Abstract: Coil frames and transformers are provided. A coil frame includes a sub-coil-frame and an extended frame. The sub-coil-frame is utilized for winding a metal coil thereon. The extended frame is attached to the sub-coil-frame. The extended frame has a hole and a protrusion. The hole of the coil frame can be connected with the protrusion of another coil frame.

Abstract: A magnetic element includes a first wire, a second wire, a third wire, a fourth wire and a first single-strand wire. The first wire is disposed at a first side of the magnetic element, and has a first end and a second end. The second wire is disposed at the first side of the magnetic element, and has a third end and a fourth end. The third wire is disposed at a second side of the magnetic element, and has a fifth end and a sixth end. The fourth wire is disposed at the second side of the magnetic element, and has a seventh end an eighth end. The first single-strand wire has one terminal simultaneously connected to the second end and the fourth end.

Abstract: The present invention relates to a circuit carrier and transformer assembly. The circuit carrier and transformer assembly includes a circuit carrier and a transformer. The transformer includes a bobbin with multiple bobbin bases. The circuit carrier includes multiple receiving holes corresponding to respective bobbin bases of the bobbin. The bobbin bases are received in respective bobbin bases when the transformer is mounted on the circuit carrier.

Abstract: In a transformer including a coil part having a first bobbin to which a coil is mounted, a second bobbin to be fitted to the first bobbin combined to each other, the coil part being sandwiched between magnetic cores from above and below, the first bobbin includes at least one lead drawing through holes on a periphery on the inner peripheral side of a coil mounting surface, and at least one of coil-drawn-leads of the coil is drawn through the lead drawing through hole. With this transformer, coming out of the coil-drawn-lead, displacement, and erroneous wiring are prevented, and hence the inserting capability of the coil is improved. Therefore, the workability is remarkably improved, and hence a product which is low in price can be provided.

Abstract: A transformer-based power conversion system includes a primary coil is provided in a current path that includes a single energy switch. An oscillator is coupled to a control input of the energy switch. The design conserves switch-based losses as compared to prior designs because a single switch is provided in a current path occupied by the primary coil. The design also provides improved conversion efficiency because parasitic capacitances associated with the energy switch cooperate with charge transfers generated by the oscillator.

Abstract: An assembly involves an integrated circuit die that is bonded, e.g., flip-chip bonded, to a non-semiconductor substrate by a plurality of low-resistance microbumps. In one novel aspect, at least a part of a novel high-frequency transformer is disposed in the non-semiconductor substrate where the non-semiconductor substrate is the substrate of a ball grid array (BGA) integrated circuit package. At least one of the low-resistance microbumps connects the part of the transformer in the substrate to a circuit in the integrated circuit die. At two gigahertz, the novel transformer has a coupling coefficient k of at least at least 0.4 and also has a transformer quality factor Q of at least ten. The novel transformer structure sees use in coupling differential outputs of a mixer to a single-ended input of a driver amplifier in a transmit chain of an RF transceiver within a cellular telephone.

Abstract: A current transformer detects a sine-wave alternating current having a maximum effective current value Imax(Arms) and a frequency f(Hz) and a half-sine-wave rectified current having a maximum peak value Ipeak(Aop) and a frequency f(Hz) in a primary winding, consisting of at least one magnetic core with one turn of primary winding and at least one multiple turns of secondary winding to which a detecting resistor is connected.

Abstract: A low profile coil-wound bobbin is disclosed. A low profile coil-wound bobbin includes a spool and a terminal. The spool is configured to have a coil-wire arrangement wound around the spool. The terminals are to be coupled to the coil-wire arrangement and a first side of a circuit board. The terminal is configured to mechanically and/or electrically couple the low profile coil-wound bobbin to the first side of the circuit board such that the low profile bobbin extends through the circuit board to another side of the circuit board.

Abstract: A transformer apparatus and a transformer shielding method are provided for shielding external electronic noises and protecting against erosion. The transformer apparatus comprises a toroidal core, a primary winding, a secondary winding, a protection tape, a metal foil, and an UL tube. The primary winding and the secondary winding are wound around the toroidal core at opposite side to each other. The protection tape is wrapped around the primary winding and the secondary winding. The metal foil encloses the protection tape. The UL tube enfolds the metal foil. The transformer shielding method comprises wrapping a primary winding and a secondary winding of the transformer apparatus by a protection tape, enclosing the protection tape by a metal foil, and enfolding the metal foil by an UL tube.

