JPS54131367A - Flourescent lamp depreciation - Google Patents

Abstract

PURPOSE:To enable improved starting under the depreciation condition as the expected depreciation condition is maintained, by controlling conduit current by means of a phase control, and by setting a phase control angle which is behind a delay of the conduit current and is a head of a delay phase of a pre-heat current. CONSTITUTION:A phase angle of a conduit current phase circuit 13 is set between a delay phase of a conduit current, whose phase is behind a power source voltage, and a delay phase of a pre-heat current which is behind the power source voltage. When a depreciation switch 5 is opened, a trigger current flows to a triac 7 in a phase delay with each half cycle of the power source voltage, and the triac 7 turns on to flow a conduit current. It is held up to a delay phase of the next half cycle of the power source voltage, and a fluorescent lamp 4 is depreciated due to phase control of the conduit current. In the case of starting the fluorescent lamp 4 under a depreciation condition, the triac 7 turns on due to the phase being ahead of a delay phase of a pre-heat current, and thus, the triac 7 turns on fully, and the pre-heat current pre- heats sufficiently the fluorescent lamp without being phase-controlled.