CA2036817C - Method of making an excitation coil for an electrodeless high intensity discharge lamp - Google Patents
Method of making an excitation coil for an electrodeless high intensity discharge lamp Download PDFInfo
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- CA2036817C CA2036817C CA002036817A CA2036817A CA2036817C CA 2036817 C CA2036817 C CA 2036817C CA 002036817 A CA002036817 A CA 002036817A CA 2036817 A CA2036817 A CA 2036817A CA 2036817 C CA2036817 C CA 2036817C
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/04—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing coils
- H01F41/10—Connecting leads to windings
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/04—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing coils
- H01F41/12—Insulating of windings
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J65/00—Lamps without any electrode inside the vessel; Lamps with at least one main electrode outside the vessel
- H01J65/04—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels
- H01J65/042—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels by an external electromagnetic field
- H01J65/048—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels by an external electromagnetic field the field being produced by using an excitation coil
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
Abstract
An excitation coil for a high intensity discharge lamp has an optimized configuration for maximizing efficiency and minimizing output light blockage. The coil comprises a conductive surface having a shape which corresponds to rotating a bilaterally symmetrical trapezoid about a coil center line in the same plane as the trapezoid without intersecting the center line. The conductive surface is disposed on a conductive core for efficient heat removal from the coil, resulting in reduced coil losses. In one embodiment, the coil cross section is increased by adding a rectangular portion to the trapezoidal portion, thereby extending the coil outwardly from the coil center line so as to remove heat from the coil more quickly without affecting light output from the lamp. The coil is constructed by separately casting the coil turns and brazing a connecting member therebetween, and then cutting a slit in each turn so as to electrically connect them in series.
Description
RD-19,801 Field of h- rnv n ;nn The present invention relates generally to electrodeless high intensity discharge (HID) lamps. More particularly, the present invention relates to a high efficiency excitation coil for an HID lamp having an optimized configuration which results in minimal blockage of light output from the lamp.
fiackgroLnd of h- rnv n ~~n In a high intensity discharge (HID) lamp, a medium to high pressure ionizable gas, such as mercury or sodium vapor, emits visible radiation upon excitation typically caused by passage of radio frequency (RF) current through the gas. One class of HID lamps comprises electrodeless lamps which generate an arc discharge by generating a solenoidal electric field in a high-pressure gaseous lamp fill. In particular, the lamp fill, or discharge plasma, is excited by RF current in an excitation coil surrounding an arc tube.
The arc tube and excitation coil assembly acts essentially as a transformer which couples RF energy to the plasma. That is, the excitation coil acts as a primary coil, and the plasma functions as a single-turn secondary. RF current in the excitation coil produces a varying magnetic field, in turn creating an electric field in the plasma which closes completely upon itself, i.e., a solenoidal electric field.
Current flows as a result of this electric field, resulting in a toroidal arc discharge in the arc tube.
RD-19,801 For efficient lamp operation, the excitation coil must not only have satisfactory coupling to the discharge plasma, but must also have low resistance and small size. A
practical coil configuration avoids as much light blockage by s the coil as possible and hence maximizes light output. One such coil configuration is described in commonly assigned U.S. Patent no. 4,812,702 of J.M. Anderson, issued March 14, 1989. The excitation coil of the Anderson patent has at least one turn of a conductor arranged generally upon the to surface of a torus having a substantially rhomboid or V-shaped cross section on either side of a coil center line.
Another exemplary coil configuration is described in commonly assigned, U.S. Patent no. 4,894,591, of H.L.
Witting, issued Jan. 16, 1990. The Witting application i5 describes an inverted excitation coil comprising first and second solenoidally-wound coil portions, each being disposed upon the surface of an imaginary cone having its vertex situated within the arc tube or within the volume of the other coil portion.
2o During operation of an HID lamp, as the temperature of the excitation coil increases, coil resistance increases, thereby resulting in higher coil losses. Hence, to increase coil efficiency. the excitation coil of an HID lamp is typically coupled to a heat sink for removing excess heat 2s from the excitation coil during lamp operation. Such a heat sink may comprise, for example, heat radiating fins coupled to the ballast used to provide radio frequency (RF) power to the lamp, as described in commonly assigned U.S. Pat. No.
4,910,439 of S.A. E1-Hamamsy and J.M. Anderson, issued March 30 20, 1990.
Although the hereinabove described HID lamp excitation coil configurations are suitable for many lighting applications, it is desirable to provide an excitation coil RD-19,801 exhibiting even higher efficiency, e.g. in excess of 90~, while providing efficient heat dissipation from the coil and causing minimal light blockage from the lamp.
Ob~eGt S Of h - TnyP_n_t i nn Accordingly, it is an object of the present invention to provide a high efficiency excitation coil for an electrodeless HID lamp having an optimized configuration which avoids as much light blockage from the lamp as practicable.
Another object of the present invention is to provide a high efficiency excitation coil for an electrodeless HID lamp having effectual means for removing heat from the coil without reducing light output from the lamp.
Still another object of the present invention is to provide a method of making a high efficiency excitation coil for an electrodeless HID lamp.
