1.  Field of the Invention
The present invention relates to a fluorescent lamp ballast.  More particularly, the present invention relates to a ballast structure for providing an advanced connection leads management through a minor modification to existing ballast enclosure. 
2.  Discussion of Related Art
Fluorescent lamps are replacing more old incandescent fixtures due to their efficiency in converting a higher percentage of the electric power into light, which is more even and diffused in many circumstances.  In order to operate a tubular form of a fluorescent bulb, a fluorescent fixture normally includes a ballast for limiting current through a thin ionizing gas in vacuum and a starter to supply power for starting the bulb to generate ionizing electrons.  Ballasts come in discrete cases and need a firm mounting on a hidden side of the fluorescent fixture or a junction box.  The ballast, in an electronic design, comprises on a printed circuit board (PCB) active and passive components surface mounted on thru-holes formed in PCB including capacitors, a choke coil, transistors, at least one transformer and resistors all housed in a secure metal enclosure so that it is not opened.  In case of failure, it is not a repairable component but to be simply replaced as a whole.  For such replacement, wires must be relocated into the new ballast. 
However, different fixture specifications for the respective lamp types may require different lead directions such as longitudinal versus perpendicular directions of the wires in order to reinstall the ballast.  Because conventional ballasts have set terminal locations to connect with wires it has been attempted to employ adaptors to mount one type of ballast to an incompatible fixture.  To avoid these wire management problems, electricians had to prepare two groups of ballasts, which are essentially same besides the wire lead directions. 
In an effort to reduce the inventory effort, modifications to the ballast enclosure as well as the circuitry itself have been made. 
As shown in FIG.  1, a lamp ballast 1 has an enclosure 2 that comprises a top case 3 and a base case 4 of sheet metal.  Inside of the enclosure 2, connected components on PCB (printed circuit board) are mounted and a dielectric sheet liner may be interposed between the components and the case 3 for insulation.  Top case 3 has notched bracket portions 5 for mounting on a section 6 of lamp fixture or an adapter plate.  The illustrated type of ballast is found available under the name ‘SmartMate’ by Advance Transformer Co., Rosemont, Ill. having a side connection set of lead wires 7.  This ballast permits an alternative top connection set of lead wires 8 to be provided.  Each set of wires 7 or 8 is connected to an input power terminal strip 9 of ballast 1 and an output lamp terminal strip 10.  Conventionally, side lead wires 7 have been possible by side opening of the terminal strips 9, 10 and top lead wires 8 needed top opening of the terminal strips 9, 10.  Of different possible mounting configurations, many surface mounted lamp fixtures on ceiling may need side lead wires while recessed lighting fixtures may require top lead wires mounted on a junction box, which is in turn mounted on the recessed fixture. 
This ‘dual-entry’ connection of the prior art ballast sought to reduce the unnecessary inventory management to carry more ballast models from purchase to installation.  However, such reduction only comes with the setback of requiring a specialized component of 2-conductor PCB terminal strip, which needs disposal of the existing inventory of single conductor strips for replacement.  In addition, the enclosure always leaves unnecessary openings
A solution is necessary to keep the currently established construction of ballast circuit and be able to have the connection wires lead in one of the two appropriate directions, which are vertical and horizontal without a significant redesign of the ballast. 
In view of the foregoing deficiency of the state of the art ballast enclosures, an object of the present invention is to provide a lamp ballast with a novel enclosure for allowing the connection wires to have two selectable lead directions requiring no changes in the existing ballast circuit.