| 摘要 |
PROBLEM TO BE SOLVED: To achieve improvement of power converting efficiency and decrease of loss of a piezoelectric transformer by making a constant amplitude of the input voltage of a piezoelectric transformer by a Dc /Dc converter, and taking the tube current error into the Dc /Dc converter and a driving circuit. SOLUTION: The voltage Dc of an input power source is supplied as a sine wave to a piezoelectric transformer 2 through a driving circuit 1, the high voltage is applied to a cold-cathode tube FL, and the tube is lighted up. In a cold-cathode tube driving device 10, the input voltage Dc is supplied to the driving circuit 1 after being stabilized to the constant voltage by a Dc /Dc converter 7. The tube current I is detected by a tube current detecting circuit 3. The detected and output a.c. voltage is rectified by a rectifying circuit 4 and supplied to an error amplifying circuit 5. The differential voltage between the output voltage V4 of the rectifying circuit 4 and the reference voltage Vref is amplified. This output voltage V5 is converted into a frequency signal by a V/F converting circuit 6 and transmitted to the Dc /Dc converter 7 and the driving circuit 1. The switching frequency and the driving frequency are equalized to each other, and the transmitting frequency and the resonance frequency of the piezoelectric transformer are also equalized to each other. |
