Information
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Patent Grant
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6342778
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Patent Number
6,342,778
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Date Filed
Thursday, April 20, 200024 years ago
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Date Issued
Tuesday, January 29, 200222 years ago
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CPC
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US Classifications
Field of Search
US
- 323 224
- 323 220
- 336 200
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International Classifications
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Abstract
A low-profile, surface mount magnetic component is described along with magnetic devices and power supplies using the magnetic components. The magnetic component is formed from a magnetic core which is surrounded by a plurality of conductive elements. The conductive elements fit into channels in the sides of the magnetic core, the channels having angled sides that increase in width from the top to the bottom. The conductive elements have their ends bent inwards against the bottom of the magnetic core to form surface mountable contact surfaces. A recess in the top of the magnetic core allows the conductive elements to be loaded before the ends are bent inward so that when the conductive elements are unloaded they fit tightly against the magnetic core and the conductive surfaces are coplanar.
Description
TECHNICAL FIELD OF THE INVENTION
The invention relates to magnetic devices such as inductors and transformers. Specifically, the invention relates to magnetic devices that can be assembled as low profile surface mount devices on a printed circuit board or a metallized substrate.
BACKGROUND OF THE INVENTION
Magnetic devices, such as inductors and transformers, are employed in many different types of electrical devices including communications equipment and power supplies. In practice, most magnetic devices are fabricated of one or more windings, formed by an elongated electrical conductor, such as a wire of circular or rectangular cross-section, or a planar electrical conductor wound about or mounted to a bobbin composed of a dielectric material, such as plastic. In some instances, the electrical member is soldered to terminations on the bobbin. Alternatively, the electrical member may be threaded through the bobbin for connection directly to a metallized area of an underlying circuit board. A magnetic core may be disposed about the bobbin to impart a greater reactance to the magnetic device and thereby alter its operating characteristics. The use of a bobbin, however, generally results in a magnetic device with a large profile, which not only takes up valuable space on the circuit board, but also results in a large height for the overall electrical device.
In addition to being formed with bobbins, magnetic devices can be formed with a magnetic core, such as ferrite or iron, wound with conductive coils. These devices are sometimes referred to as wire-wound core devices. One major difficulty with wire-wound core devices is that they have been difficult to miniaturize. While components such as resistors, diodes, capacitors and transistors have been drastically reduced in size, magnetics, including bobbin and wire-wound core devices, remain bulky.
One attempt at a low profile magnetic device is described in U.S. Pat. No. 5,574,420 issued Nov. 12, 1996 to Roy et al. The device described in Roy et al. is a magnetic component formed by a plurality of conductive elements surrounding a magnetic core. The conductive elements pass through holes or channels in the magnetic core and then are bent outwards to allow surface mount connection to a printed wiring board or the equivalent. Unfortunately, the magnetic component described by Roy et al. suffers from a number of deficiencies. First, the device is incapable of carrying large amounts of current because the small area of the magnetic core that is surrounded by the conductive elements tends to saturate quickly. Second, the bent out ends of the conductive elements make poor surface mount conductors because they are very difficult to make coplanar. Finally, the magnetic components of Roy et al. can be difficult to manufacture due to the shape of the magnetic core and the arrangement of the conductive elements.
Accordingly, what is needed is a low profile magnetic component that is capable of handling larger currents, has more consistently coplanar conductor elements, and is more easily manufactured.
SUMMARY OF THE INVENTION
Embodiments of the invention include providing for a low profile magnetic component formed from a magnetic core and a plurality of conductive elements, also referred to as conductors. The magnetic core includes a bottom, a top, end surfaces and side surfaces. The side surfaces include portions that are angled inward from the bottom to the top thereby forming a plurality of channels. The magnetic core further includes a recess in the top adjacent to the channels.
The plurality of conductors surround the magnetic core and pass through a corresponding channel from the plurality of channels. The top of the conductors are adjacent to the recess in the magnetic core and the ends are bent inward against the bottom of the core. The ends of the conductors form contact surfaces which are coplanar and surface mountable. In order to form the conductors tightly around the magnetic core and to ensure that the contact surfaces formed by the ends are coplanar, during manufacture the tops of the conductors are loaded causing the ends to bend inward in to the recess in the magnetic core. While the conductors are loaded the ends are bent inward toward the center of the bottom. After bending, the conductors are unloaded and the spring tension in the conductors causes them to fit tightly around the magnetic core and causes the ends to fit snugly against the base.
