Importance

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Abstract

A discharge lamp lighting apparatus according to this invention comprises: an inverting circuit for converting a DC input into a high frequency output; a load circuit which is connected to the inverting circuit and is constructed by a plurality of discharge lamps; a detecting resistor connected between a terminal of the inverting circuit and a ground; an integrating circuit for integrating a voltage generated in the detecting resistor; an operational amplifier which receives an output of the integrating circuit as a negative input, receives a predetermined target value as a positive input, and performs an error amplification; a driver for controlling a switching frequency of the inverting circuit on the basis of an output of the operational amplifier; a frequency detecting comparator which inputs the output of the operational amplifier and whose output value is switched in the case where a frequency converted at an input value exceeds a predetermined value; a control circuit for switching an operating state of the driver depending on the output value of the frequency detecting comparator; and a latch circuit for holding the operating state switched by the control circuit in the case where the converted frequency exceeds the predetermined value. Therefore, even if a plurality of lamps are mounted, the circuit can be protected from a life ending lamp without performing a life ending detection for each lamp. The burden of the inverting circuit can certainly be detected and a protection can be performed, since the life states of a plurality of the lamps are detected in total.

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First Claim