JP2005064318A - Transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transformer which performs efficiently its heat radiation while reducing the noise leaked from a gap portion formed in its core. <P>SOLUTION: In the transformer wherein a gap portion 2 is formed in its core 1, and as the means for intercepting the noise radiated from the gap portion 2, it is so constituted by winding a short ring 3 around both its core 1 and bobbin 4 as to cover the gap portion 2 therewith, it is further so constituted by winding the short ring 3 a plurality of times that the short ring 3 functions as a heat radiating means too. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transformer used for a switching power supply of a copying machine or a printer.

2. Description of the Related Art Conventionally, in a transformer used for a switching power supply or the like, as shown in FIG. 2, a copper foil, an aluminum foil or the like is used to shield radiation noise due to leakage magnetic flux from a gap portion 12 formed in a magnetic core 11 (core). In many cases, the short ring 13 made of an electric conductor is wound around the gap portion 12. Here, the radiation noise emitted from the gap part 12 can be sufficiently shielded with a thin metal foil. Therefore, in the conventional transformer, the short ring 13 (for example, a copper foil tape having a width of 15 [mm] and a thickness of 0.035 [mm]) having the minimum necessary thickness is used as the magnetic core 11 from the viewpoint of lightening and cost reduction. And the bobbin 14 was wound only for one turn.
JP 2003-125584 A JP 2001-359280 A JP 2000-278936 A Japanese Patent Laid-Open No. 11-150030 Japanese Utility Model Publication No. 5-95023 Japanese Utility Model Publication No. 5-33515

  Certainly, the transformer having the above-described configuration can sufficiently shield the radiation noise from the gap portion 12 while minimizing the thickness and cost increase due to the short ring 13.

  However, in a transformer that does not include a short ring, even if the loss generated in the magnetic core becomes heat, the heat can be dissipated from the gap portion 12 to the surroundings. For example, when the coil temperature is 65 [° C.] with respect to the ambient temperature 25 [° C.], the transformer configured as described above can shield the radiation noise by the short ring 13, but the heat dissipation in the gap portion 12 is performed. As a result, the heat generated by the loss in the magnetic core 11 is trapped inside, resulting in excessive temperature rise of the transformer (for example, coil temperature 100 [° C.] with respect to ambient temperature 25 [° C.]). It was.

  Here, in the conventional transformer, as an improvement measure of the heat dissipation performance, an attempt has been made to increase the contact area with air by embossing the copper foil tape or the like used for the short ring 13. The amount of increase in the exchange area is only a slight amount, and the heat dissipation performance cannot be remarkably improved.

  Although it is possible to suppress the temperature rise of the transformer by increasing the cross-sectional area of the coil wound around the bobbin 14, in order to adopt such a configuration, the size of the magnetic core 11 must be increased. For transformers that are required to be small and light (for example, a small transformer for a switching power supply mounted on a circuit board), this is an inappropriate temperature measure.

  Patent Document 1 discloses a switching power supply in which electromagnetic wave noise radiated from the choke coil with a gap in the power factor correction circuit to the air is shielded from the filter circuit by a heat sink. Patent Document 2 discloses a power supply device in which some electronic components are arranged in an upper space of a transformer, and four sides of the transformer are surrounded by heat radiation means and a circuit board. In Patent Document 3, a noise generating electronic component is arranged in an internal space of a cylindrical substrate assembly formed by opening both ends of a combination of a plurality of substrates, and from a part of the electronic component. There is disclosed a switching power supply device in which a heat dissipating means for dissipating generated heat is disposed in the vicinity of the opening so as to face the internal space. Certainly, according to the conventional techniques of Patent Documents 1 to 3, it is possible to improve the heat dissipation efficiency while reducing noise leakage from the transformer to the outside. However, since all of the prior arts in Patent Documents 1 to 3 have a structure in which the transformer is shielded by a metal member to prevent noise leakage, there is a problem that the effect of the magnetic shield is reduced unless the transformer is sealed securely. It was. Moreover, since a large space is required for mounting the metal member surrounding the transformer, downsizing of the apparatus has been hindered.

  Patent Document 4 discloses a transformer in which the surface of the bobbin is shielded by a wire ring connected to the primary side ground. Certainly, with the prior art of Patent Document 4, it is possible to reduce noise leakage from the transformer. However, since the prior art of Patent Document 4 has a configuration in which a wiring shield is provided on a bobbin attached to a central magnetic leg of an E-type magnetic core, a transformer having a center gap structure (a gap portion is provided on the central magnetic leg of an E-type magnetic core). This is effective for a transformer, but has a problem that a transformer having a side gap structure (a transformer having a gap portion on a side magnetic leg of an E-type magnetic core) has no effect.