The magnetic components can be formed into a magnetic device such as an inductor by placing two or more in close proximity and using conductive traces on a printed wiring board or other insulated substrate to form the conductors into windings. This magnetic device can then be utilized in a power supply as, for example, the inductor in an output filter or as transformers in groups of two or more.
The foregoing has outlined, rather broadly, preferred and alternative features of embodiments of the invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
FIG. 1
is a perspective view of a low profile magnetic component according to a conventional arrangement;
FIG. 2
a
is a perspective view of a low profile magnetic component according to an embodiment of the invention;
FIG. 2
b
is a cross-sectional view of the magnetic component from
FIG. 2
a;
FIG. 3
is plan view of a magnetic device formed from an insulating substrate with conductive traces and two of the magnetic components from
FIG. 2
;
FIG. 4
is a circuit diagram showing a power supply incorporating the magnetic device from
FIG. 3
; and
FIG. 5
is a flow chart describing a process for making a low profile magnetic device in accordance with the principles of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to
FIG. 1
, a conventional surface mount magnetic component
10
is shown. Magnetic component
10
is formed by body
11
of magnetic material that is surrounded by a plurality of conductive elements
12
distributed along the major dimension of body
11
. Each conductive element
12
is formed with four right angle bends, the first and second bends allowing conductive element
12
to pass through channels
16
to surround a portion of the body, and the third and fourth bends to form a pair of contact surfaces
14
. Magnetic component
10
, however suffers from a variety of drawbacks. First, by having conductive elements
12
pass at right angles through channels
16
, a large portion of the cross-section of body
11
is not surrounded by conductive elements
12
. By limiting the cross-section of body
11
surrounded by conductive elements
12
, the magnetic flux able to be carried by body
11
is limited. Next, the third and fourth bends that form contact surfaces
14
are formed by bending conductive element
12
outward in free space. By forming contact surfaces
14
in this manner making them coplanar for surface mounting within specific tolerances is very difficult. Finally, magnetic component
10
is manufactured by taking the preformed conductive elements and placing them around body
11
. This type of manufacturing is difficult and only exacerbates the problem of trying to make contact surfaces
14
for all conductive elements
12
coplanar. If one conductive element
12
is misplaced by as little as a few thousands of an inch the coplanarity of the entire device is unacceptable.
In order to overcome these limitations a low-profile magnetic component is needed that a) uses as much of the cross-section of the magnetic core as possible, b) has conductive elements with contact surfaces that are tightly coplanar, and c) is easy to manufacture within design tolerances.
Referring now to
FIGS. 2
a
and
2
b
, a magnetic component according to an embodiment of the invention is shown. Low-profile magnetic component
20
shown in
FIGS. 2
a
and
2
b
is formed from magnetic core
22
and a plurality of conductive elements
24
. Magnetic core
22
typically is rectangular in shape, having a length l greater than the width w and height h. Conductive elements
24
are located in a center section
26
along the length l of magnetic core
22
. Center section
26
contains a number of features to accommodate conductive elements
24
, including recess
28
in the top
34
of magnetic core
22
, and channels
30
, which further include angled side surfaces
32
. Angled side surfaces
32
form a cross section that increases from top
34
to some distance above bottom
36
of magnetic core
22
. The angled side surfaces allow for better inspection capability of the assembled component. Wrapping the conductive elements
24
around the outside of magnetic core
22
allows more cross-sectional area to be surrounded by conductive elements
24
. This greater crosssectional area increases the amount of flux that can be handled by the core before saturation, and therefore, increases the amount of current that the magnetic device can accommodate.
Conductive elements
24
are also formed with coplanar contact surfaces
38
. Unlike magnetic device
10
from
FIG. 1
, contact surfaces
38
are formed by bending conductive elements
24
inward against the bottom
36
of magnetic core
22
. Bending conductive elements
24
inward to form contact surfaces
38
allows for much greater control over the coplanarity of the contact surfaces. Bottom
36
of magnetic core
22
is used as a stop to ensure consistent coplanarity both between contact surfaces
38
of a specific conductive element
24
as well as between contact surfaces
38
of different conductive elements
24
. Recess
28
, in top
34
of magnetic core
22
, aids in the formation of contact surfaces
38
. During manufacture, the top of conductive element
24
is displaced into recess
28
before it is bent to form contact surfaces
38
. After contact surfaces
38
are bent into place, the top of conductive element
24
is unloaded releasing the spring tension, which causes contact surfaces
38
to curl tightly up against bottom
36
of magnetic core
22
. Use of this loading of conductive element
24
allows a much more consistent formation of contact surfaces
38
which result in very coplanar surface mount contacts. The loading technique also allows conductive elements
24
to fit more tightly around magnetic core
22
to limit any potential movement of the conductive elements
24
.
