Abstract: A flyback transformer for use with a horizontal sweep circuit and a CRT. The transformer includes a first "U-shaped" magnetic core member having first and second legs and a second "U-shaped" magnetic core member having first and second legs. The first legs of the first and second core members are spaced apart to form a gap therebetween, and the second legs of the first and second core members have planar faces that are in parallel abutting relationship with each other when the transformer is in an assembled relationship. Coil windings surround the gap and a portion of each of the first legs when the transformer is assembled.

Abstract: An apparatus is disclosed for a combined transformer and inductor for transmitting power between a source and a load. The apparatus comprises a transformer core and an inductor core which are magnetically independent from one another. A primary winding is wound about the transformer core and is electrically connected to the source by a primary connector. A secondary winding is wound about the transformer core and is electrically connected to the load by a secondary connector. An inductor coil is wound about the inductor core and is interposed in series with one of the primary and the secondary windings. A plurality of air gaps are interposed in the inductor core for providing an inductance in one of the primary and secondary windings. The air gaps are uniformly distributed about the inductor core for uniformly distributing heat generated at the air gaps about the inductor core.

Abstract: A small and thin step-up transformer suitable for use in an inverter or the like includes: a bobbin formed of an insulating material having a cylindrical winding shaft; a primary winding wound on said winding shaft; and a secondary winding wound in alignment in multi-layers from the inner side to the outer side thereof; and wherein the primary winding and the secondary winding are separated from each other at a portion of the bobbin to be arranged side by side in the central axial direction of the winding shaft and are electromagnetically coupled to each other.

Abstract: The present invention is comprised of an outside magnetic substance forming an endless loop, an inside magnetic substance formed inside of said outside magnetic substance and coil wound on the periphery of said inside magnetic substance. In a coil device of the present invention with gaps between both ends of said outside magnetic substance and said inside magnetic substance, notches or holes are provided in said outside magnetic substance for the purpose of inserting insert a jig therein so as to adjustably move the position of said inside magnetic substance, wherein said notches or holes correspond to the gaps provided in both ends of said inside magnetic substance. In said coil device, the inside magnetic substance can be adjusted and moved its position by pressing a bar-like jig through the notches or the holes provided in the outside magnetic substance. Thus, it has become possible to adjust the value of the inductance by about 25% experimentally.

Abstract: An electric noise absorber comprising at least two ferrite pieces having abutting planes, at least two case members containing the ferrite pieces respectively and being closed by means of engagement members, and a spring member provided in at least one of the case members for pressing the ferrite pieces against each other when the case members are closed. Since the case members for keeping the ferrite pieces in appropriate positions and the spring member for pushing up the ferrite pieces for close contact are separately molded, the case members are bestowed with strength and the spring member with elasticity, both suitable for their own purposes. The case members requires no apertures for biasing members and therefore outside magnetic substance is prevented from contacting with the ferrite pieces contained in the case members.

Abstract: A magnetic circuit with several magnetic components integrated on one or more common magnet cores is utilized in a current supply circuit known per se. The circuit comprises a transformer, the secondary winding ends of which are connected to uniform electrodes of a pair of rectifier diodes, the second electrodes of which are connected to one output terminal of the power supply circuit. Additionally, it includes two reactive components, and the first electrodes of the diodes are connected to the second output terminal of the power supply circuit via one of the reactive components. The number of turns of the two reactive components is essentially chosen to equal the number of secondary turns on the transformer. The two reactive components are positioned on each separate core part so that the resulting magnetic flux in common core parts substantially equals the difference between the magnetic flux of the two core parts, and the secondary winding of the transformer is positioned on the common core parts.

Abstract: A transformer and associated rectifier for supplying low voltage (e.g. 5 volts), high current (e.g. 1,500 amperes) power to a load such as a supercomputer, with a high electrical conversion efficiency and a high volumetric efficiency. The primary winding comprises a number of disc-shaped coils which are spaced apart from each other by coaxial single turn secondary coil elements which are interleaved between the primary coils. A core having E-shaped parts has an inner portion extending through the primary and secondary coils and an outer portion forming two windows with the inner portion, so that the coils extend through the windows. A rectifier assembly is mounted directly to plates which support and act as terminals to the secondary coils.

