Inductor devices – With supporting and/or spacing means between coil and core – Preformed insulation between coil and core
Reexamination Certificate
2000-05-09
2002-06-11
Donovan, Lincoln (Department: 2832)
Inductor devices
With supporting and/or spacing means between coil and core
Preformed insulation between coil and core
C336S205000, C336S206000, C336S208000
Reexamination Certificate
active
06404316
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to magnetic devices, and, more specifically, to a magnetic device employing an isolation barrier and a method of manufacture therefor.
BACKGROUND OF THE INVENTION
Electronic manufacturers are constantly striving to make electronic components even smaller, especially in the field of magnetic devices. Miniature magnetic devices are used in a wide variety of electronic equipment such as telephones, televisions, computers, etc. With overall dimensions of the devices becoming smaller, the design of the magnetic devices presents unique challenges. The structure of the miniature devices must accommodate special features that are necessary to the manufacturability and electrical performance thereof.
A magnetic device is a device that uses magnetic material arranged in a defined structure for shaping and directing magnetic fields in a predetermined manner to achieve a desired electrical performance. The magnetic fields in turn act as the medium for storing, transferring and releasing electromagnetic energy. As a specific example of magnetic devices, transformers are composed of two or more windings wound about a bobbin with a magnetic core inserted through the bobbin. The bobbin may be made of virtually any suitable dielectric material. The insulated windings are wound about the bobbin in patterns to achieve specific electrical characteristics. The number of windings and the number of turns per winding is dictated by the function of the transformer in the intended circuit.
The bobbin may be manufactured separate from or integral with a base that provides the physical support for the bobbin. The transformer is electrically connected to the circuit by contacts extending from the base. A core of magnetic permeability, often ferrite, is inserted into the bobbin to shape the magnetic field. The core is often made in two pieces with an “E” shaped cross section. The central poles of the E-shaped core halves are inserted into opposite ends of the bobbin and the poles at the center of the bobbin. The complete transformer assembly is held together by various physical means such as an adhesive or spring clip.
Transformers work on the general principle that a change in current flowing through the primary winding, which is isolated from the secondary winding, creates a magnetic flux which causes a change in the current to flow in the secondary winding. The ratio of primary-to-secondary current is established by the number of windings in the secondary coil related to the number of windings in the primary coil. This, in turn, creates a voltage which is the product of the number of turns multiplied by the change in flux. This product is also proportional to a change in current multiplied by the inductance.
As the electronic devices employing magnetic devices continue to be made smaller, it is necessary to design a more compact and lower profile magnetic device (e.g., transformer). The limitation of “creepage,” however, can adversely affect the design and operation of the magnetic device. Creepage is generally defined as the transference of electrical current from one winding in a transformer to another winding in the same transformer by way of a conductive path forming a temporary bridge along a surface of a dielectric material separating the windings. The leakage current generally occurs as a result of ionization of air and insufficient creepage distance. Additionally, a minimum creepage distance is often required to comply with safety standards.
For example, a transformer may have a primary winding wound about a bobbin with a primary lead extending therefrom coupled to an input terminal of the transformer. In addition, the transformer may have a secondary winding wound concentrically about the same bobbin and around the primary winding. Although the primary winding and the secondary winding are separated by an insulator, the lead coming from the primary winding and terminating at the input terminal passes very close to the secondary winding. Because the primary lead passes very close to the secondary winding, there is the likelihood of creepage between the primary and secondary windings (e.g., at the point where the lead of the primary winding and the secondary winding are in the closest proximity to each other) thereby resulting in a potential short-circuit in the transformer. The distance between the point on the primary lead and the point on the secondary winding along the surface of which the creepage occurs is commonly known to those skilled in the art as the creepage distance.
As alluded to above, to help prevent creepage in magnetic devices, standards have been instituted defining minimum insulation permitted in a transformer. The standards are promulgated by administrative bodies such as the International Electrotechnical Commission (IEC) to, among other things, increase the safety of devices employing components such as magnetic devices (see, for instance, IEC Standard 60950, third edition, 1999). Included in these standards are the minimum creepage distances depending on the specifications of the transformer and the circuit into which the transformer is to be employed. The standards are becoming more universally accepted. Therefore, minimum creepage distance in magnetic devices is becoming a more important factor in the design of such devices.
In the prior art, two commonly employed methods are employed to assure a minimum creepage distance. The first method is to manufacture two separate bobbins, each one with a winding wound thereabout and leads affixed to the respective terminals. One bobbin is then placed inside of the other so that the leads of one winding and the other winding are isolated from each other. Although effective for ensuring a minimum creepage distance, the use of two bobbins has several disadvantages. First, the two-bobbin method requires the manufacture of two bobbins rather than only one, thus resulting in increased parts and manufacturing costs. Second, the use of two bobbins is better suited for larger transformers because of the difficulty associated with manufacturing miniature bobbins that fit together, one inside the other. Third, the use of one bobbin inside of another commonly leads to a large leakage inductance as a result of the space between the windings. Thus, the two bobbin approach is not the design of choice.
The second and more commonly employed method to assure a minimum creepage distance is the use of sleeves placed on the wire leads of the inner winding. However, like the two bobbin approach discussed above, the use of wire sleeves also has major disadvantages. Although the use of wire sleeves is employable in the manufacture of small transformers, placing the wire sleeves on each of the leads of the inner winding is a labor-intensive process that must be completed by hand. As a result, the costs of manufacturing small transformers having wire sleeves on the leads of the inner windings is high. In addition, although placing sleeves on the large leads of large transformers may appear at first glance to be a trivial task, placing sleeves on extremely small leads of miniature transformers becomes a tedious and time-consuming chore. As a result, labor costs, and thus the overall costs of manufacturing, are again elevated.
Accordingly, what is needed in the art is a magnetic device, and related method, that maintains a predetermined creepage distance therein, but overcomes the deficiencies of the prior art.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a magnetic device and a method of manufacture therefor. In one embodiment, the magnetic device includes: (1) a bobbin having a winding guide (or core tube) and molded-in margins proximate opposing inside flanges of the bobbin, each of the opposing inside flanges having at least one notch formed in an inside face of each of said opposing inside flanges; (2) an inner winding wound about the winding guide and between the molded-in margins; (3) an outer windin
Busletta Galliano R.
Catalano Robert J.
Offer, Jr. Paul J.
Wilkowski Matthew A.
Donovan Lincoln
Hitt Chwang & Gaines PC
Lucent Technologies - Inc.
Nguyen Tuyen T.
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