Shy Of hTnvenrinn The foregoing and other objects of the present invention are achieved in a new and improved excitation coil for an electrodeless HID lamp exhibiting very high efficiency and causing only minimal light blockage from the lamp. To these ends, the coil configuration is optimized in terms of the coupling coefficient between the coil and the arc discharge, and the quality factor Q of the coil. The overall shape of the excitation coil of the present invention is generally that of a surface formed by rotating a bilaterally symmetrical trapezoid about a center line situated in the same plane as the trapezoid, but which line does not intersect the trapezoid. The two parallel sides of the trapezoid are unequal in length, with the smaller side being situated toward the center of the coil surface. Preferably, RD-19,801 the corners of the trapezoid are curved. According to the present invention, although the number of coil turns may be varied, depending upon the particular application thereof, the overall shape remains the same. In an alternative S embodiment, the generally trapezoidal cross section is modified by adding a portion of rectangular cross section at the outer portion of the coil so that the longer of the two parallel sides of the trapezoid coincides with one of the sides of the rectangle, resulting in a larger cross sectional area and thus more efficient heat dissipation from the excitation coil, but without causing additional light blockage.
An excitation coil of the present invention may be constructed by separately casting the coil turns and connecting them together by brazing a connecting member between each of the turns. Slits are then made in the turns in order to connect them electrically in series.
Alternatively, a corresponding portion may be cut out of each coil turn so that a single, solid connecting member with the coil terminals connected thereto may be brazed between the coil turns. Slits are then made in the connecting member so that the coil turns are electrically connected in series.
Brief Descr,'_ntion of the DrawinQ~
The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which:
Figure lA is a partly schematic view of an HID lamp system, including a top view of an electrodeless HID lamp employing a high efficiency single-turn excitation coil in accordance with a preferred embodiment of the present invention;
RD-19,801 Figure 1B is an isometric view of the single-turn excitation coil and arc tube of Figure lA;
Figure 1C is a cross sectional view of the single-turn excitation coil of Figure lA taken along line 1C-1C
thereof;
Figure 2 is a graph of excitation coil quality factor Q versus contour angle A for a constant cross sectional area useful in understanding the present invention;
Figure 3A is a partly schematic view of an HID lamp system, including a top view of an HID lamp employing a high efficiency two-turn excitation coil in accordance with a preferred embodiment of the present invention;
Figure 3B is an isometric view of the two-turn excitation coil of Figure 3A;
Figure 3C is a cross sectional view of the two-turn excitation coil of Figure 3A taken along line 3C-3C thereof;
Figure 3D is a transectional isometric view of the two-turn excitation coil of Figure 3B taken along line 3D-3D;
Figure 4 is transectional isometric view of a two-turn excitation coil according to an alternative embodiment of the present invention;
Figure 5A is transectional isometric view of a two-turn excitation coil according to an alternative embodiment of the present invention;
Figure 5B illustrates the conductor employed in the excitation coil of Figure 5A to connect the coil turns thereof in series;
Figure 6 is transectional isometric view of a two-turn excitation coil according to an alternative embodiment of the present invention;
Figure 7 is a cross sectional view of a three-turn excitation coil in accordance with a preferred embodiment of the present invention;
RD-19,801 Figure 8 is a cross sectional view of a four-turn excitation coil in accordance with a preferred embodiment of the present invention;
Figure 9A is an isometric view of an alternative s embodiment of the two-turn excitation coil of Figures 3A-3D;
and Figure 9B is a cross sectional view of the two-turn excitation coil of Figure 6A taken along line 6B-6B thereof.
to Figures lA through 1C illustrate an electrodeless HID lamp system 10 employing a single-turn excitation coil 12 surrounding an arc tube 14 in accordance with a preferred embodiment of the present invention. The arc tube is preferably formed of a high temperature glass, such as fused i5 quartz, or an optically transparent ceramic, such as polycrystalline alumina. By way of example and clarity of illustration, arc tube 14 is shown as having a spherical shape. However, arc tubes of other shapes may be desirable, depending upon the application. For example, arc tube 14 may 2o have the shape of a short cylinder, or "pillbox", having rounded edges, if desired, as described in commonly assigned U.S. Patent no. 4,810,938, issued to P. D. Johnson, J. T.
Dakin and J. M. Anderson on March 7, 1989. As explained in the Johnson et al. patent, such a structure promotes more z5 nearly isothermal operation, thus decreasing thermal losses and hence increasing efficiency.
Arc tube 14 contains a fill in which a solenoidal arc discharge is excited during lamp operation. A suitable fill, described in U.S. Patent no. 4,810,938, cited 3o hereinabove, comprises a sodium halide, a cerium halide and xenon combined in weight proportions to generate visible radiation exhibiting high efficacy and good color rendering RD-19,801 _ 7 _ capability at white color temperatures. For example, such a fill according to the Johnson and Anderson patent may comprise sodium iodide and cerium chloride, in equal weight proportions, in combination with xenon at a partial pressure s of about 500 torr. Another suitable fill is described in U.S. Patent no. 4,972,120 of H.L. Witting, issued November 20, 1990, and assigned to the instant assignee. The fill of the Witting application comprises a combination of a lanthanum halide, a sodium halide, a cerium halide and io xenon or krypton as a buffer gas. For example, a fill according to the Witting application may comprise a combination of lanthanum iodide, sodium iodide, cerium iodide, and 250 torr partial pressure of xenon.
As illustrated in Figure lA, radio frequency (RF) i5 power is applied to the HID lamp by an RF ballast 16 via excitation coil 12 coupled thereto. Heat sink means 18 are shown thermally coupled to coil 12 and ballast 16 for removing heat from excitation coil 12. In operation, RF
current in coil 12 results in a varying magnetic field which 20 produces within arc tube 14 an electric field which completely closes upon itself. Current flows through the fill within arc tube 14 as a result of this solenoidal electric field, producing a toroidal arc discharge therein.
