| 摘要 |
PURPOSE:To suppress fluctuation of lamp current by providing a power source fluctuation compensating section which changes the changing rate of one switching element on-period, which follows the change of the other switching element on-period, in response to power source voltage fluctuation. CONSTITUTION:The first and the second switching elements Q1 and Q2 are connected in series to both terminals of DC source E, and the element Q2 is made to be on and off by a separately exited signal. The element Q1 being made to be on and off by the output of the secondary winding n2 of an inductance L1, the elements Q1 and Q2 are alternately made to be on and off so as to light a discharge lamp (La) by high frequency. Then the on-period of the element Q1 is detected by an on-period detecting section A, during the off-period, the separately exciting signal, which makes the element Q2 to be on, is generated by a separately exiting signal generating section B. The on-period of the element Q2 is changed based on the on-period of the element Q1 by an on-period control section C, and the changing rate is changed by a power source fluctuation compensating section D in response to power source voltage fluctuation. Thereby it is possible to suppress the fluctuation of current in the lamp La caused by characteristics of respective elements, thermal characteristics and the fluctuation of the power source. |
