| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that an additional polarity inversion signal is not inserted in proper timing while the time length of an interval between polarity inversion signals varies depending on situations.SOLUTION: As a basic operation, a polarity inversion control circuit gives a polarity inversion instruction so that the polarity of an inverter is reversed every time polarity inversion timing notified by a polarity inversion signal is recognized, and the circuit counts the number of continuous appearances of a normal polarity inversion interval period Np in which the interval of adjoining polarity inversion timing is not more than the upper limit value Tsup of a polarity inversion interval desirable for a discharge lamp. The circuit memorizes Npm as the maximum value of the number of continuous appearances Np when an abnormal polarity inversion interval period appears in which the interval of the adjoining polarity inversion timing is longer than the upper limit value Tsup of the polarity inversion interval, and thereafter determines that the abnormal polarity inversion interval period has started on receiving the polarity inversion signal in which the number of continuous appearances Np becomes equal to Npm, and gives an additional polarity inversion instruction. |