Abstract: At least two or more flat rectangular wires having been fed separately or simultaneously (two or more are superimposed) are integrated by being pinched in a width direction and a thickness direction by at least two or more pairs of rollers and are rolled and formed simultaneously in a forming part to be formed into two or more flat rectangular electric wires. The two formed electric wires are stacked in layers in a wind-up part while being wound into a disk shape to provide a multi-stage coil. Two or more systems up to the forming part of the winding apparatus may be disposed in a planar layout. Each system may supply one flat rectangular electric wire separately, and the supplied electric wires may be stacked in layers in the wind-up part while being superimposed. The coil may be molded entirely.

Abstract: Toroidal inductive devices are manufactured with high efficiency through the use of bobbin winding techniques or wound magnetic pattern members.

Abstract: The present invention provides a high voltage, step-up, high current DC pulse type transformer with increased coupling coefficient between the primary and secondary windings through close proximity of the primary winding turns and secondary winding turns by means of transformer construction that provides a plurality of winding bays for a high voltage secondary winding physically located in close proximity to the primary winding. The plurality of winding bays for the secondary winding are provided by means of a frame and separate thin insulation layer where the thin insulation layer provides the barrel for all or part of the secondary winding.

Abstract: Embodiments of the invention may provide for power amplifier systems and methods. The systems and methods may include a power amplifier that generates a first differential output signal and a second differential output signal, a primary winding comprised of a plurality of primary segments, where a first end of each primary segment is connected to a first common input port and a second end of each primary segment is connected to a second common input port, where the first common input port is operative to receive the first differential output signal, and where the second common input port is operative to receive the second differential output signal, and a single secondary winding inductively coupled to the plurality of primary segments.

Abstract: Example embodiments of the invention may provide systems and methods for multiple transformers. The systems and methods may include a first transformer that may include a first primary winding and a first secondary winding, where the first primary winding may be inductively coupled to the first secondary winding, where the first transformer may be associated with a first rotational current flow direction in the first primary winding.

Abstract: There is provided a transformer improved in leakage inductance including: a core having first, second and third legs electromagnetically coupled to one another; a primary winding formed of a conductor having one end and another end receiving power from the outside and dividedly wound around the first, second and third legs; and a secondary winding wound around at least one of the first, second and third legs and receiving induced power by electromagnetic induction with the primary winding.

Abstract: A manufacturing method for the inductor/transformer is disclosed. A simulator is used to simulate the inductance, the quality factor, and the self-resonance frequency of said inductor/transformer to generate at least one group of the area size, the number of the conductive layer, the line width, the number of turns, and/or the line space of the conductive layers and the first conductive layer; the inductor/transformer is manufactured according to the factors. Thereafter, the Monte-Carlo simulation is used to initiate the process variability analysis of the factors of the conductive layer and the first conductive layer, and the geometric size of the inductor/transformer can be modulated according to the results of the process variability analysis during the manufacturing process, such that the inductor/transformer can be manufactured by the process of the generic logic circuit.

Abstract: The present invention includes a high voltage transformer and high voltage inductor having a high resistivity magnetic core and multiple secondary windings without needing insulation between the high resistivity core and multiple secondary windings.

Abstract: An inductor with self-damping properties for use in multiple applications including for high power broadband frequency applications is provided by a coil having an input end and an output end and wound about a core of magnetically permeable material and an eddy current generator incorporated either at the time of manufacture or post manufacturing. The core can be air (e.g., a hollow coil of wire). Alternative core materials are iron, iron powder, steel laminations and other appropriate materials. The core may be incorporated into some form of frame whether I shaped, U shaped, E shaped or of an encapsulated shape arrangement. The inductor's Q value may be changed selectively by deliberately inducing eddy currents in preferred locations. The eddy currents are induced into the inductors and have the effect of introducing a back EMF which is designed and scaled appropriately to adjust the Q value at the desired frequency resulting is less phase distortion.

Abstract: The coil component comprises a primary coil, and a first secondary coil and a second secondary coil which are opposed to the primary coil. A first terminal is a terminal of the first secondary coil, that is a terminal for connection to one end of a lamp, and a second terminal is a terminal of the second secondary coil, that is a terminal for connection to the other end of the lamp. The first secondary coil and the second secondary coil are coaxially disposed, and the first terminal and the second terminal are reverse in polarity.

