Patent ID: 7791283
Filing Date: 2010-09-07
Classification: H05B

Abstract:
1. A discharge lamp lighting apparatus comprising a high voltage transformer with a discharge lamp connected to a secondary side thereof, a switching circuit performing a switching operation based on a frequency of a triangular wave outputted from a triangular wave generation circuit so as to drive a primary side of the high voltage transformer, and a resonance circuit formed on the secondary side of the high voltage transformer in which its capacitance component is constituted of only a parasitic capacitance, wherein: the switching circuit in pre-lighting of the discharge lamp is made to perform switching operations at a frequency around a series resonance frequency of the resonant circuit on the secondary side; the switching circuit in post-lighting of the discharge lamp is made to perform switching operations at a frequency around which a phase difference between voltage and current on the primary side becomes minimum; a symmetric signal is inputted into the switching circuit based on a signal produced by the triangular wave generation circuit and a symmetric rectangular wave voltage is outputted from the switching circuit; the triangular wave generation circuit is connected to a frequency changing means provided with a capacitor and a frequency switching means including a transistor, a first resistor, a second resistor connected in parallel to the first resistor and connected to a collector of the transistor and an inverter element connected to a base of the transistor, and the frequency of the triangular wave generation circuit is adjusted by the capacitor and the first and second resistors; the frequency of the triangular wave outputted from the triangular wave generation circuit in an unlighted period of the discharge lamp is determined by a capacitance of the capacitor and a combined resistance of the first and second resistors; and the frequency of the triangular wave outputted from the triangular wave generation circuit in a lighted period of the discharge lamp is determined by the capacitance of the capacitor and a resistance of the first resistor.