The invention relates to a power supply unit for the supply of low power loads, in particular low voltage loads such as, for example, fluorescent lamps having a screw base, comprising input-side power connections and output-side load connections as well as a capacitor arrangement of large capacitance, in particular an electrolytic capacitor arrangement.
Screw base fluorescent lamps are nowadays widely used, because they require substantially less energy for comparable illuminating power in comparison to conventional filament lamps. Due to the screw base, an exchange of the filament lamps with such fluorescent lamps is in principal easily possible.
However, the exchange is often not possible due to the fact that the space requirement for screw base fluorescent lamps is very large in comparison to the conventional screw base filament lamps, especially in the region near the screw base. This stems from the fact that conventional screw base fluorescent lamps possess power supply units of comparably large volume, which must be accommodated in housings of corresponding large dimensions adjoined to the screw base.
An object of the present invention is to provide an electrical power supply unit that has a particularly small spatial requirement and, for application in screw base fluorescent lamps, offers the possibility of constructing these lamps in a substantially more space-saving manner so that the substitution of conventional screw base filament lamps with screw base fluorescent lamps is made substantially easier.
This and other objects are achieved by the present invention which provides a power supply unit for the supply of low voltage loads for fluorescent lamps, comprising a screw base, input-side power connections and output-side load connections, and an electrolytic capacitor arrangement of large capacitance. The capacitor arrangement is relatively flat and has a relatively large cross-section and a relatively small height perpendicular to a plane of the large cross-section.
The present invention recognizes that the spatial requirement of a power supply unit of the initially described kind is influenced to a high degree by the capacitor arrangement used. Whereas in conventional power supply units standard capacitors are typically used which have height, width, and length dimensions of a similar order of magnitude, the present invention employs capacitors having a particular construction, i.e. capacitors which are constructed in the manner of a flat piece. This offers the advantage that the flat piece forming the capacitor can also serve as a supporting or co-supporting part for the other components of the electrical power supply, whereby a particularly compact construction is made possible.
Additionally, the cross-section of the capacitor arrangement constructed as a flat piece can be tailored to the form of the available accommodating space. For the example of a screw base fluorescent lamp, the cross-section of the flat piece-shaped capacitor arrangement can then be tailored to the cross-section of the screw base or to the base area of the holder for the fluorescent lamp parts. Thereby, a particularly compact screw base fluorescent lamp can be realized, as is shown further below.
In accordance with a preferred embodiment of the invention, the capacitor arrangements can comprise layered electrodes, having electrode surfaces which are substantially parallel to the plane of the cross-section. This construction offers the advantage that there exist practically no limitations with regard to the form of the capacitor arrangement's cross-section and correspondingly, a particularly good matching to the relevant conditions in use is possible.
In certain embodiments, a capacitor arrangement is used having wound electrodes, wherein the electrode surfaces are disposed substantially perpendicular to the plane of the cross-section of the flat piece-like capacitor arrangement.
In certain embodiments, the power supply unit will also comprise a transformer or choke coil arrangement. The windings of the transformer or choke coil arrangement are accommodated as well as the capacitor arrangement in a common housing constructed from several pieces. In certain embodiments, the transformer or choke coil arrangement is disposed in approximately the same plane as the capacitor arrangement.
However, it is also possible and advantageous to provide the windings of the transformer or choke coil arrangement at an end face of the capacitor arrangement.
By accommodating the transformer or choke coil arrangement as well as the capacitor arrangement in a common housing, a module is created unifying the large parts of the power supply unit, so that a very compact manner of construction is possible.
Certain embodiments of the invention provide the housing with an axial channel which is approximately perpendicular to the large cross-section of the flat piece-like capacitor arrangement, this axial channel traversing the housing from one end face to the other end face.
With the tubular axial channel, by means of which the housing obtains a ring-like structure, it is taken into account that the power supply unit of screw base fluorescent lamps is expediently disposed spatially and axially between the screw base and the light-producing lamp parts and must therefore be electrically connected both to the screw base and to the light-producing lamp parts. The corresponding wiring can be laid in the axial channel. This also applies to the electrical connections between the transformer or choke coil arrangement, and the capacitor arrangement as well as further electronic components of the power supply unit.
The parts of the capacitor arrangement housing can be optionally manufactured from magnetizable material, in particular ferromagnetic material, in order to create additional electrical inductance in the electrical power supply, as is desired for many types of applications. In this manner, the capacitor arrangement housing also adopts the function of an electrical or electronic component.