Information
-
Patent Grant
-
6594885
-
Patent Number
6,594,885
-
Date Filed
Tuesday, December 26, 200023 years ago
-
Date Issued
Tuesday, July 22, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Vo; Peter
- Tugbang; A. Dexter
Agents
- Fay, Sharpe, Fagan, Minnich & McKee, LLP
-
CPC
-
US Classifications
Field of Search
US
- 029 6021
- 029 606
- 029 605
- 029 453
- 336 83
- 336 205
- 336 206
- 336 207
- 336 208
- 264 27219
- 264 2722
- 264 236
- 264 347
-
International Classifications
-
Abstract
A method of assembling a coil includes forming a ferrite core having a top end, a bottom end, an inner opening extending from the top end to the bottom end, a cylindrical outer surface, and a step portion formed near the bottom end, the step portion extending past the outer surface. A first high dielectric material is applied on the outer surface of the ferrite core, then a conductive wire is wound onto the high dielectric material, whereafter a second high dielectric material is applied over the conductive wire.
Description
BACKGROUND OF THE INVENTION
An electrodeless fluorescent lamp (EFL) implements a coil design in its configuration. Such a coil design includes a cylindrical ferrite core, a bobbin and conductive insulative wire wound around a portion of the bobbin.
FIG. 1
illustrates a prior art high-temperature plastic threaded bobbin
10
which may be used in such a design. As depicted, bobbin
10
includes a high-temperature plastic base portion
12
and an integrated threaded high-temperature plastic chimney portion
14
. Chimney portion
14
is molded to include grooves
16
on the exterior cylindrical surface. A cylindrical ferrite core, not shown, is placed within the interior
18
of chimney
14
and conductive wire (not shown) is wound around chimney
14
by following the groove pattern
16
. A tape or shrink-tubing product would then be placed around the wound conductive wire to maintain the wire in position and maintain the integrity of the coil.
In the prior art coil, there are at least two ends of the conductive wire wound around the chimney
14
of bobbin
10
. The ends of these wires are passed through the base
12
for attachment to an electronic board or alternatively attached to plugs attached to the underside of base
12
. The plugs may be received by the electronic board for connection of the coil configuration. Threads
16
provide a built-in pitch wire spacing for the conductive wire.
Chimney
14
is a split element
20
whereby when conductive wire is wound around chimney
14
in the groove pattern
16
, chimney
14
is compressed around the ferrite core. Hook or holding elements
22
act to maintain the core securely within interior
18
. The underside of base
12
is formed such that the bottom portion of ferrite core is held within the chimney
14
. Bobbin
10
acts as an electrically insulating layer between the conductive wire and the ferrite core sufficient to prevent electrical breakdowns from occurring within the coil. The conductive wire itself may be insulated, and capable of continually withstanding temperatures approximately 250° C.
During operation of a coil, the highest temperature in the core body will occur in the middle height location of the core. Therefore, in
FIG. 1
the area having the highest temperature on bobbin
10
would be approximately at location
24
. For an RF coil assembly intended to work with EFL products in the 120-volt and 230-volt range, the temperature at this center point
24
could reach 250°. This being the case, it is necessary for bobbin
10
to be made of a material that has a maximum allowable service temperature capable of withstanding such a temperature level. Temperatures at the ends of the coil are around 200° C.
A drawback of a coil manufactured using bobbin
10
of
FIG. 1
, is the requirement of using the high-temperature material in order to withstand the temperatures generated during operation of the coil. This necessitates the use of expensive high temperature materials. Further, bobbin
10
uses a significant amount of such an expensive material due to the chimney feature. Additionally there is a significant amount of cost involved in manufacturing the bobbin
10
with threads
16
.
Therefore, the present invention looks to manufacture a simplified RF coil assembly with decreased costs as compared to existing coil assemblies, where the coil assembly meets expectations and operational requirements for use with an electrodeless fluorescent lamps.
