U.S. patent number RE33,345 [Application Number 07/068,633] was granted by the patent office on 1990-09-18 for toroid transformers and secondary windings.
This patent grant is currently assigned to GFS Manufacturing Company, Inc.. Invention is credited to Vincent J. Bober, Paul C. Horn, Robert D. Sylvester, Jr..
United States Patent |
RE33,345 |
Sylvester, Jr. , et
al. |
September 18, 1990 |
Toroid transformers and secondary windings
Abstract
Secondary winding configurations and methods particularly
applicable for toroid transformers are described for winding
secondary windings over the indexed primary winding and toroidal
core. The secondary winding is formed in the configuration of a
multifilar winding of a plurality of coplanar parallel filaments
with a first elongate strip of electrically insulating material
bonded to the filaments on one side and a second elongate strip of
electrically insulating material bonded to the filaments on the
other side and to the first elongate strip. The resulting
electrically insulated multifilar strap winding contains the
filaments in substantially parallel coplanar relationship. The
mulfifilar strap winding is wound around the toroidal core in
substantially equally spaced turns. The strap winding maintains the
filaments substantially in equally spaced relationship relative to
each other over irregular surfaces and compound curvature of the
toroidal core without crossover. Mutual inductance between the
secondary winding of the invention and the primary winding is
optimized while leakage inductance is minimized. The invention is
applicable for high frequency switching transformers used in the
power supplies of microprocessors and computer accessories where
losses and spikes from leakage reactance must be minimized.
Inventors: |
Sylvester, Jr.; Robert D.
(Dover, NH), Horn; Paul C. (Somersworth, NH), Bober;
Vincent J. (Rochester, NH) |
Assignee: |
GFS Manufacturing Company, Inc.
(Dover, NH)
|
Family
ID: |
26749182 |
Appl.
No.: |
07/068,633 |
Filed: |
June 30, 1987 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
707135 |
Mar 1, 1985 |
04631511 |
Dec 23, 1986 |
|
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Current U.S.
Class: |
336/180; 336/186;
336/205; 336/226; 336/229 |
Current CPC
Class: |
H01F
27/2823 (20130101); H01F 27/2895 (20130101); H01F
30/16 (20130101) |
Current International
Class: |
H01F
30/06 (20060101); H01F 30/16 (20060101); H01F
27/28 (20060101); H01F 027/28 () |
Field of
Search: |
;336/229,222,205,206,200,223,170,180,186 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1044342 |
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Dec 1978 |
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CA |
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2541871 |
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Mar 1977 |
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DE |
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2602668 |
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Jul 1977 |
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DE |
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580898 |
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Nov 1924 |
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FR |
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77117 |
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Jun 1980 |
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JP |
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52117 |
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Mar 1982 |
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JP |
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190008 |
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Nov 1983 |
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JP |
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149503 |
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Nov 1962 |
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SU |
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221594 |
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Sep 1924 |
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GB |
|
674108 |
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Jun 1952 |
|
GB |
|
918978 |
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Feb 1963 |
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GB |
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Primary Examiner: Kozma; Thomas J.
Attorney, Agent or Firm: Kane, Jr.; Daniel H.
