There has conventionally been provided a discharge lighting device capable of performing dimming control of a hot cathode type discharge lamp such as a fluorescent lamp. In the case of dimming, as a tube current is decreased (dimming level is increased), a filament temperature is decreased, and as the tube current is further decreased, discharge cannot be maintained, which in turn causes moving striations and flickering.
A conventional device addressing such a problem is described in, for example, Patent document 1. As illustrated in FIG. 13, the conventional device is configured to include four power supplies including an inverter power supply 1 for lighting, a DC-DC power supply 3 for lighting, a DC-DC power supply 4 for preheating, and an inverter power supply 2 for preheating filter. Dimming is performed by varying an output voltage of the DC-DC power supply 3 for lighting. Control of a filament current is performed by connecting the output voltage of the DC-DC power supply 3 for lighting to a feedback circuit 5 for the DC-DC power supply 4 for preheating, and varying an output voltage of the inverter power supply for preheating 2 in proportional to a level of the dimming.    Patent document 1: Japanese Unexamined Patent Publication No. 1995-211478    Patent document 2: Japanese Unexamined Patent Publication No. 2001-357994
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