| 摘要 |
PURPOSE:To reduce the size and costs as well as to simplify the structure by enabling operation of an inverter circuit with an optimum mode according to the state of a discharge lamp circuit on the basis of the output of a judging circuit. CONSTITUTION:There are provided a judgement circuit 4 wherein a test mode period is set during the preheating mode period for preheating discharge lamps DL1, DL2, from throw-in of power and the oscillation frequency of an inverter circuit 1 is set during the test mode being shifted from the resonance frequency of a current resonating circuit so that the state of a discharge lamp circuit 3 is judged with the operation condition change of resonator system, an oscillation control circuit 5 for operating an inverter circuit 1 with an optimum mode according to the state of the discharge circuit 3. It is thus possible to detect the state of the discharge lamp circuit 3 surely without applying any stress to switching elements Q1, Q2 and to make the circuit configuration simple as well as to reduce the size and costs easily since the state of the discharging circuit 3 is detected according to the operation state change of the resonator system. |