Suitable operating frequencies for RF ballast 16 are in the z5 range from 1 to 30 megahertz (l~iz), an exemplary operating frequency being 13.56 N~iz.
A suitable ballast 16 is described in commonly assigned, U.S. patent 5,047,692 of J.C. Borowiec and S.A. El-Hamamsy, issued September 10, 1991. The lamp 3o ballast of the cited patent application is a high-efficiency ballast comprising a Class-D power amplifier and a tuned network. The tuned network includes an ~,~~~~~~_ a' _8_ RD-19,801 integrated tuning capacitor network and heat sink. In particular, a series/blocking capacitor and a parallel tuning capacitor are integrated by sharing a common capacitor plate.
Furthermore, the metal plates of the parallel tuning capacitor comprise heat sink planes of a heat sink used to remove excess heat from the excitation coil of the lamp.
Alternatively, as described in the E1-Hamamsy and Anderson patent application cited hereinabove, a suitable electrodeless HID lamp ballast includes a network of capacitors that is used both for impedance matching and heat sinking. In particular, a pair of parallel-connected capacitors has large plates that are used to dissipate heat generated by the excitation coil and arc tube.
In accordance with the present invention, the configuration of excitation coil 12 is optimized to maximize coil efficiency E~oii and minimize light blockage by the coil.
To these ends, the coil configuration is optimized in terms of the coil quality factor Q and the coupling coefficient k between coil 12 and the arc discharge according to the following expression:
k2Qa Ecoil ° k2Qa + 1 where a is a constant, the value of which depends on the size of arc tube 14. From the above expression, it is clear that coil efficiency E~oil is maximized by maximizing the product k2Q. The optimum coil configuration is thus obtained through an iterative process.
A single-turn excitation coil having an optimized configuration in accordance with a preferred embodiment of the present invention is shown in top view in Figure lA, in isometric view in Figure 1B and in cross section in Figure 1C. The overall shape of the excitation coil is generally -RD-19,801 that of a surface formed by rotating a bilaterally symmetrical trapezoid about a center line situated in the same plane as the trapezoid, but which line does not intersect the trapezoid. The two parallel sides of the trapezoid are unequal in length, with the smaller side being situated toward the center line. Preferably, the corners of the trapezoid are curved. In Figure 1C, the coil center line is designated as the z-axis, and the x-axis is illustrated as being perpendicular thereto and bisecting the single-turn coil. The inner radius of the excitation coil extends from the center line along the x-axis to the smaller side of the trapezoid and is designated as R1; and the outer radius extends from the center line along the x-axis to the outer edge of the coil and is designated as R2. Along the z-axis, or center line, the distance from the x-axis to the inner edge of the coil is designated as hl, while the distance from the x-axis to the outer edge of the coil is designated as h2.
Figure 2 is a graph of quality factor Q of the excitation coil versus contour angle 8 for a constant cross sectional area A, the contour angle A being defined herein as the angle determined by the slope of each of the nonparallel sides of the trapezoid. As shown in Figure 2, the quality factor Q is a maximum for 8 ~ 28' for the chosen constant cross sectional area A. Hence, for contour angle A =28', the cross section of the optimized coil configuration is defined in terms of the following ratios:
R
h2 = 1. 2, and hl = 3.2, where R represents the height of the trapezoid and is defined by the expression R = R2 - R1. For maximum coil efficiency - 10 ~-RD-19,801 with an excitation coil having a cross sectional area A, the aforesaid ratios are maintained constant, while the inner and outer radii of the excitation coil may be varied, depending on the size of the arc tube.
The principles of the present invention are applicable to excitation coils having any number of turns.
For example, a two-turn excitation coil 20 in accordance with a preferred embodiment of the present invention is illustrated in Figures 3A through 3D. The cross sectional area and contour angle B are substantially the same as those for the single-turn coil described hereinabove. The two turns of the coil are separated by a gap 22, e.g. up to approximately 4 millimeters wide for an arc tube having an arc diameter of approximately 12 millimeters, i.e.
corresponding to of = 0.3.
In a preferred embodiment, the two-turn excitation coil is formed by separately casting two coil turns, each including a terminal 23, and connecting them together by brazing a triangular piece of conductor 24 (shown in Figures 3A and 3D) therebetween. Lastly, a slit 26 is made in each of the turn castings in order to connect the turns electrically in series. Other suitably configured conductors may be used to connect the separately cast coil turns together. For example, as shown in Figure 4, a rectangular piece of conductor 124 is brazed between the coil turns with slits 126 following the contour thereof in order to connect the coil turns electrically in series. As illustrated in Figures SA and 5B, in another alternative embodiment, a connecting conductor 224 may be folded in an accordion-like manner and brazed between the coil turns. Slits 226 are made in the coil turns to electrically connect them in'series. In an alternative method, as illustrated in Figure 6, a corresponding portion is removed from each coil turn, and a single, solid connecting member 250, including terminals 23, RD-19,801 is brazed within the gap formed by removing the corresponding portion from each coil turn. Diagonal slits 256 are then made in the connecting member so as to connect the coil turns in series. As will be appreciated by those of ordinary skill in the art, any of the hereinabove described methods of making an excitation coil of the present invention may be employed to construct coils having any number of turns.
Figures 7 and 8 are cross sectional views of excitation coils having three and four turns, respectively, in accordance with the principles of the present invention.
In particular, the cross sectional area and contour angle A
are substantially the same for the three-turn and four-turn coils as those for the single-turn coil of Figure 1 and the two-turn coils of Figures 3-6. The coil turns are connected in series in a manner described hereinabove with reference to the two-turn coils of Figure 3-6.
