| 摘要 |
PROBLEM TO BE SOLVED: To impart sufficient electric power to a lamp, and improve starting performance by a simple circuit by setting a controlled variable to control switching elements of a control means for a prescribed period in the almost same as a controlled variable at no-load condition time. SOLUTION: A delay circuit 7 outputs a signal by delaying it for about several seconds when a signal from a lighting discriminating circuit 6 changes to a high level from a low level. A frequency changeover switch 10 inputs the signal of the delay circuit 7 to a low frequency drive circuit 11 by connecting to an oscillator 8 at low level time in a no-load condition, and to an oscillator 9 at high level time in a lighting condition. The low frequency drive circuit 11 divides signals of the oscillators 8 and 9, and generates and outputs a signal to turn on and off switching elements Q1 to Q4 in an inversion circuit part. Therefore, a frequency of a rectangular wave is maintained in a value at no-load time for several seconds just after discharge condition unstable lighting is started, and extinction of a lamp is prevented, and starting performance is improved. |
