The invention relates to a planar transformer arrangement for an electric circuit located on a circuit board. The arrangement comprises (a) a first circuit board (PCB1) on which said electric circuit has been implemented, (b) a supplementary circuit board piece (PCB2), (c) a primary winding which comprises at least one substantially planar conductive pattern formed on a circuit board, (d) a secondary winding which comprises at least one substantially planar conductive pattern formed on a circuit board, and (e) a transformer core (F1, F2) which surrounds the primary and secondary windings at least partially. To create an inexpensive but efficient transformer structure suitable for use in an automatic manufacturing process, both the primary and the secondary windings have been formed on the supplementary circuit board piece (PCB2).

A planar magnetic device with vertically oriented coil windings having a cross-section of a core with a torroidally-shaped winding structure taken transverse to the plane of the winding structure having two adjacent "winding windows" where the coils are present. One or more gaps in the core materials surrounding the windings store most of the energy generated by the inductor. The gap of height of at least one half the height of the winding structure is confined to the area between the winding cross-sections. Furthermore, in another aspect of the invention the gap is filled with a multi-layer structure of an alternating mono-layer of equally sized ferrite particles and a layer of synthetic resin.

An inverter transformer is provided which can turn on a plurality of cold cathode fluorescent lamps (CFLs) with a minimized increase in the number of components, thereby reducing costs. The inverter transformer comprises a plurality of bobbins for windings. The plurality of bobbins each having a secondary winding wound thereon and having a bar-shaped inner core inserted therein are connected to one another for integration, and a primary winding is wound in common on the bobbins connected together. A plurality of inner cores and a rectangular frame-shaped outer core are magnetically coupled with each other with non-magnetic sheets interposed therebetween to provide a predetermined leakage inductance. A plurality of CFLs can be turned on with only one outer core, thereby reducing the number of components, downsizing the device, and reducing the cost.

A magnetic assembly is constructed comprising a first core portion, a second core portion, and a winding assembly. The first and second core portions each include a base portion and a plurality of projections extending from the base portion. The winding includes a plurality of stacked layers having conductive paths applied to their surfaces. The winding is constructed with a bore, wherein each conductive path encircles the bore. A number of the stacked conductive layers form a primary winding, and a number of the stacked conductive layers form a secondary winding. The winding is disposed over the first core portion in a manner so that a projection engages the opening of the winding to provide magnetic coupling of winding and core. The second core portion is disposed over the first core portion to form a closed magnetic circuit through and around the winding.

Transformer comprises a core (K1, K2), a primary winding (W1) and at least one secondary winding (W2), which are arranged as conductors on one or more layers of a flat carrier, and a coil former with a chamber system having chambers (C1, C2), which accommodate the layers with the windings (W1, W2). At least one of the chambers (C1, C2) is closed at least in regions, with the result that long distances for creepage paths are obtained. As a result of this, it is possible to adhere to existing safety regulations for the mains power supply isolation even with very compact dimensions and/or with full utilization of the width available for the conductor tracks. The chamber system can be formed from two or three plastic parts (P1, P2, P3) by mating. The layers with the conductor tracks are routed laterally out of the chamber system in order to make contact with terminals. In an advantageous refinement, webs with metallized slots are arranged on walls of the chamber system, in order to make contact with the conductor tracks (L). The slots are, for example, notched or trough-shaped depressions in which the carrier layers latch into place and are held thereby. The electrical contact afforded by the slots can be additionally supported by a solder-paste application with subsequent soldering. The lateral contacts mean that plated-through holes are avoided in the case of the carrier layers, with the result that the latter can be produced significantly more inexpensively. By virtue of the chamber system, it is possible for the openings in a core, for example an E/E or E/I core, to be utilized significantly better if the transformer has to comply with a sufficient insulation strength, such as in the case of mains power supply isolation, for example.