Patent Application
20090128276
The present application relates to the construction and configuration of an electrical inductor, where a powder is used to improve the heat dissipation properties of the inductor.
An electrical inductor typically comprises a series of electrical windings wrapped around a core material. The windings generate an electromagnetic field when current is applied. The properties of the inductor cause it to initially resist current as it builds up the electromagnetic field, and then allow current to pass once the electromagnetic field is in place. Inductors also store energy in the electromagnetic field resulting in a temporary continuation of current flow after any external current source is removed. These properties make inductors key elements in many circuit designs, including circuits with extremely high current frequencies. While operating at high current frequencies inductors typically generate high levels of heat and it can therefore become necessary to devise a way to remove the heat to prevent the inductor from being damaged. Inductors additionally can emit a high pitched tonal acoustic noise while operating at high frequencies.
It is known in the art to create electrical inductors with a potting material packed between the wire wound coils and the casing. The potting material provides a two-fold benefit. First the potting material can create a thermal path to draw heat away from the wire wound coil thereby providing more efficient heat dissipation, and second the potting material provides sound damping thereby reducing the high pitched tonal acoustic noise that can arise under certain circumstances.
Known potting materials are typically created by mixing a liquid matrix (such as epoxy) with a solid fill material. Potting material made in this way uses the thermal and electrical conductivity properties of the solid fill material to allow heat to be drawn away from the electrical windings of the inductor, without causing short circuits. The process used to create an inductor using potting material involves first mixing the fill material and the liquid matrix, pouring a first layer of the potting material into the assembled inductor, allowing the first layer to dry, and then applying additional layers as needed using the same process. Conventionally the maximum amount of the fill material does not typically exceed 70% of the overall mixture. Using conventional methods and potting materials, if the concentration of fill material in the potting material is too high then the potting material cannot be poured and the process described above cannot be performed.
Historically this method of assembling an inductor has had several associated drawbacks. A first drawback is that once the potting material application process is started the inductor cannot be reworked. As a result, any error in the potting material application or any defect in the potting material itself will cause the entire inductor to be scrapped. A second drawback is that the fill material is often unevenly distributed throughout the potting material, resulting in embedded air voids. This results in uneven heat dissipation as areas containing more fill material will be more efficient at conducting heat. A third drawback of this method is that the process of applying the potting material is relatively long and complicated, thus increasing costs and the possibility of defects.
Disclosed is an electrical inductor using at least one wire wound core. The inductor has at least one cavity adjacent to the wire wound core, and the cavity is at least partially filled by a powder.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
As illustrated in
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Powder 110 can be any powder that provides adequate thermal conductivity, as well as electrical resistivity. One example of a powder 110 that could meet the thermal and resistive requirements is a Boron Nitride powder. A powder meeting these characteristics enables a thermal path away from the wire wound core 10, while at the same time not enabling an electrical path connecting the windings 80 that could cause the windings 80 to short circuit. It is additionally possible to coat the powder particles with a micro-coating that reacts to heat, UV light, or other stimuli and creates an adhesive bond. This allows the powder to be placed in the inductor, and allows for reworking the inductor until the inductor is ready to be finalized. Then, a stimulus can be applied, bonding the powder particles together and holding the powder 110 in place. Using a micro-coating in this way makes use of a sealing layer above the powder unnecessary, as the adhesive nature of the micro-coating would hold the powder in place. Use of lightweight powder or powder with micro-coating results in a light weight potting compound.
The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
