Information
-
Patent Grant
-
6297583
-
Patent Number
6,297,583
-
Date Filed
Thursday, October 8, 199825 years ago
-
Date Issued
Tuesday, October 2, 200122 years ago
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Inventors
-
Original Assignees
-
Examiners
- Patel; Nimeshkumar D.
- Gerike; Matthew John
Agents
- Reising, Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
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CPC
-
US Classifications
Field of Search
US
- 313 160
- 313 161
- 313 607
- 313 313
- 313 242
- 313 248
- 313 613
- 313 283
- 313 634
- 315 248
- 315 344
- 315 39
- 315 57
- 315 85
- 315 70
- 445 23
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International Classifications
- H01J150
- H01J2310
- H01J2976
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Abstract
An inductively driven gas discharge lamp assembly (40) includes an electrodeless lamp (42), an inductive drive coil (44) disposed about the lamp, and a shield (10) disposed over an end portion (50) of the lamp. The shield (10) has a number of turns (12) of electrically conductive material, such as wire, with each of the turns being disposed generally coaxially about the central, longitudinal axis (20) of the drive coil (44). The turns (12) together form a continuous spiral helix and are shorted together via a number of electrical conductors (14) that are angularly disposed about the axis (20). These electrical conductors (14) extend generally perpendicularly to the turns (12) and are connected to the ground node (26) of a d.c. to a.c. inverter circuit 46 that is used to drive coil 44. This arrangement provides good r.f. electric field and magnetic field shielding and permits the use of relatively few turns (12) at a relatively large spacing of the turns so as to minimize the interference of the shield (10) on the amount of light emitted from the lamp (42). Also disclosed is another embodiment (30) in which the turns (32) each comprise a single loop rather than a continuous spiral helix.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates in general to inductively driven electrodeless gas discharge lamps and, in particular, to electromagnetic shielding of radio frequency interference emitted from the drive coils used to energize such lamps.
2. Description of the Related Art
Inductively driven electrodeless gas discharge lamps utilize a solenoidal coil driven with alternating current to produce a plasma discharge within the lamp envelope. Alternating current flow through the coil generates a time-varying magnetic field that impinges upon the ionizable gas fill within the lamp, causing it to produce the plasma discharge. The gas fill can be an inert or other rare earth gas, such as neon, which produces a visible discharge when excited by the magnetic field.
Often, these lamps are driven at radio frequencies resulting in strong magnetic and electric fields that radiate well beyond the lamp envelope. In many applications, these radiated fields can detrimentally effect the operation of nearby circuits and sensors. For example, when used in automotive applications, the drive coils used to energize these lamps could detrimentally influence such things as engine sensors and the vehicle's electronic compass. Accordingly, it is well known to shield the electromagnetic radiation emanating from the drive coil. Although electric and magnetic field shielding is most effectively accomplished with a grounded, electrically conductive, ferromagnetic enclosure, such an arrangement is not practical since it would also shield the light transmitted by the lamp, making the entire assembly useless for its intended purpose.
Consequently, shielding is typically accomplished using a conductive screen or wire mesh that extends over all or a portion of the lamp envelope. See, for example, U.S. Pat. No. 5,397,966 to Vrionis et al. One problem with the use of a wire mesh for shielding purposes is that it can cause a significant reduction in the light output from the lamp due to the large total area covered by the wire making up the mesh. Vrionis et al. also disclose a shield made up of a plurality of electrically conductive fingers that extend generally in the direction of the axis of the induction coil. This arrangement of conductive fingers helps reduce any detrimental effect that the shield has on the efficiency of the lamp operation; however, it is believed that it also results in a correspondingly reduced effectiveness of the magnetic shielding effect.
SUMMARY OF THE INVENTION
The invention provides an electrodeless gas discharge lamp assembly which provides good electric and magnetic field shielding while minimizing its impact on the light output of the lamp. The lamp assembly includes a gas discharge lamp having a sealed envelope containing an ionizable gas fill, an inductive drive coil disposed about the lamp envelope, and a shield disposed over an end portion of the lamp envelope. The shield has a number of turns of electrically conductive material, such as wire, with each of the turns being disposed generally coaxially about the central, longitudinal axis of the drive coil. The turns are shorted together via a number of electrical conductors that are angularly disposed about the axis. These electrical conductors extend generally perpendicularly to the turns, either axially or radially, or both, relative to the longitudinal axis about which they are disposed. When connected in circuit, the electrical conductors are grounded. This arrangement provides good r.f. electric field and magnetic field shielding and permits the use of relatively few turns at a relatively large spacing of the turns so as to minimize the interference of the shield on the amount of light emitted from the lamp.