BRIEF SUMMARY OF THE INVENTION
A cylindrical ferrite core includes a top-end, bottom-end and inner opening extending from the top end to the bottom end. An outer surface of the cylindrical core includes a step portion formed at the bottom end of the core, extending past the outer circumference of the non-step portion. A first high dielectric material is formed over at least a substantial portion of the outer surface of the cylindrical core to provide an insulative barrier. A length of conductive wire having a first end and a second end is wound around the first high dielectric material located over the outer surface of the cylindrical ferrite core. A second high dielectric material is then placed or located over the length of the conductive wire. This configuration seals the conductive wire between the two high dielectric materials and insulating the conductive wire from the ferrite core. A coil holder is provided having a base portion with a base opening formed substantially in a centered area in the base of the coil holder, the base opening is sufficiently sized to provide a passage way to the inner opening of the ferrite core. A snap-fit portion having a plurality of snap-fit fingers extending from the base portion engage the step portion of the cylindrical ferrite core, whereby the core is locked into engagement with the coil holder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
depicts a prior art high-temperature plastic threaded bobbin;
FIG. 2
shows a cylindrical ferrite core having a step portion;
FIG. 3
illustrates a conductive wire used in the present invention;
FIG. 4
illustrates a first high-dielectric material formed over the ferrite core of
FIG. 2
;
FIG. 5
depicts the conductive wire wound around the insulative material of
FIG. 4
;
FIG. 6
shows the second insulative material formed over the conductive wiring;
FIG. 7
sets forth a coil holder of the present invention;
FIG. 8
shows a side view of a snap-fit finger of the coil holder.
FIG. 9
illustrates a snap-fit engagement between the ferrite core and coil holder;
FIG. 10
depicts an EFL device designed using the coil of the present invention; and
FIGS. 11
,
12
and
13
show alternative connection concepts of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Turning to
FIG. 2
, illustrated is a first embodiment of a ferrite core or tube
30
designed in accordance with the teachings of the present invention. Core
30
includes a top end
32
, a bottom end
34
, an inner opening
36
extending from the top end
32
to the bottom end
34
. An outer surface
38
of a cylindrical formation with a step portion
40
extending past the outer surface
38
. In the present embodiment, step
40
extends in a cylindrical manner approximately 1 mm around the circumference past outer surface
38
of ferrite core
30
. It is understood that step
40
may be vary from the mentioned 1 mm. A notch
42
may be optionally provided in core
30
to assist in holding a coil winding in place. This concept will be discussed in greater detail below.
The core
30
of
FIG. 2
is manufactured by use of a form. Alternatively, the core could be machined by taking a larger dimension core and machining it down to a desired formation. If the core is machined, it is preferred to provide an annealing of the cores to maintain a quality factor (Q) desirable for operation of an EFL component. Another manner of forming the core is by an extrusion process.
Ferrite core
30
which may be used in a preferred embodiment of the present invention, has the following parameters. The core geometry and material must provide a given inductance value without causing the need for geometric changes in the EFL device in which it is used. Parameters for a core intended to be used with an EFL device previously described, has an outside diameter (OD) of 17±0.35 mm; an inside diameter (ID) of 8.6±0.25 mm; and a length of 30±0.7 mm.
In the present invention, a conductive wire
50
such as in
FIG. 3
, is to be wound around the ferrite core
30
(of FIG.
2
). Wire
50
, in one embodiment, is a bare copper magnetic wire. Winding wire
50
onto core
30
is conceptually different from prior art coils which incorporate a bobbin feature configuration to carry the wound wire. It is to be appreciated that winding the conductive wire directly onto the ferrite core
30
could result in conduction between windings of the wire through the ferrite core
30
. Particularly, there is a concern that even if an insulated wire is wound around the ferrite core, during the life of the coil assembly, the wire would break down causing conduction between the wire and core, causing a malfunction of the coil. This possibility emphasizes the need to provide some sort of insulating material between the ferrite core
30
and the conductive wire
50
.
FIG. 4
depicts a first high dielectric material
60
applied to ferrite core
30
. As can be seen, the step portion
40
and a small portion of the upper end
32
of core
30
are not encompassed within first dielectric
60
. It is to be appreciated that the windings of wire
50
will not be wound as far down core
30
to include step
40
or go to upper end
32
. Therefore the first dielectric material
60
does not need to cover these portions of the core
30
. However, in another embodiment, it is of course possible to include the dielectric material to cover core step
40
or upper end
32
.