Abstract: An electrical winding structure configured for use in assembling a plurality of electrical winding structures in an installed orientation wound about a central member includes: a unitary segmented strip. First portions of the unitary strip are oriented about a first axis. Second portions of the unitary strip are oriented about a second axis substantially perpendicular with the first axis. Each of the first portions and the second portions have a thickness, have a width greater than the thickness and have a length at least as great as the width. The first and second portions are oriented to effect arranging the electrical winding structure at predetermined loci during winding to clear the winding path to establish a predetermined plurality of strata in the installed orientation.

Abstract: There is provided an isolated power converter. More particularly, in one embodiment, there is provided a power converter including a first magnetic core having a primary winding and a secondary winding around the first magnetic core. The power converter also includes a second magnetic core having a first leg, a second leg coupled to the first leg, and a third leg coupled to the first and second legs, wherein a part of the third leg is equidistant from the first leg and the second leg. The power converter also has a first winding encircling the first leg, a first end of the first winding coupled to the secondary winding, a second winding encircling the second leg, a first end of the second winding coupled to the secondary winding, and a third winding encircling the third leg, a first end of the third winding coupled to a second end of the first wining and to a second end of the second winding.

Abstract: The configurations of a dielectric barrier discharge lamp (DBDL) system and the driving method thereof are provided in the present invention. The proposed DBDL system includes a driver circuit receiving a DC input voltage and generating an AC output voltage, including a transformer having a primary winding and a secondary winding, a dielectric barrier discharge lamp coupled to the secondary winding and a burst mode dimming circuit including a first switch. In which, the first switch is turned on when the first switch is starting such that the first switch and the primary winding forms a conducting path so as to apply a driving high voltage to the DBDEL and turn off the first switch after the DBDL is breaking through by the driving high voltage such that a driving normal voltage is applied to the DBDL.

Abstract: Combined type transformer includes: a transformer core; first and second coils provided with respect to the transformer core; first and second inductor cores provided around the first coil; and third and fourth inductor cores provided around the second coil. The transformer core and the first and second coils constitute a transformer, the first coil and the first and second inductor cores constitute a first inductor, and the second coil and the third and fourth inductor cores constitute a second inductor.

Abstract: A planar magnetic device comprising a planar core, a first plurality of planar windings having apertures, a second plurality of planar windings having apertures, a planar core surrounding at least a portion of the first and second plurality of planar windings, a first terminal having first and second legs separated by about ninety degrees, and a second terminal having first and second legs separated by about ninety degrees, wherein the first leg of the first terminal is positioned through the apertures in the first plurality of planar windings, the first leg of the second terminal is positioned through the apertures in the second plurality of planar windings such that the second leg of the first terminal is adjacent the second leg of the second terminal.

Abstract: A transformer for an inverter includes: a bobbin including at least one barrier rib between a pair of opposing side-walls, and a coil winding part divided into a low voltage side and a high voltage side by the barrier ribs, two or more strands of a coil being wound around the coil winding part of the low voltage side; and a ferrite core inserted into the bobbin, the ferrite core surrounding the bobbin and guiding a magnetic flux.

Abstract: Transformers are provided. A transformer comprises a ferromagnetic core unit; a bobbin coupled with the ferromagnetic core unit; at least a winding unit as a primary winding and at least a plate as a secondary winding. Also, some of the winding units can act as a secondary winding. At least a winding unit and at least a plate are alternatively stacked in a staggered manner. A conductive wire is wound around the winding unit.

Abstract: Interleaved three-dimensional (3D) on-chip differential inductors 110, 120 and transformer 100 are disclosed. The interleaved 3D on-chip differential inductors 110, 120 and transformer 100 make the best use of multiple metal layers in mainstream standard processes, such as CMOS, BiCMOS and SiGe technologies.

Abstract: An inverter transformer includes a core structure, bobbins each including a spool portion and first and second terminal blocks and having a part of the core structure inserted therein, and primary and secondary windings wound around the bobbin, wherein the first and second terminal blocks have recesses formed at their end faces and adapted to lodge terminal pins to tie wire ends of the secondary winding therearound, the distal tip ends of the terminal pins lodged in the recesses of the first and second terminal blocks are positioned either flush with or inward of the end face of the first and second terminal blocks, parts of the core structure are located above the recesses, and the end faces of the core structure oriented substantially orthogonal to an extending direction of the terminal pins are positioned either flush with or outward of the distal tip ends of the terminal pins.

