Inductor devices – Winding with terminals – taps – or coil conductor end...
Reexamination Certificate
1999-05-13
2001-12-04
Donovan, Lincoln (Department: 2832)
Inductor devices
Winding with terminals, taps, or coil conductor end...
C336S198000, C336S208000
Reexamination Certificate
active
06326874
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to a terminal bobbin and, more specifically, to a terminal bobbin for a magnetic device and a method of manufacture therefor.
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 on 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.
As the electronic devices employing the magnetic devices continue to be made smaller, it is necessary to design a more compact and lower profile magnetic device. In conjunction therewith, the bobbin about which the magnetic device is constructed must also be made smaller. However, designing a miniature magnetic device about a miniature bobbin presents several problems.
First, the bobbin is usually made relatively thin in a region constituting the core of the device to minimize the electrical resistance of the conductor. Conversely, the remainder of the bobbin is usually made thicker to facilitate attachment of the electrical member to the bobbin terminals or to facilitate attachment of terminals on the bobbin to a circuit board. As a result of the need to make such a bobbin thinner in some regions and thicker in others, the bobbin is often subject to stresses at transition regions between such thinner and thicker regions.
Second, because of the need to maximize the number of winding turns while minimizing the winding resistance, the thickness of the electrical member Lorming each separate winding of the device is often varied. Variation in the winding thickness and the number of termination leads per terminal often result in a lack of coplanarity of the device terminations, an especially critical deficiency when the device is to be mounted onto a surface of a substantially planar circuit board. Also, it is often necessary to increase the number of series or parallel winding interfaces to increase the value of the coupling coefficient for the magnetic devices employed in higher frequency applications such as communications transformers. For very small devices with a few number of terminals, it is necessary to have more than one winding lead attached to the terminals of the bobbin. The process of coupling the winding leads to the terminals of the bobbin in such instances is obviously more complicated and tenuous with a miniature bobbin.
The problems associated with miniature bobbins are further magnified by the structure of the presently available bobbins. The terminals of the presently available bobbins principally serve dual roles. First, the terminals provide a location for attachment of the winding leads to the bobbin. Second, the very same terminals serve as a connector for the magnetic device to a circuit board of the electronic device. As the bobbin is miniaturized, it is not practical to employ the terminals in this fashion. Additionally, the presently available bobbins employ channels between adjacent terminals to assist in the placement of the winding leads to the terminals. The channels, however, force the adjacent winding leads to be located relatively close to one another. The resulting proximity of the winding leads is further aggravated as the bobbin is made smaller. The problem with not properly isolating the winding leads is that the electrical breakdown characteristic between windings will become pronounced. The breakdown characteristic may cause the windings of the adjacent terminals to short thereby causing a failure of the magnetic device.
Apart from the problems described above, the construction techniques necessary to manufacture such magnetic devices about the miniature bobbin are tedious. More particularly, the methods of wrapping and terminating the windings and mounting the core about the bobbin is arduous and subject to a high rate of failure. Also, the manufacturing processes for such magnetic devices tend to be laborious and costly, thereby making the present designs for the bobbin and magnetic devices unattractive.
Accordingly, what is needed in the art is a terminal bobbin that can accommodate the rigorous design criteria for magnetic devices while providing enhanced electrical characteristics and manufacturability for the magnetic devices.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a terminal bobbin, a magnetic device employing the terminal bobbin and a method of manufacturing therefor. The terminal bobbin includes: (1) a plurality of leads terminating in winding terminal portions; and (2) a bobbin formed about the plurality of leads, composed of a dielectric material and having a winding guide, the winding terminal portions spatially separated and the bobbin essentially free of guide channels thereby to allow windings terminating at the winding terminal portions to be spatially separated to enhance a breakdown characteristic between the windings, ends of the leads distal from the winding terminal portions extending from the bobbin to allow the terminal bobbin to be mounted to a substrate.
The present invention therefore improves upon the broad concept of employing a bobbin as a fixture device for holding the windings, thereby providing a compact terminal bobbin with a winding guide that facilitates spacial separation between adjacent windings. This allows the magnetic device to be compact, to assume a low profile and, by virtue of being free of guide channels, to be of high voltage breakdown capability (1500 volts between windings, for example). Further, the terminal bobbin provides leads that are configurable for multiple applications with enhanced rigidity and coplanarity for mounting to a substrate.
In one embodiment of the present invention, the leads are bent to form surface-mountable contacts for the magnetic device. In the embodiment to be illustrated and described, the leads are formed into “gull-wings,” which are angled toward the surface to which they are to be mounted. Of course, the leads may be through-hole formed or mounted in any other conventional or later-developed manner.
In one embodiment of the present invention, the winding terminal portions have a slot feature for receiving the windings thereon. When solder is applied to the windings on the winding terminal portions, the slot features distance the solder from the windings. Additionally, the winding terminal portions may be adapted to receive multiple winding ends. This allows variation in winding patterns, which are advantageous when the magnetic device is to handle high frequency electrical currents or higher current loads.
In one embodiment of the present invention, the bobbin has a core guide and an aperture formed therethrough adapted to receive a leg of a magnetic core. In this embodiment, the magnetic device forms an isolation transformer to provide electrical isolation for the circuit employing the transformer to advantage. OL course, other types of magnetic devices including, without limitation, non-isolation auto-transformer configurations are well within the broad scope of the present invention.
In one embodiment of the present invention, one of the ends of the leads includes a protrusion to orient the leads with respect to one another. The protrusion is a visible feature for the proper orientation of the bobbin during the manufacturing process. Of course, other pronounced features on the leads (such as a notch) to assist in or
Banzi, Jr. Frederick J.
Guancial Edward L.
Offer, Jr. Paul J.
Donovan Lincoln
Lucent Technologies - Inc.
Nguyen Tuyen T.
LandOfFree
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