In Figures 1 and 3-8, the excitation coils are each illustrated as being comprised of solid metal. However, since HID lamp excitation coils typically operate at high frequencies, as explained hereinabove, coil currents are carried substantially within a skin depth of the coil surface. At 13.56 MHz, for example, the skin depth of copper is only about one mil. Therefore, if the coil core is not required to remove heat from the coil, i.e. another method of heat dissipation is being employed, then the excitation coil can be made as a hollow structure such as by casting, metal spinning, or electro-disposition of a conductive material onto a mold. For a coil so constructed, heat dissipation may be provided, for example, by circulating water according to a method well-known in the art.
An alternative embodiment of an excitation coil having a conductive surface disposed over a conductive core in accordance with a preferred embodiment of the present invention is shown in Figures 9A and 9B. By way of - 12 - )~36~1'r RD-19,801 illustration, the alternative embodiment of Figures 9A and 9B
is shown for a two-turn excitation coil. The coil cross section has been increased with respect to that of Figures 3-7 by, in effect, adding a rectangular portion 30 to the substantially trapezoidal cross section at the outer portion of the coil. As a result, heat is removed from the coil more quickly, without blocking additional light output from the lamp .
While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by Way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
fiackgroLnd of h- rnv n ~~n In a high intensity discharge (HID) lamp, a medium to high pressure ionizable gas, such as mercury or sodium vapor, emits visible radiation upon excitation typically caused by passage of radio frequency (RF) current through the gas. One class of HID lamps comprises electrodeless lamps which generate an arc discharge by generating a solenoidal electric field in a high-pressure gaseous lamp fill. In particular, the lamp fill, or discharge plasma, is excited by RF current in an excitation coil surrounding an arc tube.
The arc tube and excitation coil assembly acts essentially as a transformer which couples RF energy to the plasma. That is, the excitation coil acts as a primary coil, and the plasma functions as a single-turn secondary. RF current in the excitation coil produces a varying magnetic field, in turn creating an electric field in the plasma which closes completely upon itself, i.e., a solenoidal electric field.
Current flows as a result of this electric field, resulting in a toroidal arc discharge in the arc tube.
RD-19,801 For efficient lamp operation, the excitation coil must not only have satisfactory coupling to the discharge plasma, but must also have low resistance and small size. A
practical coil configuration avoids as much light blockage by s the coil as possible and hence maximizes light output. One such coil configuration is described in commonly assigned U.S. Patent no. 4,812,702 of J.M. Anderson, issued March 14, 1989. The excitation coil of the Anderson patent has at least one turn of a conductor arranged generally upon the to surface of a torus having a substantially rhomboid or V-shaped cross section on either side of a coil center line.
Another exemplary coil configuration is described in commonly assigned, U.S. Patent no. 4,894,591, of H.L.
Witting, issued Jan. 16, 1990. The Witting application i5 describes an inverted excitation coil comprising first and second solenoidally-wound coil portions, each being disposed upon the surface of an imaginary cone having its vertex situated within the arc tube or within the volume of the other coil portion.
2o During operation of an HID lamp, as the temperature of the excitation coil increases, coil resistance increases, thereby resulting in higher coil losses. Hence, to increase coil efficiency. the excitation coil of an HID lamp is typically coupled to a heat sink for removing excess heat 2s from the excitation coil during lamp operation. Such a heat sink may comprise, for example, heat radiating fins coupled to the ballast used to provide radio frequency (RF) power to the lamp, as described in commonly assigned U.S. Pat. No.
4,910,439 of S.A. E1-Hamamsy and J.M. Anderson, issued March 30 20, 1990.
Although the hereinabove described HID lamp excitation coil configurations are suitable for many lighting applications, it is desirable to provide an excitation coil RD-19,801 exhibiting even higher efficiency, e.g. in excess of 90~, while providing efficient heat dissipation from the coil and causing minimal light blockage from the lamp.
Ob~eGt S Of h - TnyP_n_t i nn Accordingly, it is an object of the present invention to provide a high efficiency excitation coil for an electrodeless HID lamp having an optimized configuration which avoids as much light blockage from the lamp as practicable.
Another object of the present invention is to provide a high efficiency excitation coil for an electrodeless HID lamp having effectual means for removing heat from the coil without reducing light output from the lamp.
Still another object of the present invention is to provide a method of making a high efficiency excitation coil for an electrodeless HID lamp.
Shy Of hTnvenrinn The foregoing and other objects of the present invention are achieved in a new and improved excitation coil for an electrodeless HID lamp exhibiting very high efficiency and causing only minimal light blockage from the lamp. To these ends, the coil configuration is optimized in terms of the coupling coefficient between the coil and the arc discharge, and the quality factor Q of the coil. The overall shape of the excitation coil of the present invention is generally that of a surface formed by rotating a bilaterally symmetrical trapezoid about a center line situated in the same plane as the trapezoid, but which line does not intersect the trapezoid. The two parallel sides of the trapezoid are unequal in length, with the smaller side being situated toward the center of the coil surface. Preferably, RD-19,801 the corners of the trapezoid are curved. According to the present invention, although the number of coil turns may be varied, depending upon the particular application thereof, the overall shape remains the same. In an alternative S embodiment, the generally trapezoidal cross section is modified by adding a portion of rectangular cross section at the outer portion of the coil so that the longer of the two parallel sides of the trapezoid coincides with one of the sides of the rectangle, resulting in a larger cross sectional area and thus more efficient heat dissipation from the excitation coil, but without causing additional light blockage.