Abstract: The present invention provides a coil device including magnetic cores having gap regions and a coil wound to contain the gap regions. The present invention provides an improvement in which a shape of at least one of the opposing magnetic cores forming the gap regions is formed into a curve of logarithmic function from its base end to its extreme end, its most extreme end is provided with a gap adjusting flat surface and then a plurality of gaps are formed in the gap regions.With such an arrangement as above, the present invention provides the coil device capable of reducing a leakage magnetic flux produced around the gaps, preventing an abnormal generation of heat of the coils and further preventing a bad influence of noise against a peripheral apparatus.

Abstract: A contactless inductive power distribution system operating at 10 KHz has a self tuning resonant power supply connected to a resonant primary conductive path comprising a pair of parallel litz wire conductors each encapsulated within an insulated sheath and supported on a structural monorail beam on which a plurality of electric vehicles can run. Each vehicle has an electric motor capable of deriving power from a resonant pick-up coil wound on a ferrite core mounted on the vehicle in close proximity to the primary conductors. Each vehicle also has switching means capable of preventing a lightly loaded vehicle from presenting a reduced load to the resonant primary. In one version this comprises an isolating coil having a switch to switch the coil between an open circuit and a short circuit, so that when the switch is switched from one state to another state the power coupled between the primary conductive path and the pick-up coil is changed.

Abstract: An ignition coil device for an internal combustion engine includes an air gap between the two heat generating sources, the coil assembly and the power transistor unit, such that the coil assembly and the power transistor unit are thermally isolated from each other. Further, the primary winding bobbin has an inner projection inserted into the air gap of the core to maintain the gap. Furthermore, the primary winding bobbin and the secondary winding bobbin each has a first and a second bobbin attachment portion. First the high voltage tower attachment portion of the high voltage tower is engaged with the bobbin attachment portion on the secondary winding bobbin and the connector attachment portion of the connector is engaged with the bobbin attachment portion on the primary winding bobbin, to form respective integral sub-units.

Abstract: An electronic proximity switch dependent upon a magnetic field includes an HF resonant circuit adapted to be influenced by an approaching magnetic trigger. A coil arrangement includes a member drivable into magnetic saturation, with the member including an amorphous or predominantly amorphous metallic band of high permeability. A coil bobbin for accommodating the resonant circuit coil and the drivable member is made of a synthetic resin enriched with a pulverulent permeable material.

Abstract: A wire-wound bobbin serves as the core of a current transformer. A magnetic material flux path is disposed on the core that encircles the core coincident with the coils of the bobbin at least once and radially encircles the cross section of the core at lest once. The magnetic flux path comprises an assembly of distinct magnetic members positioned on the core and held in place by tape or the like.

Abstract: A coil device includes two magnetic cores each having a U-shape in section forming a closed magnetic path therein with their legs being opposed to each other and having a gap in such path, and a coil wound so as to cover the gap. In this structure, the mutually opposed portions of the magnetic cores in the region to form the gap are so shaped that the cross-sectional area of the fore end becomes smaller than that of the base end, thereby preventing concentration of any leakage magnetic flux on the gap portions while averting abnormal generation of heat in the coil to consequently eliminate harmful influence of noise on peripheral apparatus or components.

Abstract: An electromagnetic induction device which comprises a split-type core assembly comprising at least one winding formed thereon and first and second core segments each having at least two joint faces spaced apart from each other, the first and second core segments are connected together with the joint faces of one of the first and second core segments held in contact with the joint faces of the other of the first and second core segments, and a finely divided ferromagnetic material is interposed between the joint faces of the respective first and second core segments. The ferromagnetic material used has an average particle size sufficient to form a magnetic fluid medium.

Abstract: The current transformer of an electronic house-service meter has a ferromagnetic core which, except for an air gap, is closed. A measuring coil is inserted in the air gap and is fastened, and dimensioned so that it lies within the cross sectional area of the core.

Abstract: The novel magnetic core structure of this invention provides a combination of large differential type inductance and some common mode type inductance while accommodating common mode dc current in two parallel planar conductors such as bus bars or printed circuit lands. This combination of desirable functions is accomplished by incorporating both gapped and ungapped magnetic flux paths into a single core structure. The core structure is composed of two outer posts, two inner posts, and four link segments. The two inner posts of the present core are located in the position of the center leg of a tradiational E--E core structure. Unlike a conventional E--E core, the structural arrangement of the two inner posts provides both a gapped and an ungapped magnetic flux path. The ungapped magnetic flux path travels in a figure eight pattern, encircling each of the windows of the E--E core in one of the loops of the figure eight.