Claims
We claim:
1. A toroid transformer having a primary winding with indexed turns
distributed evenly around a toroidal core of permeable material and
a plurality of separate multifilar secondary windings formed in
separate layers over the indexed primary winding and around the
toroidal core where the toroid transformer is characterized by a
relatively high ratio of primary winding turns to secondary winding
turns of approximately at least 6 and the secondary windings are
formed over the compound curvature and irregular surface layers of
the toroid transformer comprising:
a plurality of layers of electrically insulating tape formed over
the primary winding around the toroidal core, each layer comprising
successive overlapping turns of tape of elongate strip
configuration, each turn lapping adjacent turns thereby increasing
distance over material surfaces between layers;
a multifilar first secondary strap winding formed over the indexed
turns of the primary winding and layers of electrically insulating
tape in substantially equally spaced turns around the toroidal
core, said first secondary strap winding comprising a flat array of
a plurality of coplanar parallel secondary winding filaments
electrically coupled in parallel, a first elongate strip of
electrically insulating tape having an adhesive layer on one side
adhesively bonded to one side of the multiple filaments, and a
second elongate strip of electrically insulating tape having an
adhesive layer on one side adhesively bonded to the other side of
the filaments and to the first elongate strip, said first and
second elongate strips being wider than the flat array of multiple
filaments thereby forming a margin of two strips of adhesively
bonded tape along the sides of the first secondary strap winding
extending beyond the outside filaments of the first secondary strap
winding thereby increasing distance over material surfaces between
separate winding layers, the filaments of the first secondary strap
winding being maintained in substantially equally spaced
relationship relative to each other without crossover and relative
to the turns of the primary winding over the compound curvature and
uneven surfaces of the layers around the toroidal core by the first
and second elongate strips adhesively bonded to each other and to
the multiple filaments of the first secondary strap winding thereby
optimizing mutual inductance between the first secondary strap
winding and the primary winding and minimizing leakage
inductance;
a second secondary strap winding formed directly over the first
secondary strap winding in substantially equally spaced turns
around the toroidal core without a separate electrically insulating
layer of tape between the first and second secondary strap
windings, said second secondary strap winding comprising a flay
array of a plurality of coplanar parallel secondary winding
filaments electrically coupled in parallel, a first elongate strip
of electrically insulating tape having an adhesive layer on one
side adhesively bonded to one side of the filaments, a second
elongate strip of electrically insulating tape having an adhesive
layer on one side adhesively bonded to the other side of the
filaments and to the first elongate strip, said first and second
elongate strips being wider than the flat array of multiple
filaments of the second secondary strap winding forming a margin of
two strips of adhesively bonded tape along the sides of the second
secondary strap winding extending beyond the outside filaments of
the second secondary strap winding thereby increasing distance over
material surfaces between separate winding layers, the multiple
filaments of the second secondary strap winding being maintained in
substantially equal spaced relationship relative to each other
without crossover and relative to the turns of the primary winding
over the compound curvature and uneven surfaces of the layers
around the toroidal core thereby optimizing mutual inductance
between the primary winding and the second secondary strap winding
and minimizing leakage inductance.
2. The toroid transformer of claim 1 wherein the multifilar first
secondary strap winding comprises a plurality of filaments spaced
apart from each other with substantially equal spacing between the
filaments.
3. The toroid transformer of claim 2 wherein the multifilar first
secondary strap winding comprises a quadrifilar winding.
4. The toroid transfromer of claim 1 further comprising a tertiary
winding comprising at least one filament, a first elongate strip of
electrically insulating tape having an adhesive layer on one side
adhesively bonded to one side of the filament and a second elongate
strip of electrically insulating tape having an adhesive layer on
one side adhesively bonded to the other side of the filament and to
the first elongate strip, said elongate strips being wider than the
filament forming a margin of two strips of adhesively bonded tape
along the sides of the tertiary strap winding extending beyond the
filament on each side thereby increasing distance over material
surfaces between separate winding layers, said tertiary winding
being formed directly over the indexed turns of the primary winding
in substantially equally spaced turns around the toroidal core
without a separate layer of electrically insulating tape being
formed between the primary winding and the tertiary winding.
5. The toroid transformer of claim 4 wherein the tertiary winding
comprises a single filament.
6. The toroid transformer of claim 5 further comprising a final
layer of electrically insulating tape formed over the multifilar
first and second secondary strap windings around the toroidal core,
said final layer comprising successive overlapping turns of
elongate strip configuration electrically insulating tape, each
turn lapping adjacent turns.
