| 摘要 |
PROBLEM TO BE SOLVED: To recognize an abnormality of source voltage without using a source voltage detection circuit and the like. SOLUTION: A dimming circuit 46 outputs a dimming signal by taking in a pulse width modulation signal PS. A lamp current detection circuit 44 outputs a current detection signal by detecting a lamp current flowing in an electric discharge lamp 41. The current detection signal is supplied to a first amplifier 45, and the dimming signal is supplied to each of second and third amplifiers 47 and 48. A second amplifier output is supplied to the first amplifier. An adder 49 is provided. In the adder 49, a first amplifier output V2- OUT and a third amplifier output V3- OUT are added to each other, and the added output V4- OUT is supplied to a comparator 51. The comparator compares the added output with a reference voltage Vref, and when the adder output is smaller than the reference voltage, a high level signal is supplied to an oscillation control part 50. Accordingly, the oscillation control part controls a drive circuit 37 and extinction fixing of the electric discharge lamp is performed, thereby informing the abnormality of the source voltage. |