An excitation coil of the present invention may be constructed by separately casting the coil turns and connecting them together by brazing a connecting member between each of the turns. Slits are then made in the turns in order to connect them electrically in series.
Alternatively, a corresponding portion may be cut out of each coil turn so that a single, solid connecting member with the coil terminals connected thereto may be brazed between the coil turns. Slits are then made in the connecting member so that the coil turns are electrically connected in series.
Brief Descr,'_ntion of the DrawinQ~
The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which:
Figure lA is a partly schematic view of an HID lamp system, including a top view of an electrodeless HID lamp employing a high efficiency single-turn excitation coil in accordance with a preferred embodiment of the present invention;
RD-19,801 Figure 1B is an isometric view of the single-turn excitation coil and arc tube of Figure lA;
Figure 1C is a cross sectional view of the single-turn excitation coil of Figure lA taken along line 1C-1C
thereof;
Figure 2 is a graph of excitation coil quality factor Q versus contour angle A for a constant cross sectional area useful in understanding the present invention;
Figure 3A is a partly schematic view of an HID lamp system, including a top view of an HID lamp employing a high efficiency two-turn excitation coil in accordance with a preferred embodiment of the present invention;
Figure 3B is an isometric view of the two-turn excitation coil of Figure 3A;
Figure 3C is a cross sectional view of the two-turn excitation coil of Figure 3A taken along line 3C-3C thereof;
Figure 3D is a transectional isometric view of the two-turn excitation coil of Figure 3B taken along line 3D-3D;
Figure 4 is transectional isometric view of a two-turn excitation coil according to an alternative embodiment of the present invention;
Figure 5A is transectional isometric view of a two-turn excitation coil according to an alternative embodiment of the present invention;
Figure 5B illustrates the conductor employed in the excitation coil of Figure 5A to connect the coil turns thereof in series;
Figure 6 is transectional isometric view of a two-turn excitation coil according to an alternative embodiment of the present invention;
Figure 7 is a cross sectional view of a three-turn excitation coil in accordance with a preferred embodiment of the present invention;
RD-19,801 Figure 8 is a cross sectional view of a four-turn excitation coil in accordance with a preferred embodiment of the present invention;
Figure 9A is an isometric view of an alternative s embodiment of the two-turn excitation coil of Figures 3A-3D;
and Figure 9B is a cross sectional view of the two-turn excitation coil of Figure 6A taken along line 6B-6B thereof.
to Figures lA through 1C illustrate an electrodeless HID lamp system 10 employing a single-turn excitation coil 12 surrounding an arc tube 14 in accordance with a preferred embodiment of the present invention. The arc tube is preferably formed of a high temperature glass, such as fused i5 quartz, or an optically transparent ceramic, such as polycrystalline alumina. By way of example and clarity of illustration, arc tube 14 is shown as having a spherical shape. However, arc tubes of other shapes may be desirable, depending upon the application. For example, arc tube 14 may 2o have the shape of a short cylinder, or "pillbox", having rounded edges, if desired, as described in commonly assigned U.S. Patent no. 4,810,938, issued to P. D. Johnson, J. T.
Dakin and J. M. Anderson on March 7, 1989. As explained in the Johnson et al. patent, such a structure promotes more z5 nearly isothermal operation, thus decreasing thermal losses and hence increasing efficiency.
Arc tube 14 contains a fill in which a solenoidal arc discharge is excited during lamp operation. A suitable fill, described in U.S. Patent no. 4,810,938, cited 3o hereinabove, comprises a sodium halide, a cerium halide and xenon combined in weight proportions to generate visible radiation exhibiting high efficacy and good color rendering RD-19,801 _ 7 _ capability at white color temperatures. For example, such a fill according to the Johnson and Anderson patent may comprise sodium iodide and cerium chloride, in equal weight proportions, in combination with xenon at a partial pressure s of about 500 torr. Another suitable fill is described in U.S. Patent no. 4,972,120 of H.L. Witting, issued November 20, 1990, and assigned to the instant assignee. The fill of the Witting application comprises a combination of a lanthanum halide, a sodium halide, a cerium halide and io xenon or krypton as a buffer gas. For example, a fill according to the Witting application may comprise a combination of lanthanum iodide, sodium iodide, cerium iodide, and 250 torr partial pressure of xenon.
As illustrated in Figure lA, radio frequency (RF) i5 power is applied to the HID lamp by an RF ballast 16 via excitation coil 12 coupled thereto. Heat sink means 18 are shown thermally coupled to coil 12 and ballast 16 for removing heat from excitation coil 12. In operation, RF
current in coil 12 results in a varying magnetic field which 20 produces within arc tube 14 an electric field which completely closes upon itself. Current flows through the fill within arc tube 14 as a result of this solenoidal electric field, producing a toroidal arc discharge therein.
Suitable operating frequencies for RF ballast 16 are in the z5 range from 1 to 30 megahertz (l~iz), an exemplary operating frequency being 13.56 N~iz.
A suitable ballast 16 is described in commonly assigned, U.S. patent 5,047,692 of J.C. Borowiec and S.A. El-Hamamsy, issued September 10, 1991. The lamp 3o ballast of the cited patent application is a high-efficiency ballast comprising a Class-D power amplifier and a tuned network. The tuned network includes an ~,~~~~~~_ a' _8_ RD-19,801 integrated tuning capacitor network and heat sink. In particular, a series/blocking capacitor and a parallel tuning capacitor are integrated by sharing a common capacitor plate.