In selecting the appropriate coating material for a first high dielectric material
60
, it is desirable to select a material which will maintain thermal stability at a continuous temperature substantially equal to or greater than 250° C., and will have a temperature expansion co-efficient which matches ferrite core
30
or otherwise be malleable. It is to be appreciated that some applications may be able to operate at lower temperatures, such as systems designed for table lamps instead of ceiling fixtures, and low wattage systems. Such material should also not adversely affect the ferrite material electromagnetic performance (i.e. dielectric strength, resistivity, magnetic flux density, permeability, and Q). Material
60
should also provide sufficient insulation between the coil formed by wire
50
, and core
30
, and between adjacent turns of wire
50
. The coating for the high dielectric material used in the present embodiment is also beneficially of a low cost, easy to apply and provides the appropriate material strength and adhesion to maintain the coil active for a life span of approximately 15,000 hours or more. Coatings which may be used include at least silicon/rubber/polymer coatings, ceramic coatings and vitreous/glass coatings. Specific types of coatings which meet the foregoing requirements include but are not limited to a material TSE 326, a silicon product from General Electric, PTFE and PFA which are Teflon products from Dupont, and Xydar G-930, a liquid-crystal polymer (LCP).
The first high dielectric material
60
is used to not only provide an insulative layer between the core and conductive wire, but also to provide space insulation.
It should be emphasized here that the required thickness will play a part in determining the method of coating ferrite core
30
. For example, spray coating techniques are able to apply up to 1 mil/per application. To build up a large thickness with spray coating, the process will need to be applied repeatedly. Dip-coating can build a thickness of up to approximately 50 mils per application. In this technique, the core is placed on a rod or other holder, is dipped into a coating material. Once removed from the material, core
30
now covered in the high dielectric coating, is spun to evenly distribute the coating on the core. Another technique includes brushing on the coating material. Therefore, when choosing the method of application, it may be useful, though not necessary, to have electromagnetic calculations made to establish the required insulation thickness for the first high dielectric layer
60
. The manner of obtaining such calculations are known in the art by one of ordinary skill.
With attention to ceramic coatings, ceramics can withstand very high temperatures and they provide a room temperature, short-time curability and high manufacturability if needed for winding. By controlling the chemistry and density (porosity) the dielectric properties can be optimized (low permitivity and losses) to match that of polymers. To promote adhesion, the reactivity between the ceramic coating and the ferrite core is optimized. Selected ceramics should not degrade the electromagnetic characteristics of the core. The material should be stable for the life of the lamp (i.e. greater than 15,000 hours) at the operating temperatures. The coefficient of thermal expansion of the coating in the core should be matched so that there is no cracking and spallation of the coating during the curing and the subsequent use cycles. The high dielectric strength and resistivity are required of the material to provide insulation between the coil wire and the core. Some ceramic adhesives and coating systems include but are not limited to Brewer AlPO
4
from General Electric, P-78 and No. 31 from Sauereisen and Ceramadip 538N from Aremco.
Turning to
FIG. 5
, core
30
is shown with a first covering of a high dielectric material
60
around which is wound wire
50
in the form of a coil
70
.
One embodiment of the present invention, the first high dielectric material
60
, is cured only to a point where it is still of a substantially tacky consistency. Conductive wire
50
which may be a bare copper wire is wound onto the partially cured high dielectric layer
60
using a known winding process. The tackiness of the partially cured layer
60
assists in maintaining the wire position on the ferrite core
30
as the coil is wound. Such a winding procedure will provide the required winding pitch, and also help hold the wire in place. However, if it is found the winding of conductive wire
50
in this process is too time-consuming, an alternative process is to fully cure the first high dielectric material
60
prior to the winding process.
Winding of conductive wire
50
on first high dielectric material
60
in a coil formation
70
, as shown in
FIG. 5
, results in a first end portion
72
and a second end portion
74
. These end portions will, eventually, be connected to an electronic circuit such as in an EFL assembly. To secure the winding, one of the first end and the second may be inserted into notch
42
, of core
30
. The winding of conductive wire
50
as coil
70
may be accomplished by one of many known winding techniques.
It is noted that in one embodiment, conductive wire
50
used to form coil
70
, may be a rectangular wire. Such an embodiment is considered to provide the benefit of maintaining desired wire spacing. Further, a benefit of rectangular wire over square wire is that square wire generally has thinner insulation at its corners and thus a lower voltage breakdown capability.
Once the coil
70
has been formed over material
60
and around core
30
, a second high dielectric material
80
is applied over wire coil
70
as depicted in FIG.
6
. The coil ends
72
and
74
are not encompassed within this second high dielectric material
80
. The second layer of high dielectric material assists in holding the wire coil
70
(
FIG. 5
) in place, and seals it from the environment to retard oxidation of the wire in the high-temperature environment.
