CONTROL CIRCUIT OF PIEZOELECTRIC TRANSFORMER

摘要

PROBLEM TO BE SOLVED: To provide a control circuit of a piezoelectric transformer which can practice a stable step-up operation even if a waveform distortion is produced in an input voltage of a piezoelectric transformer by the adjustment of a duty ratio of an oscillation signal corresponding to a fluctuation of a DC power supply voltage. SOLUTION: In a control circuit which generates an AC high voltage for driving a cold cathode tube 2, a notch filter 9 whose central frequency is twice a drive frequency of a piezoelectric transformer 1 is inserted in a line for applying an input voltage Vi to the piezoelectric transformer 1, and a distortion having a frequency component with the twice frequency and superposed upon the input voltage is eliminated by the notch filter. The control circuit drives a Rosen type laminated piezoelectric transformer by a half-bridge type drive circuit 6 with a λ/2 mode.