7. A toroid transformer having a primary winding with indexed turns
distributed substantially equally around a toroidal core of
permeable material and a plurality of separate multifilar secondary
windings formed in separate layers over the primary winding around
the toroidal core where the toroid transformer is characterized by
a relatively high ratio of primary winding turns to secondary
winding turns for each of the separate secondary windings and the
secondary windings are formed over the compound curvature and
irregular surface layers to the toroid transformer comprising:
a plurality of layers of electrically insulating tape of elongate
strip configuration formed over the primary winding, each layer
comprising successive overlapping turns of tap wrapped around the
toroid, each turn lapping adjacent turns thereby increasing
distance over material surfaces between the layers;
a multifilar first secondary strap winding formed over the primary
winding and layers of electrically insulating tape in substantially
equally spaced turns around the toroidal core, said first secondary
strap winding comprising a flat array of a plurality of coplanar
parallel secondary winding filaments electrically coupled in
parallel, a first elongate strip of electrically insulating tape
having an adhesive layer on one side adhesively bonded to one side
of the filaments, and a second elongate strip of electrically
insulating tape having an adhesive layer on one side adhesively
bonded to the other side of the filaments and to the first elongate
strap providing a unitary flat secondary strap winding, said first
and second elongate straps being wider than the flat array of
multiple filaments thereby forming a margin of two strips of
adhesively bonded tape along the sides of the first secondary strap
winding extending beyond the outside filaments of the first
secondary strap winding thereby increasing distance over material
surfaces between separate winding layers, the filaments of said
first secondary strap winding formed around the toroidal core being
maintained in substantially equally spaced relationship relative to
each other without crossover and to the indexed turns of the
primary winding over the compound curvature and irregular surfaces
of the toroid transformer by the first and second elongate strips
bonded to each other and to the filaments thereby optimizing mutual
inductance between the primary winding and first secondary winding
and minimizing leakage inductance;
a multifilar second secondary strap winding formed directly over
the first secondary strap winding in substantially equally spaced
turns around the toroidal core without a separate layer of
electrically insulating tape between the first and second secondary
strap windings, said second secondary strap winding also comprising
a flat array of a plurality of coplanar parallel secondary winding
filaments electrically coupled in parallel, a first elongate strip
of electrically insulating material tape having an adhesive layer
on one side adhesively bonded to one side of the filaments, and a
second elongate strip of electrically insulating tape having an
adhesive layer on one side adhesively bonded to the other side of
the filaments and to the first elongate strip forming a unitary a
flat second secondary strap winding, said first and second elongate
strips being wider than the flat array of multiple filaments
thereby forming a margin of two strips of adhesively bonded tape
along the sides of the second secondary strap winding extending
beyond the outside filaments of the second secondary strap winding
thereby increasing distance over material surfaces between separate
winding layers, the multiple filaments of the second secondary
strap winding formed over the first secondary strap winding around
the toroidal core being maintained substantially in equally spaced
relationship relative to each other without crossover and to the
indexed turns of the primary winding over the compound curvature
and irregular surface layers of the toroid transformer by the first
and second elongate strips of electrically insulating tape
adhesively bonded to each other and on each side of the filaments
thereby optimizing mutual inductance between the primary winding
and the second secondary strap winding and minimizing leakage
inductance;
and a tertiary strap winding comprising at least one filament, a
first elongate strip of electrically insulating tape having an
adhesive layer on one side adhesively bonded to one side of the
filament and a second elongate strip of electrically insulating
tape having an adhesive layer on one side adhesively bonded to the
other side of the filament and to the first elongate strip to
provide a unitary flat tertiary strap winding, said first and
second elongate strips being wider than the flat array of multiple
filaments thereby forming a margin of two strips of adhesively
bonded tape along the sides of the tertiary winding extending
beyond the outside filaments of the tertiary winding thereby
increasing distance over material surfaces between separate winding
layers, said tertiary strap winding being formed in substantially
equal turns directly over the indexed turns of the primary winding
without a separate layer of electrically insulating tape between
the primary winding and the tertiary strap winding.
8. The toroid transformer of claim 7 wherein said first secondary
strap winding comprise multiple filaments spaced apart from each
other with substantially equal spacing between the filaments.
.Iadd.
9. In a toroid transformer having an annular core of permeable
material about which radially is wound a toroidal primary winding,
and about which radially is wound at least one toroidal secondary
winding;
the improvement wherein at least the secondary winding comprises a
flat, multifilar strap which includes a plurality of filaments
arranged in substantially parallel, coplanar relationship, and
elongate strip means of electrically insulating material underlying
and overlying the plurality of filaments,
the flat, multifilar strap secondary winding providing for
maintaining the substantially parallel, coplanar relationship of
the filaments without crossover during radial toroidal winding
about curved or irregular toroid surfaces, and providing electrical
insulation between turns of the multifilar strap secondary winding
and between the secondary and primary windings. .Iaddend.
.Iadd.