A magnetic device is formed from magnetic component
22
by mounting two or more devices in close proximity on an insulating substrate having conductive traces for interconnecting the conductive elements of the magnetic component into windings.
FIG. 3
shows a magnetic device
40
formed from a pair of magnetic components
20
A and
20
B placed side by side to form an air gap
42
between them. Conductive trace
41
on an insulating substrate, such as printed wiring board
44
, is used to interconnect the conductive elements of magnetic devices
20
A and
20
B into windings. The magnetic components
20
A and
20
B, air gap
40
and conductive trace
41
together form a magnetic device
42
such as an inductor. Although magnetic device
40
is formed using two magnetic components, those skilled in the art would understand that similar magnetic devices could be formed using any number of magnetic components.
The inductor formed by magnetic device
40
from
FIG. 3
is suitable as a magnetic element in a power supply module. The circuit for such a power supply module
50
is shown in FIG.
4
. Power supply module
50
is formed by buck converter
52
with input voltage
54
, power switches
56
, output filter
58
and regulated output voltage
60
. Inductor
62
in output filter
58
is formed from magnetic device
40
from FIG.
3
. The operation of buck converter
50
is well understood in the art and will not be discussed further. Although the magnetic device is shown with reference to a buck-type converter, those skilled in the art would understand that the magnetic device according to embodiments of the invention is suitable for use in any type power supply which utilizes magnetic devices, particularly inductors.
Referring now to
FIG. 5
, a flow chart is shown that generally describes the manufacturing process
60
for making a magnetic component
20
from
FIGS. 2
a
and
2
b
according to embodiments of the invention. Manufacturing process
60
begins at step
62
by cutting conductive elements
24
to the required length from a continuous supply of conductive material. Once the conductors are cut to length, the process proceeds to step
64
where the conductors are preformed by bending them into a u-shape such that they will fit around the magnetic core
22
. Step
66
then requires that the conductors be placed around magnetic core
22
. In step
68
the tops of the conductors are loaded forcing them down slightly into recess
28
as was described with reference to
FIGS. 2
a
and
2
b
. The process then proceeds to step
70
where the ends of the conductors are bent inward against the bottom
36
of magnetic core
22
to form contact surfaces
38
. Finally the tops of conductors, or conductive elements
24
, are unloaded allowing the conductors to fit snugly to the magnetic core
22
and allowing contact surfaces
38
to form coplanar surfaces for surface mounting.
Typically, the embodiment magnetic core
22
is a ferrite material. For example, the conductive elements
24
are formed from copper, which is coated for solderability. Although particular references have been made to specific structures, topologies and materials, those skilled in the art should understand that magnetic component
20
could be formed in a multitude of materials and in a multitude of shapes and sizes, all of which are well within the broad scope of the invention.
Although embodiments of the invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.
Claims
- 1. A low profile power supply module for converting an input to a regulated output comprising:a printed wiring board; at least one power semiconductor device connected to the printed wiring board and operable to allow power to flow from the input to the regulated output; and an output filter electrically connected to the printed wiring board and operable to provide a stable voltage at the output, the output filter including an inductor which is formed from at least two low profile magnetic devices, each of the low profile magnetic devices further comprising: a magnetic core having a top, a bottom, two long sides, and two short sides, wherein the two long sides include a plurality of channels formed at an angle from near the bottom to the top; and a plurality of conductors surrounding the magnetic core and electrically connected to the printed wiring board, wherein a portion of the conductors is in a corresponding channel from the plurality of channels, and wherein the ends of the plurality of conductors are bent inward adjacent to the bottom of the magnetic core.
- 2. The power supply module of claim 1 wherein the power supply is a board mountable dc-to-dc power supply module.
- 3. The power supply module of claim 1 the magnetic core includes a recess in the top.
- 4. The power supply module of claim 3 wherein the recess allows the conductors to be loaded during manufacture, thereby allowing the ends of the conductors to be fit tightly against the bottom of the magnetic core.
- 5. The power supply module of claim 1 wherein the plurality of conductors includes four conductors.
US Referenced Citations (3)