Furthermore, the metal plates of the parallel tuning capacitor comprise heat sink planes of a heat sink used to remove excess heat from the excitation coil of the lamp.
Alternatively, as described in the E1-Hamamsy and Anderson patent application cited hereinabove, a suitable electrodeless HID lamp ballast includes a network of capacitors that is used both for impedance matching and heat sinking. In particular, a pair of parallel-connected capacitors has large plates that are used to dissipate heat generated by the excitation coil and arc tube.
In accordance with the present invention, the configuration of excitation coil 12 is optimized to maximize coil efficiency E~oii and minimize light blockage by the coil.
To these ends, the coil configuration is optimized in terms of the coil quality factor Q and the coupling coefficient k between coil 12 and the arc discharge according to the following expression:
k2Qa Ecoil ° k2Qa + 1 where a is a constant, the value of which depends on the size of arc tube 14. From the above expression, it is clear that coil efficiency E~oil is maximized by maximizing the product k2Q. The optimum coil configuration is thus obtained through an iterative process.
A single-turn excitation coil having an optimized configuration in accordance with a preferred embodiment of the present invention is shown in top view in Figure lA, in isometric view in Figure 1B and in cross section in Figure 1C. The overall shape of the excitation coil is generally -RD-19,801 that of a surface formed by rotating a bilaterally symmetrical trapezoid about a center line situated in the same plane as the trapezoid, but which line does not intersect the trapezoid. The two parallel sides of the trapezoid are unequal in length, with the smaller side being situated toward the center line. Preferably, the corners of the trapezoid are curved. In Figure 1C, the coil center line is designated as the z-axis, and the x-axis is illustrated as being perpendicular thereto and bisecting the single-turn coil. The inner radius of the excitation coil extends from the center line along the x-axis to the smaller side of the trapezoid and is designated as R1; and the outer radius extends from the center line along the x-axis to the outer edge of the coil and is designated as R2. Along the z-axis, or center line, the distance from the x-axis to the inner edge of the coil is designated as hl, while the distance from the x-axis to the outer edge of the coil is designated as h2.
Figure 2 is a graph of quality factor Q of the excitation coil versus contour angle 8 for a constant cross sectional area A, the contour angle A being defined herein as the angle determined by the slope of each of the nonparallel sides of the trapezoid. As shown in Figure 2, the quality factor Q is a maximum for 8 ~ 28' for the chosen constant cross sectional area A. Hence, for contour angle A =28', the cross section of the optimized coil configuration is defined in terms of the following ratios:
R
h2 = 1. 2, and hl = 3.2, where R represents the height of the trapezoid and is defined by the expression R = R2 - R1. For maximum coil efficiency - 10 ~-RD-19,801 with an excitation coil having a cross sectional area A, the aforesaid ratios are maintained constant, while the inner and outer radii of the excitation coil may be varied, depending on the size of the arc tube.
The principles of the present invention are applicable to excitation coils having any number of turns.
For example, a two-turn excitation coil 20 in accordance with a preferred embodiment of the present invention is illustrated in Figures 3A through 3D. The cross sectional area and contour angle B are substantially the same as those for the single-turn coil described hereinabove. The two turns of the coil are separated by a gap 22, e.g. up to approximately 4 millimeters wide for an arc tube having an arc diameter of approximately 12 millimeters, i.e.
corresponding to of = 0.3.
In a preferred embodiment, the two-turn excitation coil is formed by separately casting two coil turns, each including a terminal 23, and connecting them together by brazing a triangular piece of conductor 24 (shown in Figures 3A and 3D) therebetween. Lastly, a slit 26 is made in each of the turn castings in order to connect the turns electrically in series. Other suitably configured conductors may be used to connect the separately cast coil turns together. For example, as shown in Figure 4, a rectangular piece of conductor 124 is brazed between the coil turns with slits 126 following the contour thereof in order to connect the coil turns electrically in series. As illustrated in Figures SA and 5B, in another alternative embodiment, a connecting conductor 224 may be folded in an accordion-like manner and brazed between the coil turns. Slits 226 are made in the coil turns to electrically connect them in'series. In an alternative method, as illustrated in Figure 6, a corresponding portion is removed from each coil turn, and a single, solid connecting member 250, including terminals 23, RD-19,801 is brazed within the gap formed by removing the corresponding portion from each coil turn. Diagonal slits 256 are then made in the connecting member so as to connect the coil turns in series. As will be appreciated by those of ordinary skill in the art, any of the hereinabove described methods of making an excitation coil of the present invention may be employed to construct coils having any number of turns.
Figures 7 and 8 are cross sectional views of excitation coils having three and four turns, respectively, in accordance with the principles of the present invention.
In particular, the cross sectional area and contour angle A
are substantially the same for the three-turn and four-turn coils as those for the single-turn coil of Figure 1 and the two-turn coils of Figures 3-6. The coil turns are connected in series in a manner described hereinabove with reference to the two-turn coils of Figure 3-6.
In Figures 1 and 3-8, the excitation coils are each illustrated as being comprised of solid metal. However, since HID lamp excitation coils typically operate at high frequencies, as explained hereinabove, coil currents are carried substantially within a skin depth of the coil surface. At 13.56 MHz, for example, the skin depth of copper is only about one mil. Therefore, if the coil core is not required to remove heat from the coil, i.e. another method of heat dissipation is being employed, then the excitation coil can be made as a hollow structure such as by casting, metal spinning, or electro-disposition of a conductive material onto a mold. For a coil so constructed, heat dissipation may be provided, for example, by circulating water according to a method well-known in the art.