10. The transformer of claim 9 wherein the elongate strip means of
electrically insulating material is adhered to the parallel,
coplanar filaments. .Iaddend. .Iadd.11. The transformer of claim 9
wherein the elongate strip means includes a first elongated strip
of electrically insulating material underlying and adhered to the
parallel, coplanar filaments, and a second elongated strip of
electrically insulating material overlying and adhered to the
filaments and to the first elongated strip. .Iaddend. .Iadd.12. The
transformer of claims 10 or 11 wherein the elongate strip means of
insulating material have an adhesive layer. .Iaddend. .Iadd.13. The
transformer of claims 9, 10, or 11 wherein there are plural winding
straps. .Iaddend. .Iadd.14. The transformer of claim 13 wherein at
least one of the winding straps is a flat strap having a single
filament. .Iaddend. .Iadd.15. The transformer of claim 9 further
including at least one further winding which comprises a flat strap
which includes at least one filament, and elongate strip means of
electrically insulating material underlying and overlying and
adhered to the at least one filament,
the further flat strap winding providing for radial toroidal
winding about curved or irregular toroid surfaces without
crossover, and providing electrical insulation between turns of the
further strap winding and
between the further winding and the other windings. .Iaddend.
.Iadd.16. In a toroid transformer having an annular core of
permeable material about which radially is wound a toroidal primary
winding, and about which radially is wound at least one toroidal
secondary winding and at least one tertiary winding;
the improvement wherein the at least one secondary winding
comprises a flat, multifilar strap winding which includes a
plurality of filaments arranged in substantially parallel, coplanar
relationship, and elongate strip means of electrically insulating
material underlying and overlying and adhered to the plurality of
filaments,
the flat, multifilar strap secondary winding providing for
maintaining the substantially parallel, coplanar relationship of
the filaments without crossover during radial toroidal winding
about curved or irregular toroid surfaces, and providing electrical
insulation between turns of the secondary winding and between the
secondary winding and other windings, and wherein
the at least one tertiary winding comprises a flat strap which
includes at least one filament, and elongate strip means of
electrically insulating material underlying and overlying and
adhered to the at least one filament to provide a strap winding for
radial toroidal winding about curved or irregular toroid surfaces
without crossover, and providing electrical insulation between
turns of the tertiary strap winding and between the tertiary
winding and the other windings.
Description
TECHNICAL FIELD
This invention relates to secondary winding configurations and
methods particularly applicable in toroid transformers such as high
frequency switching transformers used in switch mode power supplies
for microprocessors, computers, and accessories.
BACKGROUND ART
Transformers for power supplies in computers and accessories must
meet the demanding requirements of computing equipment for low
losses in the switching mode and elimination of spikes in the
output. Such losses typically result from leakage inductance and
consequent leakage reactance caused by irregular spacing of the
secondary windings relative to the primary windings. The leakage
inductance is inversely related to mutual inductance coupling
between the windings and results in a lower coefficient of coupling
between the windings. Manufacturers generally require very low
levels of leakage inductance. For example, the leakage inductance
specification for a power supply transformer used with
microprocessor computers and accessories is 45 microhenries (.mu.h)
maximum.
This low specification for leakage inductance is difficult to
achieve in toroid transformers with multiple secondary and tertiary
and windings with intermediate insulating layers wound over the
primary winding and toroidal core. The complex winding
configurations must frequently be wound and placed by hand. The
compound curvature of the core and the irregular surfaces produced
by the complex of windings and insulating layers make it difficult
to achieve regular and optimal spacing of the secondary windings
relative to the primary winding for maximizing mutual inductance
coupling.
Multifilar secondary windings are particularly prone to
irregularity in the spacing of the multiple filaments on toroid
transformers. The parallel filaments which comprise each turn of
the multifilar secondary are used to achieve greater distribution
and more even distribution of the secondary winding turns over the
primary winding and therefore greater mutual coupling. However,
irregularity and unevenness in the equal spacing of the parallel
filaments of the multifilar secondary winding and crossover of the
filaments interferes in the mutual inductance coupling and
increases leakage inductance. Such irregular spacing and crossover
of filaments is a particular problem on toroidal cores and in
toroid transformers because of the irregular surfaces over which
the multifilar secondaries must be wound, often by hand.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide new
multifilar secondary windings, configurations, and methods
particularly applicable for toroid transformers which maintain
substantially even spacing between the filaments of the multifilar
winding for minimizing leakage inductance and optimizing mutual
inductance coupling with the primary winding.
Another object of the invention is to provide toroid transformers
with secondary winding configurations and arrangements which
achieve and surpass leakage inductance specifications for computing
equipment transformer standards achieving leakage inductances as
low as 26 to 36 .mu.h as an example.
A further object of the invention is to provide new multifilars
secondary windings and methods which are adaptable to automated
manufacture and machine winding, which themselves function as
insulating layers on the transformer, and which eliminate some of
the winding steps typically implemented by hand in manufacturing
and winding high frequency switching toroid transformers.
