| 摘要 |
PURPOSE:To prevent erroneous switching of an oscillation frequency of an inverter circuit. CONSTITUTION:High voltage is impressed upon a high pressure discharge lamp DL, and the lamp is started, and is lighted in a high frequency. An electric current detecting circuit 1 detects an electric current flowing to the high pressure discharge lamp DL. A starting discriminating circuit 4 detects a large electric current flowing at starting time of the high pressure discharge lamp DL from output of the electric current detecting circuit 1, and discriminates the starting of the high pressure discharge lamp DL. When discriminated that the high pressure discharge lamp DL is started, a lighting discriminating circuit 2 detects a lamp electric current at lighting time of the high pressure discharge lamp DL from output of the electric current detecting circuit 1, and starts discriminating operation on a lighting condition of the high pressure discharge lamp DL. Until the starting discriminating circuit 4 discriminates that the high pressure discharge lamp DL is started, an inverter circuit INV is oscillated in a frequency (f2) at unlighted time of the high pressure discharge lamp DL. After the starting is discriminated, it is oscillated in a frequency (f1) at the lighting time. After the inverter circuit is oscillated and operated in the second frequency, the inverter circuit INV is oscillated in the frequency (f2) when discriminated by the lighting discriminating circuit 2 that the high pressure discharge lamp DL is put in an unlighted condition. |