The entire coil assembly
90
of
FIG. 6
, includes core
30
, first high dielectric material
60
, coil wire winding
70
, and the second high dielectric material
80
. This assembly is cured so dielectric coatings
60
and
80
form into a solid material. This solid maintains coil
70
in its precisely wound shape, forming the hermetic seal to prevent the oxidation of the wire, and electrically insulate it from the surface of ferrite core
30
to prevent electrical breakdown of the coil.
Turning now to
FIG. 7
, shown is a coil holder
100
according to concepts of the present invention. Coil holder
100
includes a base portion
110
having a base opening
120
formed substantially at a centered area of the coil holder
100
. The base opening
120
is sufficiently sized to provide a passageway to the inner opening of the ferrite core
30
once attached to holder
100
. Also included is a snap-fit portion comprising a plurality of snap-fit fingers
130
, which extend from the base portion
110
. In one embodiment the snap-fit portion consists of four evenly spaced snap-fit fingers
130
. However, more or less fingers may also be used. Snap-fit fingers
130
are designed to receive step
40
of core
30
. This concept is depicted in more detail in
FIG. 8
which provides a side view of one of snap-fit fingers
130
for engaging step
40
of ferrite core
30
. As can be seen from this figure, step
40
fits into snap-fit finger
130
, which has a bottom ledge portion
140
and an upper support or top tab
150
. To allow for more flexibility, snap-fingers
130
are designed such that the top tabs
150
are tapered in a vertical direction.
In one preferred embodiment of the present invention, the overall core height is 30 mm, where the step is 3 mm. The step outer diameter is 19.02 mm, and the core body outside diameter is 17.02 and the inner opening is 8.56 mm in diameter. Each of the dimensions have a ±2% tolerance. The snap-fit finger connection's preferred dimensions for the present embodiment include an inner groove diameter of 19.50 mm±0.1% (i.e. a diameter corresponding to the four snap fingers), an overall individual snap finger height of 9.3 mm±0.5% (
152
), a snap finger inner opening height dimension of 3.2 mm±0.05% (
154
), an upper depth of 0.8 mm±0.05% (
156
), and a lower depth of 1.0 mm±0.05% (
158
).
Coil holder
100
is secured to the coil assembly
90
as shown in FIG.
9
. Since coil holder
100
is far simpler in design than a prior art bobbin, and since it does not need to endure temperatures nearly as high as the prior bobbin designs, it may be manufactured at a much lower cost.
Through-holes such as
160
are provided as passageways for first end
72
and/or second end
74
to pass through the bottom side of base
110
. It is to be understood that in the wiring process, first end wire
72
may pass through the inner portion
36
of core
30
and therefore not be required to use a through-hole but rather will pass through the back side of base
110
via center portion
120
. The back side of base
110
, can have pins
162
, attached to which are connected the first and second ends
72
and
74
. Connection between pins
160
and ends
72
,
74
can be made by a clamp connection, soldering or other known connection technique. Pins
136
, are then capable of being inserted into female receptacles of a larger electronic component.
Turning to
FIG. 10
, depicted is an EFL configuration. A lighting element
170
is shown inserted into the inner opening
36
of core
30
of coil assembly
90
. Pins
160
connected to at least ends
72
,
74
are inserted into a power source
180
causing the lamp to function as an electrodeless fluorescent lamp.
It is to be appreciated that in addition to the snap-fit technology described, the present invention may also include the use of a coil holder using a press-fit assembly. The press-fit assembly such as shown in
FIGS. 11 and 12
include both an outside press fit and an inside press fit. Particularly, core holder
190
of
FIG. 11
includes prongs
200
spaced such that they are slightly outside the outer dimension of core
210
. As illustrated, core
210
is similar to core
30
, but is symmetrical throughout its length. As core
210
is pressed to holder
190
, pressure from impingement of core
210
with pins
200
, hold core
210
in place. Turning attention to
FIG. 12
, inside press-fit construction is shown with prongs
220
of core holder
230
, spaced so as to exert a holding force on the inside passageway
240
of core
200
. Again, core
280
is symmetrical throughout its outer surface.
Turning to another embodiment, shown in
FIG. 13
, is a snap-fit assembly using a grooved ferrite core
250
. In this arrangement, in place of the ledge or step portion
40
of core
30
, core
250
includes a groove
260
. In this embodiment, snap finger
270
is designed to snap into engagement with groove
260
of core
250
.
While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those skilled in the art. It is therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.
