US 2010/0072908 A1Published application

Discharge lamp lighting device

AssigneeTabuchi Electric Co., Ltd.

InventorHirofumi Konishi

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Abstract

There has conventionally been provided a discharge lighting device capable of performing dimming control of a hot cathode type discharge lamp. As a tube current is decreased, 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. The conventional device requires power supplies for controlling the tube current of the hot cathode type discharge lamp and for controlling a filament current, and has therefore a problem that a circuit becomes complicated, and the number of parts is increased, resulting in an increase in cost. In order to solve the above-described problem, an oscillation control circuit for determining a frequency with time constant of R and C; a L-C series resonant circuit connected to a half-bridge circuit operating at the frequency; and a circuit in which one ends of hot cathode filaments at both ends of a hot cathode type discharge tube are respectively connected in parallel with a resonant capacitor, and a capacitor is further connected in series to other ends of the filaments at the both ends of the hot cathode type discharge tube to perform lighting are provided, and nonstep dimming of the tube current is achieved by using a variable capacitance diode to change an oscillation frequency upon application of a DC dimming control voltage.

Claims9

Dependent claims

A discharge lamp lighting device having:

an oscillation control circuit for determining a frequency with time constant of R and C;
a L-C series resonant circuit connected to a half-bridge or a full bridge circuit operating at said frequency;
and a circuit in which one ends of hot cathodes (filaments) at both ends of a hot cathode type discharge tube are respectively connected to both ends of a resonant capacitor, and a capacitor is further connected in series to other ends of the filaments at the both ends of the discharge tube to perform lighting;
whereby (nonstep dimming) of a tube current is achieved by changing the oscillation frequency with a DC dimming control voltage by use of a voltage variable capacitor (variable capacitance diode) as a capacitor for determining the frequency of the oscillation control circuit, wherein
one-converter power supply configuration is employed;
by simultaneously changing the tube current and a filament current of the hot cathode type discharge lamp, as the tube current is decreased upon dimming, the filament current is increased to enable a reduction of a filament temperature to be prevented and stable discharge to be maintained;
simultaneously with this, the capacitor for determining the oscillation frequency of the oscillation control circuit is configured by a plurality of parallel-connected capacitors (including a variable capacitance diode);
and
by switching between these capacitors, a sufficient preheat current is ensured, and stable operation is performed.

6 more elements

Dependencies are inferred from the claim text.