Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
1998-05-11
2001-04-24
Gellner, Michael L. (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S083000
Reexamination Certificate
active
06222437
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to low profile surface mounted magnetic components and, more particularly, to magnetic components which include windings defined by a folded sheet material blank. The invention further relates to a multiple output switching power supply incorporating such components.
Surface mounted magnetic components such as inductors and transformers have typically been constructed using conductive wire having a circular cross-section wound around a ferrite core. Components constructed in this manner are quite large relative to other surface mounted components, particularly in the height dimension, due to the large number of windings required and because of the size of the ferrite core. This is particularly the case in high power applications where it is necessary to use large diameter wire. Such components also generate a substantial amount of heat due to conductive loses which occur as a result of the large number of windings typically required for these components.
More recently, magnetic components having planar windings etched in a spiral format on a printed circuit board have been utilized. These components are compact and have a low profile due to the planar etched windings. However, the etched windings do not provide sufficient current carrying capability for high power applications.
Magnetic components including a plurality of stamped windings are known in the art. Due to the higher volume of copper provided by the stamped windings, such components are more suitable than components having etched windings for high power applications and are therefore useful in devices such as high current switching power supplies. However, each of the stamped windings must be individually connected by a lead frame to an associated connection pad on the PC board. The substantial number of solder connections that are required makes assembly of devices including such components both difficult and time consuming and also raises concerns regarding the reliability of these devices.
Accordingly, there is a need for low profile magnetic components which provide sufficient current carrying capability for high power applications and which have low leakage inductance, low conductive loses and reduced heat output. There is also a need for devices, such as switching power supplies, incorporating such components which having improved reliability and repeatability in manufacturing.
SUMMARY OF THE INVENTION
The present invention provides, in one aspect, a blank formed from conductive sheet material. The blank defines a continuous conductive path which includes two terminal ends and at least three loops disposed along the path. The blank is foldable at preselected folding locations on the path to position the loops in overlying relation to one another. The blank is formed, for example, by stamping, punching or cutting the blank from the sheet of conductive material, and the blank is preferably formed with the loops disposed alone the conductive path in substantially the same plane. The terminal ends provide means for electrically connecting the conductive path within an electrical circuit.
In the preferred embodiment, the conductive path defined by the blank comprises an alternating series of loops and connecting portions. The series includes a first pair of loops connected together by a first connecting portion and at least a third loop connected to the first pair of loops by a second connecting portion which extends between one of the loops in the first pair and the third loop. The loops and the connecting portions are disposed relative to one another such that when the blank is folded at the preselected folding locations, the first pair of loops and the third loop are positioned in overlying relation to one another.
The blank is used to form a multi-turn planar winding for a magnetic device such as, for example, an inductor or transformer. Since the sheet material blank defines a number of loops having a flat or planar profile, the loops or turns of the winding are positioned immediately adjacent to one another in a very close stacking arrangement when the blank is folded. This close stacking provides a winding which has a low overall volume and a low profile relative to conventional discrete inductors and transformers. The winding formed from the sheet material blank also provides a substantially higher volume or surface area of conductive material in each turn of the winding than is available in conventional wire or etched windings so as to provide a higher current carrying capacity relative to such conventional windings. This results in a winding that has fewer turns (reduced length) than would be required in conventional windings having equivalent current carrying capacity.
In a second aspect, the invention provides a planar magnetic device, which includes a planar multi-turn winding formed from the folded blank. The device further includes an inductive core magnetically coupled to the winding to form a closed magnetic loop, and means for electrically insulating the winding turns from one another and from the inductive core.
In one embodiment, the planar magnetic device is a transformer, wherein the loops define a planar multi-turn primary winding of the transformer, and the terminal ends provide means for electrically connecting the primary winding with an electrical circuit. The transformer further includes a second blank which defines a second continuous conductive path. The second conductive path includes two terminal ends and at least one loop. This loop defines a planar single-turn secondary winding of the transformer which is disposed within the device adjacent to the primary winding, and preferably between two consecutive turns of the primary winding. Means are also provided for insulating the turns of the primary winding from one another and from the single-turn secondary winding and for insulating all of the windings from the inductive core.
The above-described transformer provides enhanced electromagnetic coupling between the primary and secondary windings because the planar single-turn secondary winding is positioned directly adjacent to at least one, and preferably between two, of the turns of the planar primary winding in a close stacking arrangement. The close coupling between the primary and secondary planar windings reduces the leakage inductance of the device. The planar windings also provide the transformer with a low overall volume because of the close stacking arrangement and a low profile since the windings are patterned to fit the transformer core and substantially fully utilize the core window area. The increased current carrying capacity of the planar windings and their reduced length relative to conventional windings of similar current capacity results in lower conduction losses and higher thermal dissipation to prevent overheating than is typical of prior art transformers and other inductive devices which utilize conventional windings.
In yet another aspect, the present invention provides a switching power supply with at least one voltage output which includes the above-described transformer. The power supply includes a well-regulated split in voltage outputs in those instances where the power supply employs two or more voltage outputs. The transformer provides the power supply with increased power density and also permits higher switching frequencies and a reduced overall package size since, as noted above, the transformer is characterized by lower leakage inductance, lower conduction losses and higher thermal dissipation than is typical of prior art transformers.
Other advantages of the present invention will become apparent in view of the following detailed description and accompanying drawings.
REFERENCES:
patent: 2851765 (1958-09-01), Hanlet
patent: 2943966 (1960-07-01), Leno et al.
patent: 3002260 (1961-10-01), Shortt et al.
patent: 4423361 (1983-12-01), Stenudd et al.
patent: 4517540 (1985-05-01), McDougal
patent: 4613843 (1986-09-01), Esper
patent: 4651254 (1987-03-01), Brede et al.
patent: 4654571 (1987-
Godek Paul W.
Soto Louis A.
Cummings & Lockwood
Gellner Michael L.
Nguyen Tuyen
Nidec America Corporation
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