1. Field of the Invention
The present invention relates to an electronic track lighting system, and in particular, to a lighting system which lights a lamp load such as a halogen lamp at a high frequency by an inverter circuit using an electric power fed via a power track.
2. Description of the Related Art
Conventionally, an inverter circuit disclosed in Japanese Patent No. 2770337 has been well known as an inverter circuit for lighting a halogen lamp, and the disclosed circuit has a configuration as shown in FIG. 17. In the inverter circuit, a portion surrounded by a broken line shown in FIG. 12 is provided as a unit. The inverter circuit is built in a transformer unit A and is used together with a lamp load 3 in the form as shown in FIG. 13. As shown in FIG. 14, the electronic transformer unit A is connected to a power track 6 mounted on a ceiling via a power track connective portion 4 provided on an upper portion thereof. A commercial alternating current voltage of AC 100V is supplied to the electronic transformer unit A through the power track 6. A lamp unit 5 suspended from a lower portion of the electronic transformer unit A is mounted with a lamp load 3 such as a halogen lamp or the like.
For example, such a luminaire (lighting equipment) is used for showcase (display case) lighting, light up of show windows, and it is strongly desired that the electronic transformer unit A connected to the power track 6 is miniaturized. However, the prior art employing the aforesaid 100V power track system has the following problem. More specifically, as seen from a circuit shown in FIG. 15, each of a plurality of the electronic transformer units A includes a filter circuit for reducing a power supply feedback noise and a protective circuit for protecting a circuit when a lightning surge is applied, respectively. Therefore, size of the electronic transformer unit A becomes large.
A 12V power track system as shown in FIG. 16 is often used in general, and is constructed in the following manner that a secondary side (output side) of an output transformer T1 of the electronic transformer unit A is connected to the power track 6, and a plurality of 12V mini-halogen lamps are connected to the power track 6 via a lamp unit to be lit. In this case, the power track 6 is supplied with a high frequency voltage of 12V transformed from a commercial supply voltage of AC 100V by the electronic transformer unit A.
Moreover, in U.S. Pat. No. 5,180,952, proposed is a method of supplying, to the power track system, a voltage which is converted from a commercial power supply voltage into a high frequency voltage to downsize each unit.
In the AC 100V power track system as shown in FIGS. 14 and 15, the electronic transformer unit A must be connected one by one with the power track. Therefore, depending upon a size of the electronic transformer unit A connected to the power track 6, there is a limitation of the number of electronic transformer units A capable of being connected to a predetermined length of the power track. Conversely, comparing to the 12V power track system, a current flowing through the power track 6 is less, and thus the AC 100V power track system has a merit such that a voltage drop by an impedance of the power track 6 is smaller than the 12V power track system and does not affect brightness of the light unit.
On the other hand, in the high frequency 12V power track system shown in FIG. 16, one electronic transformer unit A is shared with a plurality of halogen lamps 3. Therefore, each halogen lamp 3 is connected to the power track 6 by only lamp unit 5. As a result, the high frequency 12V power track system has merit such that the whole of lighting system can be miniaturized. However, as described above, a voltage is low, that is, 12V, and thus a current flowing through the power track 6 is 9 times as much as the AC 100V power track system. Therefore a voltage drop by an impedance component of the power track 6 is large, and when the long power track is used, the lamp unit far from the transform unit A becomes dark. Moreover, in attaching/detaching the lamp unit 5 to/from the power track 6, there is the following problem. Since a current flowing through a connective fitting 4 with the power track 6 is large, an arc is generated at the attaching or detaching.
The present invention has been made in view of the above problems in the prior art. It is therefore an object of the present invention to provide a lighting system which can suppress a current flowing through a power track so that no arc is generated between a connective metal fitting and the power track when attaching and detaching a lamp unit.