectifiers between the base shell and the end contact achieves high heat-dissipating capacity.
while D3 and D4 are embedded in the bottom face. The
diode chips are interconnected into a bridge circuit by conductors 51, 52 formed within the beryllium oxide and providing output junction points or terminals +j3 and j4. Integrated circuit unit 50 is seated on top of flat end 40 of base shell 41 so that diodes D3 and D4 contact the base shell. Junction points +j3 and j4 overlie central aperture 42 and have insulated conductors 45, 46 connected thereto. Diodes D1 and D2 are contacted by shoulder portions 48 and 49 of the end plate whereof the raised central portion 47 serves as end contact. The direct contact of diodes D1, D2 to the end contact, and the direct contact of diodes D3, D4 to the base shell assures good heat dissipation. Heat dissipation is further enhanced by the fact that all the diodes are embedded in the thermally heat-conductive substrate of unit 50 which is in direct contact with the base shell'and end contact. Capacitors C1, C2 if used may be chip capacitors and may also be embedded in the beryllium oxide. The end of the base may be filled out and protected by an electrically insulating resin 53.
What we claim as new and desire to secure by Letters Patent of the United States is:
l. A dual envelope internally ballasted arc discharge lamp comprising:
an outer vitreous jacket containing an inner arc tube and a ballast impedance,
a base fastened to said jacket comprising a metal shell having an end face and an end contact mounted thereabove and insulated therefrom,
a rectifier bridge located in said base and comprising four diodes,
two of the diodes having one side connected to the end contact and located next thereto for maximum heat transfer thereto,
two of the diodes having one side connected to the base shell and located next thereto for maximum heat transfer thereto,
said diodes being paired off with one connected to the end contact and one connected to the base shell in each pair, and the other side of the diodes in said pairs being connected together to provide conjugate output points across which said are tube and ballast impedance are connected in series.
2. A lamp as in claim 1 wherein said diodes are glass encapsulated axial lead silicon diodes and the connections for maximum heat transfer utilize a very short lead connected directly to the end contact or to the base shell.
3. A lamp as in claim 1 including at least one capacitor located in said base and connected in parallel with one of said diodes.
4. A lamp as in claim 1 wherein said diodes are chip rectifiers whereof one pair is located in contact with the end contact and another pair is located in contact with the shell of the base.
5. A lamp as in claim 1 wherein said diodes are chip rectifiers embedded and interconnected in a unit of electrically insulating but thermally conducting substrate, said unit being disposed between the end face and the end contact of said base.
6. A base for an electric lamp comprising:
a metal shell having a substantially flat end face with an aperture therein,
a metal end contact mounted above said end face and insulated therefrom,
a rectifier bridge in said base comprising four axial vlead glass encapsulated diodes, two of the diodes depending axially below said end contact and being connected thereto with very short leads for maximum heat transfer thereto,
two of the diodes being located transversely in said aperture and being connected with very short leads to the end face of said base shell for maximum heat transfer thereto,
said diodes being paired off with one connected to bridge rectifier and the end contact and one connected to the base shell in each pair, and the other side of the diodes in said paris being connected together to provide conjugate output points.
7. A base including a bridge rectifier as in claim 6 wherein said diodes are potted in an insulating resin serving to hold the end contact spaced and insulated from the base shell.
8. A base including a bridge rectifier as in claim 6 and at least one capacitor therein connected across one of said diodes.
9. A base including a bridge rectifier as in claim 6 and a pair of small capacitors connected across a pair of said diodes for a voltage doubling effect at starting, and wherein said diodes and capacitors are potted in an insulating resin which serves also to hold the end contact spaced and insulated from the base shell.