| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide an operation panel having a display panel, and extend the lifetime of a lamp used as a back light. SOLUTION: A current-carrying amount computation part 33 is started based on notification that a fluorescent tube 17 should be turned on from a lighting command part 27, and integrated value data of current-carrying time is read from a lighting time integration part 23 to determine cumulative operating time of the fluorescent tube 17. Then, the current-carrying amount data is read from a phase information storage part 31 to determine the current-carrying amount corresponding to the cumulative operating time of the fluorescent tube 17, and the determined current-carrying amount is supplied to a phase control part 35. The current-carrying amount computation part 33 compares a brightness value, detected by a brightness detection part 25, of the fluorescent tube 17 to brightness value data for the purpose of confirming that the brightness of the fluorescent tube 17 is controlled to a predetermined brightness value through the phase control part 35 and a semiconductor control rectification circuit 19. The phase control part 35 outputs a control signal to a gate circuit of the semiconductor control rectification circuit 19 on the basis of the current-carrying amount data from the current-carrying amount computation part 33, thereby controlling the output timing of gate pulses impressed on a gate terminal of two thyristors in the circuit 19.</p> |