Abstract: A multiple phase inductor includes a magnetic core having two end pieces and a plurality of legs extending between the end pieces to form flux paths which pass through the end pieces and the legs. Each leg includes a stack of "I" shaped laminations which are positioned between the end pieces to form two gaps in at least one of the flux paths. A coil is wound around each of the legs and all of the coils present substantially the same inductance to an external power circuit. By providing two gaps in each of the legs, localized heating of the turns of the coils is reduced.

Abstract: The invention is directed to an ignition coil for use in an internal combustion engine. The ignition coil includes a center core which has a plurality of core members aligned. At least one permanent magnet is disposed between the core members. A primary winding and a secondary winding are mounting on the center core and permanent magnet. The permanent magnet is enclosed in the primary winding at least. An outer core having at least one core member is disposed around the primary winding and secondary winding. One end of the outer core is connected to one end of the center core, wheras the other end of the outer core is connected to the other end of the center core.

Abstract: The invention is directed to an ignition coil for use in an internal combustion engine. The ignition coil includes a core having at least two parts between which a gap is formed. A primary winding and a secondary winding are mounted on the core in such a manner that the gap of the core is substantially enclosed in the primary winding at least. A permanent magnet, whose cross section is larger in area than the cross section of the core, is disposed in the gap of the core to form a substantially closed magnetic circuit with the core. Preferably, there are disposed a primary bobbin for mounting thereon the primary winding and receiving therein the permanent magnet, and a secondary bobbin for mounting thereon the secondary winding and receiving therein the primary bobbin with the primary winding mounted thereon.

Abstract: A flyback transformer comprising a magnetic core assembled by joining together a pair of first and second U-shaped core halves each having two leg portions with end surfaces respectively joined in mutually abutting confrontation with respective gap spacers interposed therebetween at first and second core joint parts and a coil wound around the core joint parts. The coil includes, as an input winding, a primary winding divided into first and second primary windings which are wound at least around the two core joint parts of the core and are connected in parallel. By this arrangement, the magnetic fluxes generated at the two core joint parts cancel each other, and reduce the leakage flux field. Optionally, the two divided windings of the primary winding are each divided further into two windings wound around the leg portions on opposite sides of the spacers. At the same time, the first primary winding on the leg portion on one side and the second primary winding on the other side are connected in series.

Abstract: An improved inductive device has a U-shaped ferrite magnetic core with a base and a pair of parallel legs integrally extending from the opposite ends of the base. A straight ferrite magnetic core is disposed between the opposed core legs to define airgaps respectively between the ends of said straight core and the legs. A winding is disposed to surround the straight core. Each of the core legs is formed to have a generally flush surface over substantially the entire length thereof such that the portion of the flush surface is cooperative with the end of the straight core to define the airgap.

Abstract: A high frequency power transformer having a multi-element magnetic shield conforming to the surface of the structure including provisions for specific features of the magnetic circuit and winding assembly. The winding is disposed on one side of a four-sided magnetic circuit and is partially surrounded by a close fitting electrically continuous loop. The winding assembly includes an area having a higher electrostatic field and is surrounded by a second electrically continuous loop which is spaced apart from the winding assembly, providing significant electrostatic shielding and air movement over the winding assembly while avoiding arcing between the shield and the winding assembly due to the high electrostatic field.

Abstract: A shell-form transformer for charging an energy storage device contained in a battery powered impact device. The primary and secondary windings of the transformer are wound in a predetermined manner around the center leg of a core which has an air gap therein. The gap increases the reluctance of the center leg which decreases the flow of magnetic flux through the core which, in turn, enables the current applied to the transformer primary to be increased without causing the core to be saturated. As a result, the current applied to the transformer primary can be increased, thereby increasing the output voltage supplied from the transformer secondary which, in turn, enables rapid charging of the energy storage device.

Abstract: A switching mode power transformer for operation as feedback converter has a core which is made in only one piece and which does not require any particular finishing operations. The core has a center core part with windings thereon and outer core parts which are chamfered on their mutually remote sides to form outer surfaces which converge towards each other.

Abstract: A magnetic leakage transformer includes a paired cores each having five straight legs extending in the same direction from a common back beam, and associated with each other so that the leg's ends are opposed to each other with magnetic gaps between the paired central legs and between the two paired magnetic leakage flux legs neighboring at the both sides of the central legs. The opposed two paired five legs produces a paired inner passages into which a first winding unit is inserted and a paired outer passages into which a second one is inserted.