An alternative embodiment of an excitation coil having a conductive surface disposed over a conductive core in accordance with a preferred embodiment of the present invention is shown in Figures 9A and 9B. By way of - 12 - )~36~1'r RD-19,801 illustration, the alternative embodiment of Figures 9A and 9B
is shown for a two-turn excitation coil. The coil cross section has been increased with respect to that of Figures 3-7 by, in effect, adding a rectangular portion 30 to the substantially trapezoidal cross section at the outer portion of the coil. As a result, heat is removed from the coil more quickly, without blocking additional light output from the lamp .
While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by Way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
Claims (29)
1. A method of making an excitation coil for an electrodeless high intensity discharge lamp having at least two coil turns, comprising:
separately casting each respective coil turn so that said excitation coil comprises a conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil;
brazing a conductive member between each respective coil turn; and cutting a slit in each respective coil turn so as to couple the coil turns electrically in series with each other.
separately casting each respective coil turn so that said excitation coil comprises a conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil;
brazing a conductive member between each respective coil turn; and cutting a slit in each respective coil turn so as to couple the coil turns electrically in series with each other.
2. The method of claim 1 wherein said step of casting further includes forming a terminal on two of said coil turns, said terminals being adapted to be coupled to a radio frequency power supply.
3. The method of claim 1 wherein said step of casting further includes forming said trapezoid with rounded edges.
4. The method of claim 1 wherein said step of casting further includes forming said trapezoid with a height R, said short parallel side with a length 2h1, and said long parallel side with a length 2h2, the cross section of said excitation coil being determined such that:
5. The method of claim 1, further comprising providing heat conducting means contained substantially within said conductive surface for removing heat from said excitation coil.
6. The method of claim 5 wherein said step of providing heat conducting means comprises situating said conductive surface on a heat conductive core.
7. A method of making an excitation coil for an electrodeless high intensity discharge lamp having at least two turns, comprising:
casting said coil turns so that said excitation coil comprises a conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil;
removing a corresponding portion from each of said coil turns to form corresponding gaps therein;
brazing a conductive member to said coil turns to fill in said gaps; and cutting diagonal slits in said conductive member so as to connect said coil turns electrically in series.
casting said coil turns so that said excitation coil comprises a conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil;
removing a corresponding portion from each of said coil turns to form corresponding gaps therein;
brazing a conductive member to said coil turns to fill in said gaps; and cutting diagonal slits in said conductive member so as to connect said coil turns electrically in series.
8. The method of claim 7 wherein said conductive member includes two terminals for coupling said coil to a radio frequency power supply.
9. The method of claim 7 wherein said trapezoid has a height R, said short parallel side has a length 2h1, and said long parallel side has a length 2h2, the cross section of said excitation coil being determined such that:
10. The method of claim 7, further comprising providing heat conducting means contained substantially within said conductive surface for removing heat from said excitation coil.
11. The method of claim 10 wherein said step of providing heat conducting means comprises situating said conductive surface on a heat conductive core.
12. An excitation coil for exciting an arc discharge in an electrodeless high intensity discharge lamp, comprising:
a conductive surface configured to form at least one coil turn, said conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil; and means for coupling said excitation coil to a radio frequency power supply.
a conductive surface configured to form at least one coil turn, said conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil; and means for coupling said excitation coil to a radio frequency power supply.
13. The excitation coil of claim 12 wherein said trapezoid has rounded edges.
14. The excitation coil of claim 12 wherein said trapezoid has a height R, said short parallel side has a length h1, and said long parallel side has a length h2, the cross section of said excitation coil being determined such that:
15. The excitation coil of claim 12 wherein said conductive surface is configured to form at least two turns electrically connected in series.
16. The excitation coil of claim l2,further comprising heat conducting means contained substantially within said conductive surface for removing heat from said excitation coil.
17. The excitation coil of claim 16 wherein said heat conducting means comprises a heat conductive core on which said conductive surface is disposed.
18. The excitation coil of claim 16 wherein:
said conductive surface further comprises a rectangular portion disposed on said long parallel side of said trapezoid so that said long parallel side coincides with one side of said rectangular portion, the shape of said coil further being determined by rotating said rectangular portion about said center line; and said heat conducting means comprises a heat conductive core on which said conductive surface is disposed.
said conductive surface further comprises a rectangular portion disposed on said long parallel side of said trapezoid so that said long parallel side coincides with one side of said rectangular portion, the shape of said coil further being determined by rotating said rectangular portion about said center line; and said heat conducting means comprises a heat conductive core on which said conductive surface is disposed.
19. The excitation coil of claim 18,further comprising rounded edges.
20. The excitation coil of claim 18 wherein said conductive surface is configured to form at least two turns electrically connected in series.
21. An electrodeless high intensity discharge lamp, comprising:
a light-transmissive arc tube for containing a fill;
an excitation coil disposed about said arc tube for exciting an arc discharge in said fill, said excitation coil comprising a conductive surface configured to form at least one coil turn, said conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil; and means for coupling said excitation coil to a radio frequency power supply.
a light-transmissive arc tube for containing a fill;
an excitation coil disposed about said arc tube for exciting an arc discharge in said fill, said excitation coil comprising a conductive surface configured to form at least one coil turn, said conductive surface having a shape determined by rotating a substantially bilaterally symmetrical trapezoid about a center line which does not intersect said trapezoid, said trapezoid having a relatively short parallel side and a relatively long parallel side, said short parallel side being disposed toward said center line to form the inner surface of said coil; and means for coupling said excitation coil to a radio frequency power supply.
