| 摘要 |
PURPOSE:To let enough heating currents flow to a discharge lamp so as to extend the life of the lamp by providing a means which changes over a threshold between the first standard value and the second standard value being different from each other. CONSTITUTION:If a changeover switch SW is fallen on to the first standard voltage REF side so as to compare the first standard voltage REF with the detecting voltage of an impedance R for current detection by a comparator IC, the starting voltage enough for a discharge lamp L to start up can not be obtained, and the currents flow to the filament of the discharge lamp L, so the filament of the discharge lamp L is heated. And after the filament is heated to enough level at which the life is not shortened, the changeover switch SW is fallen to the second standard voltage REF side so as to compare the second standard voltage REF with the detection voltage of the impedance R for current detection by the comparator, where-upon the discharge lamp L becomes normal lighting conditions. That is, by changing over the threshold for turning off a switch element Q to a lower value (the first standard value) in advance, enough heating currents are left flow to the discharge lamp at the time of start-up of the discharge lamp L whereby the lift of the discharge lamp L can be extended effectively. |
