| 摘要 |
PROBLEM TO BE SOLVED: To light up a lamp in a stabilized manner even if a current limiting element is made small by directly controlling a lamp current itself by superposing a direct current voltage on an alternating current voltage. SOLUTION: When switching elements S1, S4, and S2, S3 are alternately turned on and off with the same on-duty, an oscillation circuit works to apply since wave alternating voltages to a lamp LP. If the on-duty of the elements S1, S4 is elongated and that of the elements S2, S3 is accordingly shortened, a DC voltage Vdc is superposed on the lamp LP. When the DC voltage V dc is superposed on the amplitude of a basic resonance voltage Vac and the peak is Vac+Vdc, it exceeds a characteristic voltage V1a. Even of the pekl is Vac- Vdc, a state is realized in which the peak is lower than V1a. In this way, the on-duty ratios of the element S1, S4 and S2, S3 are controlled to alternately apply voltage higher and lower than the lamp characteristic voltage V1a, so that the lamp may be lit up with stability even if a current limiting element is made smaller. |