DISCLOSURE OF THE INVENTION
In order to accomplish these results the present invention provides
a new secondary winding configuration particularly applicable for
toroid transformers and a new method for winding secondary windings
over the indexed primary winding and toroidal core. The invention
contemplates the method of forming the secondary winding in the
configuration of a multifilar winding of a plurality of coplanar
parallel filaments, bonding a first elongate strip of electrically
insulating material to the filaments on one side and bonding a
second elongate strip of electrically insulating material to the
filaments on the other side and to the first elongate strip to
provide an electrically insulated multifilar strap winding
containing the filaments in substantially parallel coplanar
relationship. The invention then provides the step of winding the
multifilar strap winding around the toroidal core in substantially
equally spaced turns.
A feature and advantage of this secondary winding configuration and
winding method is that the strap winding maintains the filaments
substantially in equally spaced relationship relative to each other
on the toroidal core without crossover. Mutual inductance between
the secondary winding of the invention and the primary winding is
optimized while leakage inductance is minimized. The invention is
therefore applicable for high frequency switching transformers used
in the power supplies of microprocessors and computer accessories
where losses and spikes from leakage reactance must be
minimized.
In a preferred example, the first and second elongate strips of
electrically insulating material are strips of tape formed with an
adhesive layer on one side and the strips of tape are adhesively
bonded to the filaments of the multifilar winding on either side
and to each other. For a multifilar winding of wide distribution
and spacing between the filaments, the adhesively bonded strips
maintain substantially equal spacing between adjacent filaments.
Alternatively, where the filaments are arranged adjacent to each
other in substantially contiguous relationship, the bonded strips
of the multifilar strap winding nevertheless maintain the filaments
in substantially parallel coplanar relationship without
crossover.
A number of secondary and tertiary strap windings, according to the
invention, are described such as trifilar and quadrifilar strap
windings. A feature and advantage of the insulated laminating
tertiary and secondary strap windings is that new toroid
transformer configurations are provided meeting demanding
specifications for low leakage flux, leakage induction, and leakage
reactance along with a new simplified method for winding the toroid
transformer which eliminates a number of the conventional winding
steps.
For example, according to the method of the present invention a
number of conventional insulation winding steps for adding
insulating layers required between windings are eliminated. The new
secondary strap winding itself incorporates insulating layers on
either side of the multifilar filaments and the strap itself
functions as an insulating layer on the transformer.
Other objects, features and advantages of the invention are set
forth in the following specification and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is plan view of a quadrifilar secondary strap winding
according to the present invention.
FIG. 2 is another plan view of the quadrifilar secondary strap
winding with the overlapping back strip of electrically insulating
tape cut away exposing the filament leads.
FIG. 3 is a plan view of the quadrifilar secondary strap winding of
FIG. 2 with color coded tubing inserted over the filaments.
FIG. 4 is a plan view of the quadrifilar secondary strap winding of
FIG. 3 ready for winding around the toroidal core of a transformer
with wrap around tape holding the color coded tubing in place.
FIG. 5 is a plan view of a trifilar secondary strap winding
according to the invention.
FIG. 6 is a plan view of the trifilar secondary strap winding of
FIG. 5 with the overlapping back strip of electrically insulating
tape cut away exposing the filaments.
FIG. 7 is a plan view of a monofilament strap winding according to
the invention suitable for use, for example as a tertiary winding
on a toroid transformer.
FIG. 8 is a plan view of the monofilament tertiary strap winding of
FIG. 7 with color coded tubing in place over the ends of the
filament and with the overlapping back strip of electrically
insulating tape cut for folding over and wrapping to hold the color
coded tubing in place.
FIG. 9 is a perspective view of a conventional toroidal core with
an indexed primary winding in place on the core.
FIG. 10 is a perspective view of a tertiary secondary strap winding
in place over the toroid transformer core and primary winding
according to the invention.
FIG. 11 is a perspective view of a completed layer of one of three
layers of insulating tape wrapped over the primary and tertiary
windings.
FIG. 12 is a diagrammatic view of the toroid transformer of FIG. 11
with the uneven surface of the insulating layers simplified to show
diagrammatically a smooth torus or donut and showing the first step
in winding a quadrifilar secondary strap winding of equally spaced
apart filaments around the toroid.