Abstract: The present invention concerns a transformer of the ferrite closed magnetic circuit type, with a gap.The gap is filled with a mastic such as the polysulphide or polyurethane mastics having a Shore hardness with constant behaviour as a function of temperature.

Abstract: An ignition coil for developing spark plug firing voltages. The magnetic current for the coil comprises an axially extending core that joins axially spaced annular parts. The core and parts can be formed of iron particles in a binder of electrical insulating material. A primary winding is disposed about the core and a secondary winding is disposed about the primary winding. An axially extending circular part that is formed of magnetic material is positioned to provide air gaps with outer surfaces of said annular parts. The circular part forms a shield that increases the capacitance of the secondary winding. The total stored magnetic energy does not vary substantially with variations in air gap length. The cross-sectional area A of the air gap is large as compared to the length L of the air gap so that the ratio A/L does not vary much with variations in L.

Abstract: In an ignition coil in which an air gap portion is provided at a portion of an iron core forming a closed magnetic circuit, which includes an exciting part iron core having a primary coil and a secondary coil wound therearound, and a strong permanent magnet is inserted in the air gap portion, the closed magnetic circuit is constructed to have the iron core and permanent magnet provided with respective suitable shapes, dimensions, properties, etc. so as to make most of the characteristics of the strong permanent magnet, thereby drastically reducing the size and weight of the ignition coil. Further, a concrete improvement of the construction of the closed magnetic circuit of the ignition coil is attained to assure excellent magnetoelectric conversion performance of the ignition coil.

Abstract: A push-pull transformer of a push-pull current-fed DC-DC converter is arranged so that the inductance of the primary side of the transformer diminishes equivalently, thereby reducing a conversion loss attributable to a distributed capacitance of the transformer. To equivalently reduce the inductance of the primary side, for instance, a gap is formed in the core of the transformer and/or an inductor is connected in parallel to any one of the windings of the transformer.

Abstract: There is disclosed an ignition coil for an engine which is arranged to connect a terminal end of a coil strand to a terminal member by pulling the terminal end of the coil strand out of a coil bobbin, positioning said terminal end of the coil strand in a U-shaped groove of a terminal member attached to the coil bobbin and then connecting the terminal end of the coil strand to said terminal member by fusing connection, while crushing the U-shaped groove of the terminal member, in which a guide member is provided on the coil bobbin to position the pulled out end of the coil strand at a predetermined position in the U-shaped groove of the terminal member.

Abstract: The invention provides an electromagnetic device such as a transformer which comprises one or more electrically conductive windings in a cylindrical magnetic frame. The magnetic frame defines a magnetic flux path having a length which is less than the length of the portion of the windings enclosed by the magnetic frame, and the device includes heat dissipation elements disposed about the windings and extending transversely from the windings. The magnetic frame comprises a number of toroidal core sections which are stacked end to end, so that the magnetic frame has an elongate tubular form. The heat dissipation elements are plates located between adjacent core sections.

Abstract: A pulse transformer for a flyback converter type switching power source has a ferrite core (10,11) with a pair of side legs (10a, 11a) and a center leg (10b, 11b) which is shorter than said side leg so that an air gap G is provided in the magnetic path along the center leg, and the windings on a bobbin (15) on said ferrite core is improved by positioning said gap G at the end portion of the center leg close to the end of the bobbin, and a dielectric belt (16b) on the bobbin (15) so that no winding exists around said gap. Thus, leakage flux around said gap does not interlink with the windings, and no eddy current flows in the windings, and a partial temperature raise in the windings is prevented.

Abstract: A high-frequency transformer for a microwave oven comprises: an E-shaped first core of ferrite of a low-voltage side; a primary winding wound around the first core over a coil bobbin; an E-shaped second core of ferrite of a high-voltage side disposed in opposition with the first core with a specific gap therebetween; a gap-filling insulation material interposed between the first and second cores; a secondary winding wound around the second core; and a grounding plate connected electroconductively between the first core and a bottom plate of the microwave oven, wherein the distance between the primary winding and the first core is greater than the gap between the two cores.

Abstract: The invention is directed to a transformer having notch gaps extending partially across the flux path of the transformer core and having a total gap volume which stores sufficient magnetic energy to substantially eliminate inductive voltage spikes in a clipped sinusoidal waveform applied to the primary of the transformer. As used in a low voltage lighting system in which the intensity of a filament lamp is regulated by a dimmer control which selectively clips the voltage applied to the transformer primary winding by an ac source, the invention substantially eliminates filament ringing.