Abstract: A high voltage split core transformer and method of assembling same is provided by which the coupling factor is improved. A split core assembly is surrounded by a secondary winding that is precisely located in a burner assembly housing. Conductive members are encased within the housing and, in conjunction with traces provided on a printed circuit board enclosing the housing cavity, define first and second primary windings about the core secondary winding. This arrangement reduces the number of turns in the secondary winding and allows the use of larger cross-sectional wire which increases the current carrying capability thereof, making the transformer suitable for D1-D5 automotive headlamp applications.

Abstract: Disclosed is a transformer having a multilayered winding structure. The transformer is supplied with alternating current power, and transfers the power to another circuit by electromagnetic induction. The transformer includes a core section having a hollow section, and primary and secondary windings isolated electrically from each other and wound around the core section. Each of the primary and secondary windings has a multilayered structure in which a plurality of metal plates are laminated with gaps therebetween and are coupled to each other at one side ends thereof, and the metal plates of the primary and secondary windings are inserted into and coupled to each other at the other side ends thereof in such a manner that the metal plates of the primary winding are alternately inserted into the gaps of the second windings.

Abstract: A transformer-type compact and thin coil device having a high coupling degree between a primary coil and a secondary coil, and a transformer device in which a plurality of sets of the transformer-type coil devices are incorporated. A coil device includes a first winding portion in which a primary and secondary coil wires are wound in bifilar form so as to arrange them alternately in a plane, a second winding portion in which a secondary coil wire is wound to arrange it in a plane parallel to the plane of the first winding portion, and a secondary coil connecting portion which connects an inner diameter portions of the secondary coil wires of the first and second winding portions. A transformer device is formed by incorporating a plurality of sets of the transformer-type coil devices each formed in above manner.

Abstract: A transformer includes a primary coil assembly and a secondary coil assembly juxtaposed in a stack and which are electromagnetically inductively coupled and substantially symmetrical to one another. The primary coil assembly includes a plurality of primary coils coplanar with first insulation layers, respectively, and symmetrical to each other, and a first via unit connecting adjacent ones of the primary coils to each other. The secondary coil assembly includes a plurality of secondary coils coplanar with a plurality of second insulation layers, respectively, and symmetrical to each other, and a second via unit connecting adjacent ones of the secondary coils to each other.

Abstract: The present invention discloses a transformer used in a charger circuit, in which the input side of the transformer is connected to an AC input and PWM control circuit of the charger circuit, the output side of the transformer is connected to a constant current and/or constant voltage control circuit of the charger circuit. The AC input, PWM control circuit, the constant current and/or constant voltage control circuit are coupled through an optical coupling element, wherein the transformer includes a main output winding and an auxiliary output winding, and the auxiliary output winding is used to supply power for the optical coupling element and the constant current and/or constant voltage control circuit. The present invention further provides a high performance charger circuit adopting the transformer described above for improving electromagnetic compatibility, conversion efficiency and short circuit characteristic.

Abstract: An electromagnetic device and a high-voltage generating device which are thin and improved in the characteristics are provided in which a magnetic core is made of a cylindrical form of a ferrite material having a higher intrinsic resistance. A winding is provided by winding a flat rectangular wire conductor in an edge-wise winding form directly on substantially the entire length of the magnetic core. As any insulator such as a coil bobbin is not needed between the flat rectangular wire conductor and the magnetic core, the winding can be decreased in the overall size or thickness thus contributing to the dimensional reduction of the electromagnetic device. Also, as its flat rectangular wire conductor is wound directly on the magnetic core, the winding can be minimized in the length and thus the overall resistance. Moreover, as there is no gap between the winding and the magnetic core, the self-inductance can be reduced while the size and the number of turns of the winding remain unchanged.

Abstract: A power converter employing a magnetic device including a magnetic core and first and second tapped windings. Each winding of the magnetic device has first and second winding sections, respectively, coupled to the magnetic core, wherein the first and second winding sections are formed from a formed and folded planar conductive sheet. The magnetic core includes a common leg, a plurality of outer legs, and a top plate. The first and second winding sections are constructed with a formed and folded planar conductive sheet formed with structures usable as pins in a through-hole, surface-mount, or combined printed wiring board assembly process. The outer legs at either end of the magnetic core are positioned back from magnetic core ends, and the magnetic core is formed with a stepped structure to accommodate winding pins in a surface-mount printed wiring board assembly process.