FIG. 13 is a perspective view of the toroid transformer of FIG. 12
showing a further step in winding the quadrifilar secondary strap
winding while
FIG. 14 is a perspective view of the toroid transformer with the
winding of the quadrifilar secondary strap winding in four equally
spaced turns around the torus completed.
FIG. 15 is a perspective view of the toroid transformer of FIG. 14
with a trifilar secondary strap winding wound in equally spaced
turns directly over the quadrifilar secondary strap winding,
according to the invention, without winding an intermediate layer
of electrically insulating tape.
FIG. 15A is a detailed fragmentary view of FIG. 15.
FIG. 16 is a detailed fragmentary view of the portion of the toroid
transformer showing the leads from the secondary strap windings and
the step of wrapping with a final single layer of electrically
insulating tape .
DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND BEST MODE OF THE
INVENTION
A quadrifilar secondary strap winding 10 provided by the invention
is illustrated in FIG. 1, consisting of four spaced apart but
equally spaced copper wires or filaments 12, a first strip or layer
of insulating tape 14 with an adhesive layer 14a facing and bonded
to the filaments 12, and a second strip or layer 16 of insulating
tape with an adhesive layer facing and bonded to the filaments and
to the first strip of insulating tape 14. The adhesive bonding of
the strips of insulating tape 14 and 16 to each other in the spaces
between the filaments 12 maintain and assures the equal spacing of
the filaments 12 relative to each other without crossover even on
irregular surfaces and surfaces of compound curvature as hereafter
described.
As shown in FIG. 1 the strap winding 10 is initially formed with
the first or back strip of insulating tape 14 overlapping and
extending beyond the second or front strip 16 to the full length of
the filaments 12 adhesively bonding to the filaments on one side.
By this arrangement the integrity and spacing of the filaments 12
is maintained during handling prior to final preparation. On the
other hand, the single strip 14 can be easily peeled back from the
filaments 12 and cut at the desired length, for example, a length
equal to the second or front strip 16 as shown in FIG. 2 in
preparation for receiving color coded insulating tubing 18 as
illustrated in FIG. 3 for lead identification. The color coded
tubing leads are held in place adjacent to the elongate strips of
insulating tape 14 and 16 by wraparound insulating tape 22 to
provide the completed quadrifilar secondary strap winding 20 as
illustrated in FIG. 4 ready for winding, for example, on a toroid
transformer as hereafter described.
A trifilar secondary strap winding 30, according to the invention,
is illustrated in FIG. 5. As shown in this example, the trifilar
winding is formed by three filaments 32 adjacent to each other in
substantially contiguous relationship with a first strip 34 of
insulating tape on one side of the filaments 32 with an adhesive
layer 3a facing and adhesively bonding to the filaments 32, and a
second elongate strip 36 of insulating tape on the other side or
front side of the filaments 32 with an adhesive layer facing and
adhesively bonding to the three adjacent contiguous filaments 32
and to the first strip of insulating tape 34 on either side of the
three filaments. The adhesive bonding of the strips of dielectric
or electrically insulating tape 34 and 36 to the filaments 32 and
to each other on either side of the filaments maintains the
filaments in coplanar parallel relationship without crossover for
winding on irregular surfaces as hereafter described.
The first strip or back strip 34 of insulating tape overlaps and
extends beyond the ends of the second strip of tape 36 to the full
length of the filaments 32. By this initial configuration, the
integrity and arrangement of the ends of the filaments are
maintained intact while subsequently permitting the overlapping
strip 34 to be peeled back and cut at a desired length, for
example, equal to the second strip or front strip 36 as shown in
FIG. 6 exposing the ends of the filaments 32 for leads. Thus, the
expedient, according to the invention, of using an overlapping
strip extending the full length of the filaments on one side as
shown in the examples of FIGS. 1 and 5 avoids the disadvantage
attendant upon extending both strips the full length of the
filaments where the adhesive bonding of the strips of tape to each
other would make it difficult to peel back and expose the ends of
the filaments for leads. While the single layer of overlapping tape
at the ends affords adequate protection, it also permits each
"peelback" for cutoff at a desired length to receive, for example,
color coded insulating tubing over the ends of the filaments as
shown in FIGS. 3 and 4 and as also maybe accomplished in a similar
manner over the ends of the filaments 32 in FIG. 6.
