Importance

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Abstract

A lighting circuit for a vehicular discharge lamp has a DC voltage booster circuit, a control circuit, and a voltage drop detector. The booster circuit boosts an input voltage from a DC voltage input terminal to provide an output voltage to be applied to the discharge lamp. The control circuit functions for varying the output voltage of the DC booster circuit to effect lighting control including constant power control of the discharge lamp. The voltage drop detector detects a DC input voltage applied to the booster circuit. In response to a signal received from the voltage drop detector in accordance with a drop of the DC input voltage, the control circuit performs voltage boosting control to set power supplied to the dicharge lamp lower than the rated power. It is therefore possible to suppress an increase in current consumption and a consequent increase in generated heat when the DC input voltage drops. Further, the lighting circuit for a vehicular discharge lamp has a protection circuit which cuts off the supply of the DC input voltage to the DC voltage booster circuit when it is detected that the DC input voltage has dropped too low to maintain the lighting of the discharge lamp, and allows the DC input voltage to be supplied again to the booster circuit when the DC input voltage has been restored to or greater than a predetermined value. It is therefore possible to prevent the circuit elements from being deteriorated or destroyed due to an abnormal reduction in DC input voltage.

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First Claim