Inductor devices – Winding formed of plural coils
Patent
1999-03-03
2000-11-21
Gellner, Michael L.
Inductor devices
Winding formed of plural coils
336182, 336185, 336198, 336208, H01F 2728
Patent
active
061509140
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a transformer with a divided primary winding in an isolating transformer power supply circuit.
An article by Klaus Mock, "Transformatoren fur Schaltnetzteile" (Transformers for Switched-Mode Power Supply Units in Elektronik, No. 23, Nov. 16, 1993, pages 46-50 describes various transformers suitable for switched-mode power supply units for isolating transformers. In general, such transformers are widely used in consumer electronics because of their relatively simple design, even in the case of multiple output voltages. The essential functions of a transformer in a switched-mode power supply include transformation of one voltage into one or more other voltages and electrical isolation of multiple circuits. However, an actual transformer also produces a power loss which in turn leads to heating of core and winding in particular. The various windings are arranged on a bobbin which surrounds the magnetic core with the air gap contained therein. The ends of the individual windings lead to a number of terminal posts, where they are connected electrically and secured.
In the vicinity of the air gap, some of the magnetic flux does not pass through the cross-sectional area of the core but instead through the ambient air and the various windings, inducing eddy currents there. These often cause much greater losses than the skin effect and the proximity effect. The aforementioned article proposes a sandwich structure to reduce the leakage inductance in transformers of this type, wherein the primary winding is divided into two halves, and the secondary winding is enclosed between these two halves. This thus requires at least two, usually three main insulations, which are quite expensive.
With regard to specific applications of such transformers, e.g., in power supply circuits for high-pressure gas discharge lamps which are used preferentially in automotive headlights, the transformers known from the article cited above are not satisfactory because the losses are too high, the design is often very complex, and they have not been optimized to the demands of the power supply circuit.
SUMMARY OF THE INVENTION
The transformer according to the present invention with a divided primary winding has the advantage over the related art of especially close coupling of the primary winding and the load secondary winding with improved efficiency and the possibility of optimized tuning of core losses and winding losses so that no significant temperature gradient develops between core and winding. The transformer designed according to the present invention permits an optimized, simple and inexpensive design and thus favorable manufacturing. In addition, it can be adapted to a wide variety of application profiles.
According to the present invention, this is achieved in principle by dividing the primary winding into at least three partial windings; the secondary winding under the greatest power load for the longest period of time is divided into at least two partial windings; the partial windings of this load secondary winding are each enclosed by two partial windings of the at least three partial windings of the primary winding on the bobbin; and optionally one or more additional secondary windings are arranged outside the winding structure of the partial windings of the primary and load secondary windings.
In an especially exemplary embodiment according to the present invention, the at least three partial windings of the primary winding are connected in parallel externally. In a further exemplary embodiment according to the present invention, the at least two partial windings of the load secondary winding are connected in parallel internally.
According to a very advantageous exemplary embodiment of the present invention, no turns of the winding are provided in the area above the air gap. This greatly reduces the influence of the stray field there on the windings and also significantly decreases the eddy currents generated in the turns of the windings.
In an advantageous ememplar
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"Transformatoren fur Schaltnetzteile [Transformers for switched-mode power supply units]", Klaus Mock, Elektronik, Nov. 23, Nov. 16, 1993, pp. 46-50.**
Borho Lothar
Freundorfer Johann
Kern Robert
Gellner Michael L.
Mai Anh
Robert & Bosch GmbH
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