Abstract: In a high-voltage transformer such as an ignition coil for internal combustion engines, a resin-crack preventing member is provided between an iron core and a resin which is impregnated into a coil case for electrically insulating a primary coil and a secondary coil in the coil case from the iron core as well as for firmly securing these coils and the iron core to the coil case. The resin-crack preventing member is moulded from a resinous material which is highly adhesive to the impregnated resin and which has a coefficient of thermal expansion similar to that of the impregnated resin. The resin-crack preventing member serves to prevent direct contact of the impregnated resin with the corners, side surfaces and inner surface of the iron core which has a coefficient of thermal expansion substantially different from that of the impregnated resin, thereby avoiding peeling off and cracking in the impregnated resin which would otherwise be caused by severe temperature changes.

Abstract: The invention provides a toroidal transformer with integrated self inductance device, comprising a closed main annular magnetic circuit on which an inner electric winding is coiled. A magnetic core, in the form of an open annular sector, is held in position at the periphery of the inner winding by peripheral bars. The assembly is covered by the outer electric winding. The magnetic core determines the value of the self inductance of the transformer.

Abstract: An ignition coil, for use particularly in the ignition of an automotive internal combustion engine, includes a central magnetic core member on each side of which is arranged at least one magnetic current return circuit member and two windings, one of which is a primary winding and the other a secondary winding, arranged coaxially around the central magnetic core member. The primary and secondary windings and the central magnetic core member are arranged within an inner casing and covered with synthetic resin. An outer casing encloses the assembly thus formed and surrounded wholly or partially by the magnetic current return circuit member.

Abstract: An inductive device comprising a ferromagnetic core which has two approximately U-shaped core halves (9, 11) connected together with their limbs (9', 11'; 9", 11") facing each other so that they enclose a core window (17). Each core half (9, 11) is constructed substantially from a packet of mutually parallel strips of an amorphous ferromagnetic material. Filling members (21', 21") consisting of a solid non-ferromagnetic material are placed between the free ends of each pair of facing limbs (9', 11'; 9", 11"), and in the space (23', 23") between the ends the filling members extend from the core window (17) in the outward direction over at most half of the width of the core limbs. A decrease of the magnetic permeability of the core material as a result of decreasing temperature is compensated by a decrease of the width of the air gaps (23', 23") between the free ends of the limbs (9', 11'; 9", 11").

Abstract: The transformer comprises a three-limbed magnetic core having two outer limbs each defining a central air gap. Two windings, an alternating current one and a direct current one, are wound around each outer limb. Primary and secondary windings are disposed on the center limb, the primary one being supplied with alternating current from a source, and the secondary one supplying with alternating current an external load. The two alternating current windings are connected in series and supplied with alternating current by the source, possibly through an additional winding wound around the center limb, while the two direct current windings are connected in series and supplied by the current in the alternating current windings rectified through a diode bridge. The current in the two direct current windings induces a magnetic flux in a closed circuit defined by the outer limbs.

Abstract: An ignition coil assembly for an internal combustion engine includes at least one first laminated core contained in a housing and having a plurality of first magnetic path connection end faces exposed to the inside of the housing, and at least one second laminated core having a plurality of second magnetic path connection end faces each opposing to one of the first magnetic path connection end faces through a thin gap. A primary coil and a secondary coil are wound on the second laminated core, and a plurality of soft waterproof layers are formed on inner walls of the housing to cover the first magnetic path connection end faces of the first laminated core.

Abstract: A magnetic wedge for use in an electromagnetic device, arranged at the opening portion of a core slot for receiving a winding, comprising a magnetic member consisting of a group of magnetic strips arranged in non-contact from one another and at a predetermined inclination angle for the depth direction of the core slot, and a plastic member for molding said magnetic member. Such a construction of the wedge permits the magnetic property at the opening portion of a core slot to be improved.

Abstract: Apparatus for sequentially igniting and serially operating a pair of electric discharge lamps from a source of AC supply voltage. The apparatus includes a transformer with a primary winding and first and second secondary windings mounted on a magnetic core having a slot under the second secondary winding. The first secondary winding has a high leakage reactance and the windings are serially connected with the secondary windings wound in opposition to one another. First and second capacitors are connected in series with the first and second lamps, respectively, to prevent the flow of DC current therethrough. By a novel choice of the ratios of the capacitance values of the second capacitor to the first capacitor and of the slot dimensions, superior operating characteristics for the apparatus are achieved.

