COLD CATHODE TUBE LIGHTING DEVICE

摘要

PROBLEM TO BE SOLVED: To prevent a cold cathode tube from being put in a lighting impossible state by operating a protective function of an inverter by a dark effect of the cold cathode tube. SOLUTION: An inverter circuit 21 contains an inverter main circuit 31 for generating voltage required to light a cold cathode tube 26 and a protective circuit 32. When the cold cathode tube 26 delays in lighting by a dark effect, the protective circuit 32 cuts off input of a power source by judging it as an opening state. A cutoff of the power source is detected by an electric current detecting amplifier 29 as a change in end-to-end voltage of an electric current detecting resistance 24. A microcomputer 30 repeatedly controls stopping and a restart of operation of the inverter circuit 21 through an FET 28 to continue operation of the inverter circuit 21 as it is when a lighting current corresponding to lighting of the cold cathode tube 26 is detected in a range of a repetitive condition decided in response to the dark effect.