In one embodiment, the turns of the shield together comprise a continuous electrical path extending in a spiral helix about the end portion of the lamp. Each turn is shorted to each of the other turns at ninety degree intervals about their central, longitudinal axis. In another embodiment, each turn comprises a single loop, with some or all of the loops being shorted together via the electrical conductors.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred exemplary embodiment of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and:
FIG. 1
is a perspective view of a preferred embodiment of a shield of the present invention;
FIG. 2
is a perspective view of a second embodiment of a shield of the invention; and
FIG. 3
is a perspective view of a shield as in
FIG. 1
used as a part of an inductively driven lamp assembly.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in
FIG. 1
, an r.f. shield
10
of the present invention includes a number of turns
12
of an electrically conductive material, such as metal wire, with each turn
12
being electrically shorted to its adjacent turns via a number of perpendicularly extending conductors
14
. Turns
12
together comprise a coil that defines continuous electrical path extending as a spiral helix from a first end
16
to a second end
18
. Each turn
12
comprises an approximately 360° loop that is coaxially disposed about a longitudinal axis
20
of shield
10
. These turns are shorted to each other by electrical conductors
14
at ninety degree intervals about axis
20
. Conductors
14
can be formed of the same electrically conductive material as turns
12
(e.g., metal wire). Each conductor
14
extends perpendicularly across each of the turns
12
from a first turn
22
to a last turn
24
where the conductors
14
are connected in circuit to a ground node
26
.
Preferably, each of the turns
12
are shorted together via the conductors
14
, although it will be understood that one or more turns could be left disconnected from conductors
14
. Alternatively, each of the conductors
14
can be electrically connected to some, but not all of the turns
12
such that each turn
12
is grounded via at least one of the conductors
14
. Although four such conductors
14
are shown, it will be appreciated that more or less conductors
14
could be used, as desired for a particular application. Additionally, the conductors
14
need only be generally perpendicular to turns
12
; that is, they can either run perpendicular to turns
12
, as shown, or can wrap somewhat helically about longitudinal axis
20
. Other such variations will become apparent to those skilled in the art.
Referring now to
FIG. 2
, there is shown a second embodiment of an r.f. shield of the invention, designated generally as
30
. Shield
30
can be exactly the same as shield
10
of
FIG. 1
, except that it includes a number of turns
32
, each of which is an individual loop rather than one turn of a continuous spiral helix. The turns
32
are coaxially disposed about longitudinal axis
20
and are only connected to one another by the electrical conductors
14
. The various design considerations and variations discussed above and below in connection with
FIGS. 1 and 3
apply equally to shield
30
of FIG.
2
.
FIG. 3
depicts shield
10
as it may be implemented as a part of an inductively driven gas discharge lamp assembly
40
. In addition to shield
10
, lamp assembly
40
includes an electrodeless lamp
42
, an inductive drive coil
44
, and a d.c. to a.c. inverter circuit
46
. Lamp
42
can be a conventional gas discharge lamp having an ionizable gas fill enclosed within a sealed envelope. Neon or other rare gases that produce a plasma discharge when subjected to high frequency magnetic fields can be used. Inductive drive coil
44
is disposed about lamp
42
such that both it and shield
10
are coaxially disposed about longitudinal axis
20
. Coil
44
can be wound using insulated copper wire and can be wound directly on lamp
42
or on a separate bobbin (not shown). Coil
44
is driven with an r.f. alternating current to thereby produce a time-varying magnetic field that produces the plasma discharge within lamp
42
. The r.f. current is generated by inverter circuit
46
which can be a self-oscillating circuit that operates off a d.c. supply, such as a battery voltage (labelled
+
B). Suitable inverter circuits are well known to those skilled in the art. The electric field shielding provided by r.f. shield
10
is realized by connection of conductors
14
to the input ground
26
. Of course, shield
10
could also be connected to another low impedance node, such as
+
B.
As shown in
FIG. 3
, lamp
42
includes a base portion
48
and an end portion
50
which is generally hemispherical in shape. Shield
10
has a complementary conformation that provides a close fit over end portion
50
. Electrical conductors
14
therefore extend arcuately from the first turn
22
(where they extend in a generally radial direction) to the last turn
24
(where they extend in a generally axial direction). Rather than using wire for turns
12
and conductors
14
, these electrical paths could be formed as electrically conductive traces on the surface of lamp
42
. Alternatively, these electrical paths could be formed as a part of a lens or other light transmissive cover than is placed over the end portion
50
of lamp
42
. In any of these variations shield
10
need not be in contact lamp
42
, but can instead have a larger overall size such that it extends over lamp
42
without coming into contact with it. Moreover, if desired for a particular application, shield
10
can extend further down towards the base
48
of lamp
42
such that it surrounds all or a part of drive coil
44
.