  Further, Patent Documents 5 and 6 disclose two end edges of the opening surface of the transformer case as a measure for preventing displacement of a conductor (short ring) wound around the transformer in order to block radiation noise caused by magnetic flux leakage from the magnetic core. A technique is disclosed that utilizes a pair of recesses provided on the outside or protrusions provided on the outside of the transformer case. Certainly, if the conventional techniques of Patent Documents 5 and 6 are used, the short ring can be positioned easily and reliably. However, the prior arts of Patent Documents 5 and 6 are all about the contents relating to the casing of the transformer, and the problem to be solved by the present invention (avoidance of reduction in heat dissipation efficiency due to winding of the short ring) is not found at all. It was not disclosed or mentioned.

  In view of the above problems, an object of the present invention is to provide a transformer capable of efficiently radiating heat while reducing noise leakage from a gap formed in a magnetic core.

  In order to achieve the above object, a transformer according to the present invention has a magnetic core in which a gap is formed, and as a means for shielding radiation noise from the gap, the magnetic core is covered so as to cover the gap. The transformer including the short ring is configured by winding the short ring a plurality of times so that the short ring also functions as a heat dissipation means. Thus, by winding the short ring a plurality of times, the heat capacity can be increased by increasing the volume of the short ring, so that the heat taken from the gap can be sufficiently buffered by the short ring. Therefore, it is possible to efficiently dissipate heat while reducing noise leakage from the gap portion formed in the magnetic core.

  In the transformer configured as described above, the short ring may be a foil tape formed of copper, silver, gold, or aluminum. In this way, if the short ring is formed of a metal having a large thermal conductivity and heat capacity, the heat generated in the gap can be quickly taken away and the heat can be buffered, so that the smooth heat Exchange becomes possible, and it becomes possible to avoid the excessive temperature rise of a transformer.

  In the transformer configured as described above, the adhesive for attaching the short ring may include copper, silver, gold, or aluminum. In this way, by attaching a short ring using an adhesive containing a metal having a large thermal conductivity and heat capacity, it is possible to suppress an increase in thermal resistance and a decrease in heat capacity between the bonded short rings. Smooth heat exchange is possible, and excessive temperature rise of the transformer can be avoided.

  In the transformer configured as described above, the short ring may be a foil tape having a smooth surface. By adopting such a configuration, it is possible to prevent an increase in thermal resistance by preventing a gap from being formed between the bonded short rings, thereby enabling smooth heat exchange and excessive temperature rise of the transformer. Can be avoided.

  As described above, the transformer according to the present invention can efficiently dissipate heat while reducing noise leakage from the gap formed in the magnetic core.

  As a result of intensive studies to reduce heat leakage while reducing noise leakage from the gap portion formed in the magnetic core, the present inventors have found that the short ring has extremely high thermal conductivity such as copper and aluminum. Because it is made of a very high material, it can quickly take away the heat generated in the gap, but its volume (mass) is extremely small and its heat capacity is very small. It was found that the short ring itself was heated without catching up heat radiation to the air, resulting in excessive temperature rise of the transformer, and the present invention was achieved.

  FIG. 1 is a perspective view showing an embodiment of a transformer according to the present invention. As shown in the figure, the transformer of this embodiment has a magnetic core 1 in which a gap portion 2 is formed, and as a means for shielding radiation noise from the gap portion 2, the magnetic core 1 and the bobbin so as to cover the gap portion 2. 4, the short ring 3 is wound around, and the short ring 3 is wound a plurality of times so that the short ring 3 also functions as a heat radiating means.

  In this way, by winding the short ring 3 a plurality of times, the volume (mass) of the short ring 3 can be increased to increase the heat capacity, so that the heat taken from the gap portion 2 can be sufficiently buffered by the short ring 3. It becomes possible. Accordingly, it is possible to efficiently dissipate heat while reducing noise leakage from the gap portion 2 formed in the magnetic core 1, and to improve the temperature rise of the transformer to a level that does not cause a problem in practical use. It becomes possible.

