DISCHARGE LAMP LIGHTING DEVICE, AUTOMOTIVE HIGH-INTENSITY DISCHARGE LAMP LIGHTING DEVICE, AUTOMOTIVE HEADLIGHT DEVICE, AND CAR

1 . A discharge lamp lighting device comprising a controller configured to perform an abnormality judgment process of judging whether or not abnormality has occurred based on a measured value of a driving voltage defined as an AC voltage applied to a discharge lamp,

wherein:

the controller is configured to, in the abnormality judgment process, judge whether or not an asymmetric state in which the driving voltage lacks symmetry has occurred over a predetermined period; and

the controller is configured to, upon concluding that the asymmetric state has occurred over the predetermined period, conclude that the abnormality has occurred.

2 . The discharge lamp lighting device as set forth in claim 1 , wherein

the controller is configured to, upon acknowledging that an absolute value of one of a first measured value defined as the measured value obtained before a reversal of polarity of the driving voltage and a second measured value defined as the measured value obtained after the reversal of polarity of the driving voltage is greater than an absolute value of the other of the first measured value and the second measured value, conclude that the asymmetric state has occurred.

3 . The discharge lamp lighting device as set forth in claim 2 , wherein

the controller is configured to:

calculate a proportion of a larger one of the absolute values of the respective first and second measured values to a smaller one of the absolute values of the respective first and second measured values; and

upon acknowledging that the proportion is not less than a threshold, conclude that the asymmetric state has occurred.

4 . The discharge lamp lighting device as set forth in claim 3 , wherein

the threshold is not less than 1.5.

5 . The discharge lamp lighting device as set forth in claim 2 , wherein

the controller is configured to:

calculate a difference between the absolute values of the respective first and second measured values; and

upon acknowledging that an absolute value of the difference is not less than a threshold, conclude that the asymmetric state has occurred.

6 . The discharge lamp lighting device as set forth in claim 5 , wherein

the threshold is not less than one-half of a rated lamp voltage of the discharge lamp.

7 . The discharge lamp lighting device as set forth in claim 1 , wherein

the controller is configured to, upon acknowledging that the asymmetric state continues for the predetermined period, conclude that the asymmetric state has occurred over the predetermined period.

8 . The discharge lamp lighting device as set forth in claim 7 , wherein

the predetermined period has a length equal to that of a start-up period of the discharge lamp.

9 . The discharge lamp lighting device as set forth in claim 7 , wherein

the predetermined period has a length not less than 10 seconds.

10 . The discharge lamp lighting device as set forth in claim 1 , wherein

the controller is configured to, upon acknowledging that the number of times of occurrence of the asymmetric state is not less than a predetermined number of times before a passage of a prescribed period, conclude that the asymmetric state has occurred over the predetermined period.

11 . The discharge lamp lighting device as set forth in claim 1 , wherein

the discharge lamp lighting device further comprising a lighting circuit unit having a function of applying an AC voltage to the discharge lamp, and

the controller is configured to control the lighting circuit unit to adjust power supplied to the discharge lamp.

12 . The discharge lamp lighting device as set forth in claim 11 , wherein

the lighting circuit unit comprises:

a power converter configured to generate DC power by use of power from an external power source;

an inverter configured to apply an AC voltage to the discharge lamp by use of the DC power generated by the power converter;

a voltage detector configured to measure a voltage applied to the discharge lamp; and

a current detector configured to measure a current flowing through the discharge lamp,

the controller is configured to adjust the DC power generated by the power converter based on a measured value of the voltage detector and a measured value of the current detector.

13 . The discharge lamp lighting device as set forth in claim 11 , wherein

the controller is configured to, upon concluding that the abnormality has occurred, decrease power supplied to the discharge lamp down to a predetermined value.

14 . The discharge lamp lighting device as set forth in claim 13 , wherein

the controller is configured to gradually decrease power supplied to the discharge lamp.

15 . The discharge lamp lighting device as set forth in claim 11 , wherein

the lighting circuit unit has a function of applying a DC voltage to the discharge lamp, and

the controller is configured to, upon concluding that the abnormality has occurred, control the lighting circuit unit in such a manner to supply to the discharge lamp a DC voltage having the same polarity as that corresponding to larger one of the absolute values of the respective first and second measured values.

16 . The discharge lamp lighting device as set forth in claim 1 , wherein

the controller is configured to start the abnormality judgment process after the discharge lamp is changed from a state in the start-up period to a state in a steady lighting period.

17 . An automotive high-intensity discharge lamp lighting device defined by the discharge lamp lighting device according to claim 1 , and configured to light a high-intensity discharge lamp.

18 . An automotive headlight device comprising:

a discharge lamp; and

the discharge lamp lighting device according to claim 1 ,

wherein the discharge lamp lighting device is configured to light the discharge lamp.

19 . A car comprising the automotive headlight device according to claim 18 .