Abstract: Apparatus for reducing electrical earth displacement current flow generated by wound components is disclosed. In one aspect, an apparatus includes a plurality of layers of an input winding wound around an energy transfer element core. An outer layer of the plurality of layers of the input winding is wound with a number of turns different than the number of turns in substantially each of the inner layers of the plurality of layers of the input winding. An output winding is wound around the energy transfer element core with substantially the same number of turns as the number of turns of the outer layer of the plurality of layers of the input winding to reduce substantially a capacitive displacement current flowing between the input and output windings.

Abstract: The present invention provides a transformer comprising a core set constructed by a first core and a second core. The first core and second core define a space, a circuit board with at least one hole is disposed in the space; wherein the winding assembly comprises an insulation coil with an extending portion correspondingly passing through the holes and a plurality of conductive pieces are disposed in the insulation coil.

Abstract: The present invention provides an in-line filament transformer for a vacuum device. The filament transformer comprises: a core; a primary winding and a secondary winding wound around the core, wherein the secondary winding is biased at a high voltage and the primary winding is placed in line with the secondary winding; and a shield for shielding the primary winding. In an embodiment, the transformer comprises a bobbin for incorporating primary winding and secondary winding. An arrangement of increasing creepage distance is incorporated in the bobbin by providing plurality of sections on the bobbin. The invention also provides a shield in the primary section of the bobbin for shielding the primary winding from the secondary winding. In an embodiment the shield is in the form of shield winding of thin wires wound in a defined manner.

Abstract: A magnetic element capable of obtaining a desired characteristic and at the same time having high productivity that enables cost reduction is provided. The magnetic element includes a first coil (50) to which a signal is inputted, a second coil (60) to which the signal inputted to the first coil (50) is transmitted, and includes a first core (20) having a first columnar leg portion (26) on which the first coil (50) is wound and a first peripheral wall portion (22, 23, 24) arranged on the periphery of the first columnar leg portion (26), and a second core (30) having a second columnar leg portion (36) on which the second coil (60) is wound and a second peripheral wall portion (32, 33 34) arranged on the periphery of the second columnar leg portion (36).

Abstract: The invention provides an on-chip transformer balun formed among N successive isolating layers. The transformer includes a primary winding and a secondary winding. The primary winding includes a plurality of first semi-turn coils, a plurality of second semi-turn coils, a plurality of metal junctions, and a plurality of first metal bridges. The secondary winding includes a plurality of third semi-turn coils, a plurality of fourth semi-turn coils, and a plurality of second metal bridges. The first semi-turn coils are connected with the second semi-turn coils by the metal junctions and the first metal bridges. The third semi-turn coils are connected with the fourth semi-turn coils by the second metal bridges. By use of the multi-layer first metal bridges, the transformer according to the invention allows a larger input current than a conventional on-chip transformer.

Abstract: An inductor with self-damping properties for use in multiple applications including for high power broadband frequency applications is provided by a coil having an input end and an output end and wound about a core of magnetically permeable material and an eddy current generator incorporated either at the time of manufacture or post manufacturing. The core can be air (e.g., a hollow coil of wire). Alternative core materials are iron, iron powder, steel laminations and other appropriate materials. The core may be incorporated into some form of frame whether I shaped, U shaped, E shaped or of an encapsulated shape arrangement. The inductor's Q value may be changed selectively by deliberately inducing eddy currents in preferred locations. The eddy currents are induced into the inductors and have the effect of introducing a back EMF which is designed and scaled appropriately to adjust the Q value at the desired frequency resulting is less phase distortion.

Abstract: An electrical reactor assembly and method of assembly is disclosed. The reactor is formed from a combination of a magnetic T-core and a pair of magnetic L-cores. A plurality of comb-like separators is placed over a vertical portion of the T-core. A wire, with a rectangular cross-section, is wound about the vertical portion of the T-core thereby forming a coil. The comb-like separators electrically isolate the wire from adjacent windings and the T-core. The L-cores are attached to the T-core such that they flank two sides of the coil. A plurality of taps is formed on a side of the coil that is not flanked by one of the L-cores. The taps are formed by extending individual windings further from the T-core than other common windings. Preferably, a hole is formed through the rectangular wire at the taps to provide a secure electrical connection to the wire.

