Sanken Electric Co., Ltd.

Hironobu Sou

Masaki Kanazawa

Hideki Nakamichi

Nanjou Aoike

A lighting system for a fluorescent lamp includes an inverter circuit having a pair of outputs between which is connected a resonant circuit of an inductor and a capacitor in series, with the discharge lamp connected in parallel with the capacitor. An inversely frequency dependent voltage is applied between the lamp electrodes according to a predefined resonance characteristic. During a preheat period, which precedes a lightup period during which the lamp is to be lit up with the commencement of an electric discharge between the lamp electrodes, the voltage is made lower in the first half than in the second, thereby averting the sudden flow of a large preheating current through the filamentary lamp electrodes.

Incrementally preheating and lighting system for a discharge lamp

A lighting system for a fluorescent lamp includes an inverter circuit to which is connected a load circuit including a resonant circuit of an inductor and a capacitor in serial connection, with a lamp connected in parallel with the capacitor. An inversely frequency dependent voltage is applied between the lamp electrodes according to a predefined resonance characteristic such that the resonance frequency is less than a discharge start frequency at which the lamp is to start glowing. For lighting up the lamp the frequency of the inverter output voltage is changed from a first frequency that is higher than the discharge start frequency to a second frequency that is less than the resonance frequency. If the lamp accidentally goes off, the current flowing through the load circuit will advance out of phase with the inverter output voltage, possibly resulting in the destruction of the inverter switch or switches due to overcurrent. This danger is precluded by constantly monitoring the phase of the load current and, in event the load current is found to be in phase advance, by making the inverter output frequency higher than the resonance frequency of the resonant circuit and thereby delaying the phase of the load current.

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Tokorozawa, Japan

Hironobu Sou