Rather than separately connecting each of the electrical conductors
14
to the ground node
26
, all but one of the conductors
14
can terminate at a lower loop
52
with that one conductor
14
then being connected to ground node
26
. Similarly, rather than using lower loop
52
, all but one of the conductors
14
can terminate on the last turn
24
of shield
10
with that one conductor then being connected to ground node
26
. Furthermore, where one of the ends of drive coil
44
is connected to a low impedance node, such as ground, the electrical conductors
14
can be connected directly to that one end of coil
44
rather than separately wired to inverter circuit
46
.
As will be appreciated by those skilled in the art, the spacing of the individual turns depicted in
FIG. 3
is exemplary only and the actual spacing for any particular lighting application can be selected based upon the relative need for shielding versus total light output. In this regard, the shield can be made from wire or other conductors that are much thinner than that used for drive coil
44
.
R.F. shield
10
results in much less surface area of the lamp envelope being covered than occurs when using a mesh or screen for shielding. Also, since the turns
12
are oriented coaxially along the same axis as drive coil
44
, shield
10
provides better magnetic shielding than the conductive finger arrangement disclosed in the above-noted U.S. Pat. No. 5,397,966 to Vrionis et al.
It will thus be apparent that there has been provided in accordance with the present invention a shielded gas discharge lamp assembly which achieves the aims and advantages specified herein. It will of course be understood that the foregoing description is of a preferred exemplary embodiment of the invention and that the invention is not limited to the specific embodiment shown. Various changes and modifications will become apparent to those skilled in the art. For example, when used with a lamp having a relatively planar light emitting surface, the shield can comprise concentric turns with radially-extending electrical conductors. All such variations and modifications are intended to come within the scope of the appended claims.
Claims
- 1. An inductively driven gas discharge lamp assembly, comprising:an electrodeless gas discharge lamp having a sealed envelope containing an ionizable gas fill, said envelope having at least one light transmissive end portion; an inductive drive coil disposed about said envelope, said drive coil having a central, longitudinal axis that extends through said lamp envelope, whereby an alternating current driven through said drive coil produces a time-varying magnetic field that impinges upon said gas fill; characterized in that: the lamp assembly further comprises a shield disposed over said end portion of said lamp envelope, said shield having a number of turns of electrically conductive material with each of said turns being disposed generally coaxially about said longitudinal axis in spaced relation from the others of said turns, wherein at least some of said turns are shorted together by a number of electrical conductors that are angularly disposed about said axis and that extend generally perpendicularly to said turns.
- 2. A lamp assembly as defined in claim 1, wherein said turns of said electrically conductive material comprises a continuous electrical path extending in a spiral helix about said end portion.
- 3. A lamp assembly as defined in claim 2, wherein said electrically conductive material and said electrical conductors comprise metal wire.
- 4. A lamp assembly as defined in claim 1, wherein each of said turns of said shield comprises a single loop with at least some of said loops being shorted together via said electrical conductors.
- 5. A lamp assembly as defined in claim 4, wherein said electrically conductive material and said electrical conductors comprise metal wire.
- 6. A lamp assembly as defined in claim 1, wherein said shield is in contact with said lamp envelope.
- 7. A lamp assembly as defined in claim 1, wherein said drive coil comprises a number of turns of insulated wire.
- 8. A lamp assembly as defined in claim 7, wherein said insulated wire is wound directly on said lamp envelope.
- 9. A lamp assembly as defined in claim 1, wherein each of said turns of said shield are shorted together via said electrical conductors.
- 10. A lamp assembly as defined in claim 1, wherein each of said electrical conductors intersects at least some of said turns of said shield.
- 11. A lamp assembly as defined in claim 1, wherein each of said electrical conductors cross and electrically connect to at least some of said turns of said shield.
- 12. A lamp assembly as defined in claim 1, wherein said shield and said end portion of said lamp are generally hemispherical and wherein each of said electrical conductors extend arcuately from a first, smaller diameter turn to a last, larger diameter turn.
- 13. A lamp assembly as defined in claim 12, wherein said conductors extend radially proximate said first turn and extend axially proximate said last turn.
- 14. A lamp assembly as defined in claim 1, further comprising a d.c. to a.c. inverter circuit for providing operating power to said drive coil, said inverter circuit having at least two inputs with one of said inputs being a ground node, wherein said shield is electrically coupled to said ground node.
US Referenced Citations (20)