A single filament strap winding 40 useful, for example, as a
tertiary winding is shown in FIG. 7 and is formed with a single
copper wire or filament 42, a first strip or back strip 44 of
electrically insulating tape having an adhesive layer 44a facing
and adhesively bonding to the filament 42, and a second strip 46 of
electrically insulating tape on the other side with an adhesive
layer facing and adhesively bonding to the single filament 42 and
to the first strip 44 on either side thereby maintaining the
filament 42 in linear condition between the strips of tape. In the
example of FIG. 7 the first strip 44 along the back of filament 42
is initially cut or subsequently peeled back and cut to expose the
ends of the filament but still overlap and extend beyond the first
strip 46 so that the overlapping length 45 of the strip of tape 44
is available to wraparound and adhere to, for example, color coded
tubing 48 placed over the ends of the filament to retain the tubing
adjacent to the ends of the tape. In this example black PVC tubing
48 coaxially surrounds the inner color coded tubing 49.
The mulfilar secondary strap windings are filament wire sizes
typically used in transformer windings such as #20 or #22 copper
wire. For the strips of electrically insulating material, adhesive
tape of dielectric or insulating material may be used such as, for
example, #1298 Mylar (TM) tape or #10 Mylar (TM) tape, available
from 3M Company, having a width appropriate to the distribution and
spacing of the flat multifilar filaments in the strap. For example,
for a quadrifilar secondary strap winding such as illustrated in
FIG. 1-4, #1298 Mylar (TM) tape having a width of 1 inch (2.5 cm)
is appropriate. For a thinner strap such as the trifilar secondary
winding strap of FIGS. 5 and 6 a tape width of 1/4 inch (0.6 cm)
provides sufficient overlap on the sides. Alternatively, a
combination of different gauge tapes may be used such as #1298 tape
on one side and #10 tape on the other side. For the color coded
insulating tubing at the lead ends of the filaments, Teflon (TM)
tubing or PVC tubing are typically used. In the monofilament
tertiary strap winding illustrated in FIGS. 7 and 8 a tape wider
than the trifilar strap winding is used such as, for example, tape
of 3/8 inch (1 cm) to provide a wider insulating layer function and
retain the winding in place during wrapping.
A toroid transformer incorporating the new secondary winding
configuration and winding method is illustrated in FIGS. 9-16. As
shown in FIG. 9 the manufacturing steps or transformer winding
steps begin with a conventional torus or toroidal core 50 of
magnetically permeable material such as ceramic ferrite material
with indexed turns of primary winding 52 equally spaced around the
core 50. The primary winding 52 is typically machine wound and in
this example is formed by 80 indexed turns. The leads 54 and 55 of
the primary winding are color coded for lead identification with,
for example, yellow electrically insulating tubing 56 such as
Teflon (TM) tubing and white Teflon (TM) tubing 57 respectively as
shown in FIG. 10. The yellow and white tubing 56 and 57
respectively are in turn covered by black tubing 58 such as black
PVC tubing to meet lead wire specifications. Typically, #19 tubing
is used for the color coded inner yellow tube 56 and white tube 57
while a shorter length of 190 13 tubing coaxially slides over the
inner tubing.
Five turns of a tertiary winding 60 are wound equally spaced around
the primary winding 52 using a monofilament strap winding 40 of the
type illustrated in FIG. 7. In this example the leads 62 and 63 of
the monofilament tertiary strap winding 40 are color coded with
black inner tubing 64 and blue inner tubing 67 respectively with
further lead protection provided by black PVC outer tubing 66.
The tertiary winding 60 is included in the transformer for sensing
the voltage output and pulse width on the primary winding 52 and is
typically hand wound. The monofilament strap winding configuration
40 according to the invention facilitates equal spacing and
distribution of tertiary winding around the toroid and at the same
time provides insulating layers on either side of the monofilament,
between the monofilament and adjacent underlying and overlying
windings. The step of winding a separate layer in insulating tape
between the primary and tertiary windings is therefore
eliminated.
Computing equipment standards then typically require several
insulating layers 65 over the primary winding before adding the
secondary windings. The insulating layers 65 are typically provided
by wrapping several layers of insulating tape 68 around the torus
appropriately positioning the respective lead wires 54, 55, and 62,
63 during the wrapping of each layer, lapping the tape over
successive laps and the tubing of the lead wires in a prescribed
manner in each instance.