Claims
- 1. A method of assembling a coil comprising:forming a ferrite core having a top end, a bottom end, an inner opening extending from the top end to the bottom end, a cylindrical outer surface, and a step portion formed near the bottom end, the step portion extending past the outer surface; applying a first high dielectric material onto the outer surface of the ferrite core, the first high dielectric material being in a partially cured state such that the first high dielectric material has a tacky compliant quality; winding a conductive wire onto the partially cured first high dielectric material, including embedding at least a portion of the conductive wire into the partially cured first high dielectric material, holding the wound conductive wire in a secure position; applying a second high dielectric material over the conductive wire; and completing the curing of the first high dielectric material, including forming a hermetic seal around the conductive wire.
- 2. The method according to claim 1, wherein:the curing causes the first high dielectric material and the second high dielectric material to form into a single solid mass, wherein the conductive wire is held in a fixed position.
- 3. The method according to claim 1 further including:forming a coil holder having, i) a base portion with a base opening formed substantially at a centered area of the coil holder, the base opening being sufficiently sized to provide a passage way to the inner opening of core, and (i) a plurality of snap fit fingers extending from the base portion.
- 4. The method according to claim 3 further including:inserting the step portion of the cylindrical ferrite core into the snap fit fingers of the coil holder, wherein the core is locked into engagement with the coil holder.
- 5. The method according to claim 1 wherein the first high dielectric material is a material different from the second high dielectric material.
- 6. The method according to claim 1 wherein the steps of applying the first and second high dielectric materials include at least one of coating, spraying, dripping and brushing.
- 7. A method of assembling a coil comprising:forming a ferrite core having a top end, a bottom end, an inner opening extending from the top end to the bottom end, a cylindrical outer surface, and a step portion formed near the bottom end, the step portion extending past the outer surface; applying a first high dielectric material, in a partially cured state having a tacky compliant quality, onto the outer surface of the ferrite core; winding a conductive wire onto the first high dielectric material, including embedding at least a portion of the conductive wire into the partially cured dielectric material, thereby holding the wound conductive wire in a secure position; and applying a second high dielectric material over the conductive wire.
- 8. The method according to claim 7 further including:curing the first high dielectric material and the second high dielectric material into a single solid mass, wherein the conductive wire is held in a fixed position.
- 9. The method according to claim 8 whereinthe step of curing includes forming a hermetic seal around the conductive wire.
- 10. The method according to claim 7 further including:forming a coil holder having, i) a base portion with a base opening formed substantially at a centered area of the coil holder, the base opening being sufficiently sized to provide a passage way to the inner opening of the core, and (i) a plurality of snap fit fingers extending from the base portion.
- 11. The method according to claim 10 further including:inserting the step portion of the cylindrical ferrite core into the snap fit fingers of the coil holder, whereby the core is locked into engagement with the coil holder.
- 12. The method according to claim 7 wherein the first high dielectric material is a material different from the second high dielectric material.
- 13. The method according to claim 7 wherein the steps of applying the first and second high dielectric materials include at least one of coating, spraying, dripping and brushing.
- 14. A method of assembling a coil which includes a core having a top end, a bottom end, an inner opening extending from the top end to the bottom end, and a cylindrical outer surface, the method comprising:applying a first high dielectric material onto the outer surface of the core; winding a conductive wire onto the first high dielectric material; applying a second high dielectric material over the conductive wire; curing the first high dielectric material and the second high dielectric material into a single solid mass, wherein the conductive wire is held in a fixed position; inserting the core into a coil holder, the coil holder including a base portion with a base opening, the base opening being sufficiently sized to provide a passage way to the inner opening of the core.
- 15. The method according to claim 14 wherein the first high dielectric material is a material different from the second high dielectric material.
- 16. The method according to claim 15 wherein,the step of applying the first high dielectric material further includes applying the first high dielectric material in a partially cured state such that the first high dielectric material has a tacky compliant quality; the step of winding the conductive wire onto the partially cured first high dielectric material including embedding at least a portion of the conductive wire into the partially cured high dielectric material, thereby holding the wound conductive wire in a secure position; and the step of curing includes forming a hermetic seal around the conductive wire.
- 17. The method according to claim 14 wherein the steps of applying the first and second high dielectric materials include at least one of coating, spraying, dripping and brushing.
- 18. The method according to claim 14 wherein the step of inserting includes inserting a step portion into snap fit fingers of the coil holder.
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Number |
Name |
Date |
Kind |
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Jan 1972 |
A |
4978712 |
Bair et al. |
Dec 1990 |
A |
5600294 |
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Feb 1997 |
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Number |
Date |
Country |
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JP |