Abstract: An energy transfer element having windings. In one aspect, the energy transfer element includes a first winding wound around a core, the first winding has a first end and a second end. A second winding is wound around the core. The second winding has a first end and a second end. The first winding is capacitively coupled to the second winding to provide a transfer of energy from the first winding to the second winding. A third winding is wound around the core. The third winding has a first end and a second end. The first end of the third winding is electrically coupled to the first end of the second winding. The second end of the third winding is uncoupled such that an influence of an electrostatic field to be produced by the first and second windings relative to the core are to be cancelled by an electrostatic field to be created by the third winding.

Abstract: In an inductor having a core and first and second coils wound upon the core, the wire of the first coil and the wire of the second coil lie are wound so as to lie parallel to each other and contact the core. The winding starting position of the first coil is made to coincide with the winding starting position of the second coil along the axial direction of the core and is offset from the winding starting position of the second coil along the winding direction of the core. As a result, the area factor of the coils in the winding area of the inductor can be improved and the size of the inductor reduced.

Abstract: A method of winding a coil of a transformer in an inverter of a liquid crystal display including a bobbin wound with a coil and a core introduced into the bobbin, the method includes forming a coil winding part having no protrusion member at the bobbin so as to exclude an interference caused by the protrusion member from a path wound with the coil; and continuously winding the coil from one side of the coil winding part to another side thereof.

Abstract: A transformer having a leakage inductance control structure includes a primary coil, a secondary coil formed at a selected coil ratio relative to the primary coil to transform voltage and output electric power, and a leakage inductance control coil which is wound on the secondary coil in an insulation manner according to a selected coupling efficiency and electrically connected to the primary coil. Through electromagnetic coupling of the leakage inductance control coil and the secondary coil a power control signal is output and sent to the primary coil to control leakage inductance of the primary coil.

Abstract: The coil component of the present invention is configured in that one secondary winding is coiled between central portion and end portion of outer magnetic leg, and the other secondary winding is coiled between central portion of outer magnetic leg and first gap portion. Secondary windings and are coil in directions opposite to each other, and secondary winding is less in the number of windings than secondary winding.

Abstract: A preferred embodiment of a three-phase transformer includes a first, a second, and a third winding leg, and a first, a second, and a third winding positioned around the respective first, second, and third winding legs. The first, second, and third windings each includes an electrical conductor wound into a plurality of overlapping layers each formed by a plurality of adjacent turns of the electrical conductor, and an insulating material without end fill positioned between each of the overlapping layers. The electrical conductor has a transition portion formed therein between a first and a second of the overlapping layers. The transition portion is at least one of bent to form an offset in the electrical conductor, and secured to at least one of the plurality of adjacent turns.

Abstract: A method for assembling electrical windings about an axis, the windings being strips and wound in alternating strata with their widths parallel with the axis, includes the steps: (a) Winding a first-wound winding in a winding path about the axis establishing a first stratum. (b) Arranging the first-wound winding to clear the winding path. (c) Winding one or more next windings to establish next-wound windings in the winding path until at least one next stratum is established. (d) Interleaving earlier-wound windings to establish the plurality of strata; the interleaving including the steps of: (1) rearranging a next-to-be-wound winding to realign with the winding path; (2) winding the next-to-be-wound winding in the winding path until a next stratum is established; (3) arranging the next-to-be-wound winding to clear the winding path; and (4) repeating steps (d)(1) through (d)(3) until the assembling is complete.

Abstract: A magnetic element including coils; a first core and a second core each of which has a planar plate portion, outer leg portions and a middle leg portion which is inserted into aforesaid coil; and an intermediate core to form a closed magnetic circuit which is disposed between the aforesaid first core and the aforesaid second core in a manner connecting integrally with the aforesaid first core and aforesaid second core. In addition, the magnetic element is made into a configuration that has relations of S1?S3 and also S1?S2 when a cross-sectional area of the middle leg portion of the aforesaid first core is S1, a cross-sectional area of the aforesaid intermediate core is S2 and a cross-sectional area of the middle leg portion of the aforesaid second core is S3.