Abstract: An inductor device having a ferromagnetic core with an airgap. The ferromagnetic core contains two U-shaped sections (1, 3) with their limbs (5, 7) directed towards each other. One pair of limbs directed towards each other is surrounded by a coil former (9) made of an electrically insulating material, on the inner surface of which is located a projecting element (13) at right angles to the longitudinal direction of the limbs. The projecting element extends between the ends of the limbs that are surrounded by the coil former and determines or defines the width of an airgap (15) between those ends. The ends of the other set of limbs pointing towards each other (5, 7) are placed directly one against the other.

Abstract: A storage coil for flux converters or low setting control elements is disclosed. The storage coil has a non-linear d-c bias characteristics associated with a ferrite core. The ferrite core may be a shell core, E core, RM core and U core, with an air gap formed between adjacent end faces of core parts, the adjacent end faces being oriented toward each other to provide a contact area without an air gap less than the overall cross-sectional area of the core and air gap of varying spacing occupying the area remaining between the contact area and the overall cross-sectional area.

Abstract: A single electromagnetic structure comprising a pair of assembled oppositely positioned pot cores, first and second winding means around each of the pedestals of the cores, and a flat magnetically permeable washer-like member positioned between the windings and spaced from the pedestals and the outer annular rim portions of the pot cores to define a pair of air gaps, whereby the apparatus functions like a transformer and an inductor in series with a winding of the transformer.

Abstract: A core shunt packet for reducing the telephone influence factor in a transformer of the type having a core formed from strips of magnetic material arranged in end-to-end relation forming a series of staggered gaps at one end of the core, the core shunt packets including one or more steel laminations mounted in an envelope, the envelope being mounted on the side of the core in a position to bridge the gap area on the core with a sheet of insulation located between the envelope and the side of the core.

Abstract: A circuit containing a ballast for one or more fluorescent lamps. The circuit includes a first inductor in series with a voltage input terminal and a first capacitor to form a series resonant circuit to provide a starting voltage to the lamps. A second, shunt inductors coupled between the first inductor and the capacitor and another input terminal of the circuit to eliminate the high Q of the series resonant circuit and prevent the first inductor from saturating. The inductors are mounted on the legs of an H-shaped core to provide inductive coupling between the inductors and allow a maximum winding area for the first inductor to reduce the series resistance of the lamp current path. The core also allows the shunt inductor to adjust power line power factor independently of lamp power factor. Improvements in system efficiency of up to 15% can be achieved over conventional core/coil type ballasts.

Abstract: A core for an inductor or transformer includes a number of concentric turns of a ferromagnetic strip material. An inner core portion (13) consists of a non-amorphous material and an outer core portion (27) consists of an amorphous material. The transition between the two core portions (13, 27) is formed by a welded joint between the overlapping outer (17) and inner (15) end portions of the outer turn of the inner core portion (13), and with the inner end portion (19) of the inner turn (33) of the outer core portion (27) disposed therebetween.

Abstract: The present invention relates to a core of magnetic amorphous alloy. A thin strip of such alloy is wound and then cut to provide, e.g., C-shaped pieces. A pair of C-shaped pieces is assembled to provide the core. Conventionally, the magnetic properties, e.g., the watt loss, of the core are impaired at the cut ends of a thin strip due to the formation of burrs.The present invention is characterized by providing the cut ends with a thickness substantially the same as the thickness of the non-cut portion of the thin strip and by polishing the cut ends substantially parallel to the major surface of the thin strip, thereby improving the magnetic properties of the core.

Abstract: An electrical transformer comprises a hollow form exhibiting high magnetic permeability and interior projections extending between separable halves of the form to provide a low magnetic leakage transformer core. Primary and secondary windings are disposed around the central projections. Furthermore, there is included means internal to the form for providing a lower permeability magnetic circuit shunt path. The internal shunt path means is typically either a cylinder or disc structure. A reduction in stray magnetic flux is desirable since it means that smaller, less expensive transformers may be constructed. The transformer of the present invention is particularly useful in electronic ballast circuits for gas discharge lamps because the magnetic shunt path acts as a current-limiting inductor. Moreover, since the transformers of the present invention do not generate external magnetic fields, flux shields are not required to maintain high efficiency.