22. The lamp of claim 21 wherein said trapezoid has rounded edges.
23. The lamp of claim 21 wherein said trapezoid has a height R, said short parallel side has a length h1, and said long parallel side has a length h2, the cross section of said excitation coil being determined such that:
24. The lamp of claim 21 wherein said conductive surface is configured to form at least two turns electrically connected in series.
25. The lamp of claim 21, further comprising heat conducting means contained substantially within said conductive surface for removing heat from said excitation coil.
26. The lamp of claim 25 wherein said heat conducting means comprises a heat conductive core on which said conductive surface is disposed.
27. The lamp of claim 25 wherein:
said conductive surface further comprises a rectangular portion disposed on said long parallel side of said trapezoid so that said long parallel side coincides with one side of said rectangular portion, the shape of said coil further being determined by rotating said rectangular portion about said center line; and said heat conducting means comprises a heat conductive core on which said conductive surface is disposed.
said conductive surface further comprises a rectangular portion disposed on said long parallel side of said trapezoid so that said long parallel side coincides with one side of said rectangular portion, the shape of said coil further being determined by rotating said rectangular portion about said center line; and said heat conducting means comprises a heat conductive core on which said conductive surface is disposed.
28. The lamp of claim 27 wherein said excitation coil further comprises rounded edges.
29. The lamp of claim 27 wherein said conductive surface is configured to form at least two turns electrically connected in series.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/493,266 US5039903A (en) | 1990-03-14 | 1990-03-14 | Excitation coil for an electrodeless high intensity discharge lamp |
| US07/554,496 US5042139A (en) | 1990-03-14 | 1990-07-19 | Method of making an excitation coil for an electrodeless high intensity discharge lamp |
| US493,266 | 1990-07-19 | ||
| US554,496 | 1990-07-19 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2036817A1 CA2036817A1 (en) | 1991-09-15 |
| CA2036817C true CA2036817C (en) | 2002-02-12 |
Family
ID=27051020
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002036817A Expired - Fee Related CA2036817C (en) | 1990-03-14 | 1991-02-21 | Method of making an excitation coil for an electrodeless high intensity discharge lamp |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5042139A (en) |
| JP (1) | JP2606976B2 (en) |
| CA (1) | CA2036817C (en) |
| DE (1) | DE4107263C2 (en) |
| NL (1) | NL9100097A (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5214357A (en) * | 1991-11-14 | 1993-05-25 | General Electric Company | Low-loss l-c drive circuit for an electrodeless high intensity discharge lamp |
| EP0612099B1 (en) * | 1993-02-16 | 1996-09-25 | Koninklijke Philips Electronics N.V. | Electrodeless high-pressure discharge lamp |
| US5619103A (en) * | 1993-11-02 | 1997-04-08 | Wisconsin Alumni Research Foundation | Inductively coupled plasma generating devices |
| US6137237A (en) * | 1998-01-13 | 2000-10-24 | Fusion Lighting, Inc. | High frequency inductive lamp and power oscillator |
| US5952784A (en) * | 1998-08-28 | 1999-09-14 | General Electric Company | Electrodeless high intensity discharge lamps |
| US20100109831A1 (en) * | 2008-10-31 | 2010-05-06 | General Electric Company | Induction coil without a weld |
| US9299527B2 (en) * | 2012-12-27 | 2016-03-29 | Chang Gung University | Gas discharge tubes for surcharge suppression |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4220839A (en) * | 1978-01-05 | 1980-09-02 | Topsil A/S | Induction heating coil for float zone melting of semiconductor rods |
| JPS6448391A (en) * | 1987-04-27 | 1989-02-22 | Shinetsu Handotai Kk | Single winding induction heating coil used in floating zone melting method |
| US4810938A (en) * | 1987-10-01 | 1989-03-07 | General Electric Company | High efficacy electrodeless high intensity discharge lamp |
| US4910439A (en) * | 1987-12-17 | 1990-03-20 | General Electric Company | Luminaire configuration for electrodeless high intensity discharge lamp |
| US4812702A (en) * | 1987-12-28 | 1989-03-14 | General Electric Company | Excitation coil for hid electrodeless discharge lamp |
| US4894591A (en) * | 1988-09-06 | 1990-01-16 | General Electric Company | Inverted Excitation coil for HID lamps |
| FR2657454B1 (en) * | 1990-01-23 | 1995-07-13 | Aerospatiale | PROCESS FOR THE PRODUCTION OF ELECTROMAGNETIC WINDINGS. |
-
1990
- 1990-07-19 US US07/554,496 patent/US5042139A/en not_active Expired - Fee Related
-
1991
- 1991-01-21 NL NL9100097A patent/NL9100097A/en not_active Application Discontinuation
- 1991-02-21 CA CA002036817A patent/CA2036817C/en not_active Expired - Fee Related
- 1991-03-07 DE DE4107263A patent/DE4107263C2/en not_active Expired - Fee Related
- 1991-03-12 JP JP3070331A patent/JP2606976B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE4107263A1 (en) | 1991-09-19 |
| NL9100097A (en) | 1991-10-01 |
| US5042139A (en) | 1991-08-27 |
| CA2036817A1 (en) | 1991-09-15 |
| JP2606976B2 (en) | 1997-05-07 |
| DE4107263C2 (en) | 1993-11-04 |
| JPH05101895A (en) | 1993-04-23 |
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| EEER | Examination request | ||
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