Inductor devices – With closed core interrupted by an air gap
Reexamination Certificate
2002-05-31
2003-11-18
Lee, Wilson (Department: 2821)
Inductor devices
With closed core interrupted by an air gap
C336S066000, C336S192000
Reexamination Certificate
active
06650218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure of an inverter transformer employed in DC/AC inverter circuits for lightning an electrical discharge lamp. More specifically, the present invention relates to a structure of an inverter transformer which can be easily manufactured and in which leaking of magnetic flux from the joining portion of a pair of cores to the outside is prevented.
2. Description of the Related Art
A transformer in which a primary winding and a secondary winding are gripped on both sides by a pair of cores composed of a magnetic material and a prescribed electromagnetic coupling is conducted has been known in prior art as a transformer used in DC/AC inverter circuits for lightning an electrical discharge lamp employed as a back light for liquid crystal displays and the like. Such inverter transformers are disposed in narrow spaces and thin structures thereof are needed. In one example of the conventional transformers of this type, a structure is employed in which a primary winding is connected to an output terminal of an oscillation circuit (inverter) generating a high frequency and a secondary winding is connected to a discharge lamp via a ballast capacitor or the like, and in another example, a structure is employed in which part of the ballast capacitor is replaced with a choke coil.
A structure shown by a cross-sectional view in
FIG. 1
is an example of an inverter transformer that has been typically used in prior art, this inverter transformer comprising a primary winding, a secondary winding, and a pair of cores arranged facing each other and forming a closed magnetic circuit, wherein electromagnetic coupling is formed by the primary winding, secondary winding, and cores. In
FIG. 1
, the reference numeral
101
stands for an E-type core, and
701
,
601
—the primary winding and secondary winding wound on side legs
103
of the E-type core.
The reference numeral
201
stands for an I-type core arranged facing the E-type core
101
. A gap
202
is formed between a central legs
102
of E-type core
101
and the I-type core
201
, and between the side legs
103
of E-type core and the I-type core
201
. A spacer
203
composed of an electrically insulating material is usually sandwiched in the gap between the side legs
103
of E-type core and the I-type core
201
, and the E-type core
101
and I-type core
201
form a closed magnetic circuit through the spacer
203
. In the transformer of such a structure, magnetic resistance of the closed magnetic circuit can be changed and the degree of coupling of the primary winding
701
and secondary winding
601
can be adjusted by varying the thickness of spacer
203
. However, in order to adjust the degree of coupling, spacers of different thickness have to be prepared and individually used according to the desired degree of coupling. As a result, not only the number of parts is increased, but also the assembly operation becomes complex. Another drawback is that because of the spacer thickness, the height dimension of the transformer cannot be reduced and a thin transformer is difficult to fabricate. Further, in case of the above-described structure, there is also a risk of the magnetic flux leaking from part of spacer
203
to the outside and magnetically affecting electronic components in the vicinity of the transformer or peripheral equipment.
Japanese Patent Application Laid-open No. H10-335157 disclosed an inverter transformer in which the adjustment of coupling coefficient of primary and secondary windings was facilitated, this inverter transformer comprising a pair of cores forming a closed magnetic circuit, a primary winding, and a secondary winding, wherein the lower core of the pair of cores is composed of a rectangular flat plate-like portion and two cylindrical projections integrally formed on both ends thereof, a bobbin winding shaft is attached to each of the projections, the primary winding and secondary winding are wound on the two winding shafts, and part of the primary winding is wound on the secondary winding.
Japanese Patent Application Laid-open No. 2000-124045 disclosed a structure of an inverter transformer for multiple discharge lamps, wherein a plurality of outputs are obtained with a single inverter transformer in which the first and second secondary windings with the same number of turns are arranged in positions centrally symmetric about the primary winding, and the primary winding and the first secondary winding, and the primary winding and the second secondary winding are electromagnetically coupled with almost the same degree of coupling.
All of those inventions relate to structures in which the primary winding and secondary winding are arranged in parallel. In the structure of the invention disclosed in Japanese Patent Application Laid-open No. H10-335157, part of the primary winding is wound on the secondary winding. Therefore, the lead-out wire of the primary winding, that is, the winding on the low voltage side is arranged so that it intersects with the secondary winding, that is, the winding on the high voltage side. As a result, there is a risk of degrading the transformer performance, unless the electric insulating properties in each winding are improved. Another drawback of those inventions is that there is a risk of the magnetic flux leaking to the outside from the joining portion of the cores.
On the other hand, in Japanese Patent Application Laid-open No. 2000-124045, the primary winding is arranged in the center and secondary windings are arranged on both sides thereof. The drawback of such a structure is that in the pairs of the primary winding and the first secondary winding, and the primary winding and the second secondary winding, the coupling coefficients between the primary winding and secondary windings are difficult to adjust.
Japanese Patent Application Laid-open No. 2000-68132 disclosed a structure of an inverter transformer with a shape suitable for installation in a space with large outside dimensions and a narrow width, wherein the lateral cross section of a winding shaft of a bobbin has an elliptical contour, the side with a narrow width faces the side surface to which the terminals of the base part of the bobbin are attached, the winding shaft is molded integrally with the base part, a central leg with an elliptical cross section is formed in the central part of one core, outer legs are formed at the four corners of the core, the central leg is inserted into the hole of the winding shaft, and the outer legs abut upon the other core. In the invention disclosed in Japanese Patent Application Laid-open No. 2000-68132, since the side surface portion of the core is in an open state, there is a risk of the magnetic flux leaking and the adverse magnetic effects being produced on peripheral electronic components or electronic devices.
Japanese Patent Application Laid-open No. 2000-243633 discloses a bobbin for decreasing the thickness of a transformer with a conventional structure in which a primary winding and a secondary winding are arranged above and below. Thus, this patent application discloses a bobbin for an inverter transformer, comprising a cylindrical winding shaft molded integrally with the upper surface of a base part, wherein a cylindrical second winding shaft concentric with the above-mentioned winding shaft is provided in a position is outside the above-mentioned winding shaft, and a hook projecting to the outside is formed at the upper end of the second winding shaft.
The invention disclosed in Japanese Patent Application Laid-open No. 2000-243633 relates to a structure in which a secondary winding is arranged at the central shaft and a primary winding is arranged concentrically on the outside. However, as shown in
FIG. 3
of the specification relating to this application, in this invention, the primary winding is arranged so that it is exposed to the outside. As a result, there is a risk of the magnetic flux leaking to the outside and the adverse magnetic effects being produced on periphe
Kanesaka & Takeuchi
Lee Wilson
Sumida Corporation
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