In FIG. 12 the partially completed torus and insulating layer 65
which is actually a cylindrical toroid is shown diagrammatically as
a smooth annulus or donut in FIGS. 12-14 for clarity in
illustrating the steps of wrapping or winding the first multifilar
secondary strap winding 70. The strap winding 70 is in the same
configuration as the quadrifilar strap winding 10 of FIGS. 1-4 with
sufficient length to provide four complete turns around the torus.
As heretofore described the filaments 72 of quadrifilar strap
winding 70 are spaced apart and distributed with equal spacing
between the filaments to optimize mutual coupling between the
secondary winding 70 and primary winding 52 by better distribution
of each turn of the secondary winding 70 over the toroid. As shown
in FIGS. 13 and 14, the four turns of the flat quadrifilar
secondary strap winding 70 are wrapped around the toroid with equal
spacing between the turns placing the leads of the filaments 72 and
color coded lead filament tubing 18 at the desired position on the
toroid relative to the leads 62 and 63 of the monofilament tertiary
strap winding 40 and leads 54 and 55 of the primary winding 52.
The first secondary strap winding 10 with 4 turns of the parallel
filaments distributed over the 80 turns of the primary winding
provides a turn ratio of 1 to 20. With standard line voltage, e.g.
110 volts, applied to the primary winding, the first secondary
winding 10 provides the 5 volt power supply leads.
A feature and advantage of the multifilar secondary strap winding
configuration and method according to the invention is that the
laminar construction of the insulating strips and intermediate
filaments maintains the filaments with substantially uniform and
equal spacing over the toroid relative to the primary winding and
in particular the turns of the primary winding. Thus, while there
is greater spacing between the 80 turns of the primary winding on
the outside of the toroidal core and closer spacing on the inside,
the spacing between the indexed cores is substantially the same at
any particular circular cross-section. Similarly, the secondary
strap winding configuration 70, according to the invention, at each
turn around the toroid maintains the filaments with substantially
equal spacing relative to each other with greater spacing at the
outside of the torus and closer spacing on the inside but with a
complementary uniformity relative to the primary turns. This
conformational wrapping of the secondary strap winding relative to
the primary winding afforded by the present invention optimizes
mutual inductance between the primary and secondary winding and
minimizes leakage inductance and losses from consequent leakage
reactance. The conformational uniformity is attributable to the
secondary winding configuration and method, according to the
present invention, for exceeding the most demanding tolerances for
low leakage flux, leakage inductance and leakage reactance.
Another feature and advantage of the strap winding method according
to the present invention is that time consuming and labor intensive
steps in the manufacture of the toroid transformer are eliminated.
For example, as shown in FIG. 10 the tertiary sensor filament with
insulating layers on either side is wrapped or wound in a single
step thereby eliminating the prior art step of wrapping an
insulating layer such as a layer of tape around the primary beneath
the tertiary winding and before placement of the tertiary winding.
Because this is typically a manual winding step, there is
substantially savings in labor intensive time and expense.
Similarly, upon completion of winding of the first secondary strap
winding 70, a second secondary strap winding 80 may be placed
directly over the first secondary winding as shown in FIG. 15.
According to the present invention, the strap windings function not
only as filament windings but also at the same time constitute
insulating layers on either side of the filaments. While the
laminar strips such as insulating tape on either side maintain the
filaments in optimal uniform conformations relative to the primary
winding for minimizing leakage inductance and reactance, the
insulating strips at the same time can eliminate manual winding
steps by delivering insulating layers in place with the
filaments.
As shown in FIG. 15, a second secondary winding 80, for example in
the configuration of the trifilar secondary strap winding 30 of
FIGS. 5 and 6 is wound or wrapped in twelve equally spaced turns
around the torus and over the first secondary winding 70 with the
trifilar filament leads 32 placed in the desired position relative
to the leads of the other windings. A final insulating layer is
then wrapped or wound over the second secondary using, for example,
#20 insulating tape and the tape 68 is wrapped in a prescribed
manner with overlapping, etc. for placement of the lends of the
lead wire in a desired configuration as shown in FIG. 16.
The second secondary strap winding 30 with 12 turns of the parallel
filaments distributed over the 80 turns of the primary winding
provides a turn ratio of 0:6.6. With standard line voltage applied
to the primary winding, the second secondary strap winding 30
provides the 16 volt power supply leads.
While the invention has been described with reference to particular
example embodiments, it is intended to cover all variations and
equivalents within the scope of the following claims.
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