  For example, for a transformer with an EER42 size (W44-54 [mm] × D31-33 [mm] × H50-53 [mm]) and a side gap length of 0.6 [mm] on one side, a width of 15 [mm], When the short ring 3 having a thickness of 0.035 [mm] (thickness of the base material only) is wound and driven by an AC power source of 100 [kHz], the temperature of the coil wound around the bobbin 4 is measured. When the coil is wound only once (that is, in the case similar to the conventional case), the coil temperature has been increased to 100 [° C.] with respect to the ambient temperature 25 [° C.], whereas when the coil is wound three times, The rise in coil temperature could be suppressed to 80 [° C.]. Further, when the short ring 3 was wound five times, the temperature could be reduced to 60 [° C.].

  As described above, the transformer of this embodiment can effectively suppress an increase in coil temperature without increasing the size of the transformer, so that noise leakage can be achieved while meeting demands for miniaturization and lightening. Both reduction and improvement of heat dissipation efficiency can be realized.

  Further, in the transformer according to the present embodiment, since the thickness of the short ring 3 is increased, radiation noise from the gap portion 2 can be shielded at a level similar to or higher than the conventional level. Therefore, for example, if the switching power supply is configured using the transformer of the present embodiment, the filter circuit portion of the switching power supply can be simplified, so that the area occupied by the electronic components mounted on the board can be reduced, and the power supply can be reduced. It is possible to realize downsizing.

  In the transformer of this embodiment, a foil tape formed of copper, silver, gold, or aluminum is used as the short ring 3. Thus, by forming the short ring 3 with a metal having a large thermal conductivity and heat capacity, it is possible to quickly take away the heat generated in the gap portion 2 and buffer the heat. Smooth heat exchange is possible, and excessive temperature rise of the transformer can be avoided.

  In the transformer of this embodiment, the short ring 3 is attached using an adhesive containing any one of copper, silver, gold, or aluminum. In this way, by using an adhesive containing a metal having a large thermal conductivity and heat capacity, it is possible to suppress an increase in thermal resistance and a decrease in heat capacity between the bonded short rings, so that smooth heat exchange is possible. This makes it possible to avoid an excessive temperature rise of the transformer.

  In the transformer of this embodiment, a foil tape having a smooth surface is used as the short ring 3. By adopting such a configuration, it is possible to prevent an increase in thermal resistance by preventing a gap from being formed between the bonded short rings, thereby enabling smooth heat exchange and excessive temperature rise of the transformer. Can be avoided. However, the outermost surface portion of the short ring 3 may be embossed or the like to increase the heat exchange area with air.

  In the transformer of this embodiment, if the width and thickness of the short ring 3 are increased, the same effect as described above can be obtained even if the number of windings of the short ring 3 is reduced. However, if the width or thickness of the short ring 3 is excessively increased, the adhesion with the magnetic core 1 and the adhesion between the short rings cannot be maintained, and there is a possibility that the noise shielding performance and the heat radiation performance may be reduced. Careful attention should be paid.

  As shown in FIG. 1, the transformer of this embodiment is a so-called EE type transformer, and the magnetic core 1 is formed by opposing a pair of E type magnetic cores having a central magnetic leg and side magnetic legs, and a gap. The portion 2 is formed on the side magnetic leg. Thus, it can be said that the present invention is suitable not only for the center gap structure transformer but also for the side gap structure transformer. However, the scope of application of the present invention is not limited to this, and any transformer such as an EI type or UU type can be widely applied as long as the transformer has a magnetic core in which a gap portion is formed. Is possible.

  The present invention can be widely applied to transformers in general, but is particularly useful for a copying machine or printer switching power supply that requires a reduction in size and weight.

These are perspective views which show one Embodiment of the trans | transformer which concerns on this invention. These are perspective views which show one prior art example of a transformer.

Explanation of symbols

1 Magnetic core
2 Gap 3 Short ring 4 Bobbin

Claims (4)

In a transformer having a magnetic core in which a gap portion is formed and winding a short ring including the magnetic core so as to cover the gap portion as a means for shielding radiation noise from the gap portion,
A transformer, wherein the short ring is wound a plurality of times so that the short ring also functions as a heat dissipation means.   The transformer according to claim 1, wherein the short ring is a foil tape formed of copper, silver, gold, or aluminum.   The transformer according to claim 1, wherein the adhesive for attaching the short ring contains any one of copper, silver, gold, and aluminum.   The transformer according to claim 1, wherein the short ring is a foil tape having a smooth surface.

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