The present invention relates to an operating apparatus of discharge lamp. More particularly, the present invention relates to an operating apparatus of discharge lamp which is fed a phase-controlled alternating current (ac) voltage to adjustably control (dim) the brightness of a discharge lamp (e.g., a fluorescent lamp).
Advantages of fluorescent lamps over incandescent lamps are their higher efficiency and longer life span. Accordingly, various fluorescent lamps have been extensively used as luminaires suitable for household use. Particularly, the compact self-ballasted fluorescent lamp is replaceable directly with a conventional incandescent lamp. Because of this, the compact self-ballasted fluorescent lamp has lately attracted attention and has been now used widely. Recently, there has been a demand for adjustably controlling the brightness of fluorescent lamps in the same way as incandescent lamps. To meet this need, dimmable fluorescent lamps also have been developed.
In a typical technique of accomplishing dimming of the incandescent lamp, a phase-controlled ac voltage is input for incandescent lamp dimming. On the other hand, compact self-ballasted fluorescent lamp dimming requires the provision of a ballast circuit. The ballast circuit is fed a phase-controlled ac voltage to accomplish fluorescent lamp dimming. One example of an operating apparatus of discharge lamp of the type which is fed a phase-controlled ac voltage to accomplish fluorescent lamp dimming, is shown in JP Kokai Publication No. H11-111486.
Such a published operating apparatus of discharge lamp has a sensor means for detecting the conduction period of a phase-controlled ac voltage to be input and an inverter ballast circuit capable of variable output, wherein the output of the inverter ballast circuit is controlled according to the signal from the sensor means so as to vary the brightness of the fluorescent lamp. The sensor means provides a pulse signal proportional to the conduction period. If the conduction period is long, then the inverter ballast circuit will give an increased output to increase the brightness of the fluorescent lamp. On the other hand, if the conduction period is short, then the inverter ballast circuit will give a decreased output to decrease the brightness of the fluorescent lamp.
However, a conventional operating apparatus of discharge lamp of the type described above is constructed to control the light output of a fluorescent lamp according to a length of the conduction period of the input phase-controlled ac voltage. Accordingly, the light output varies substantially linearly with respect to the conduction period (FIG. 8). On the other hand, when a phase-controlled ac voltage is fed to an incandescent lamp, the light output varies non-linearly with respect to the conduction period (FIG. 9). The reason for such non-linear light output variation is that an effective value of the voltage that is fed to an incandescent lamp varies with respect to the conduction period as shown in FIG. 10.
Accordingly, when an operating apparatus of discharge lamp of the above-described conventional type is applied to compact self-ballasted fluorescent lamps, the light output with respect to the conduction period varies differently from the incandescent lamp. This may often cause a user to feel something incongruent for such light output.
Bearing in mind the above problem, the present invention was made. Accordingly, an major object of the present invention is to provide an operating apparatus of discharge lamp capable of accomplishing the discharge lamp dimming much similar in light output variation to incandescent lamp dimming.
The present invention provides an operating apparatus of discharge lamp comprising (a) AC/DC converter means for converting an ac voltage into a dc voltage, (b) DC/AC converter means for converting a dc output voltage of the AC/DC converter means into a high frequency ac voltage, (c) a discharge lamp coupled to an output terminal of the DC/AC converter means, and (d) controller means by which the output of the DC/AC converter means is made variable according to an integrated value of the ac voltage based on a half cycle thereof.
In an embodiment of the present invention, the controller means has an arithmetic part for performing arithmetic operations to calculate from the integrated value an approximate average value in one cycle and a control part by which the output of the DC/AC converter means is made variable according to an output signal level of the arithmetic part.
Preferably, the controller means further has characteristic detector means for detecting a lamp characteristic of the discharge lamp.
Preferably, the characteristic detector means detects at least one of a lamp voltage, lamp current, lamp power, and light output as the lamp characteristic.
In an embodiment of the present invention, the controller means has a function of causing the output frequency of the DC/AC converter means to vary.
In an embodiment of the present invention, the operating apparatus of discharge lamp is a compact self-ballasted fluorescent lamp with a base in which a ballast circuit including at least the AC/DC converter means, the DC/AC converter means, and the controller means and the discharge lamp are integrally formed.