A piezoelectric transformer control method of generating an oscillation signal in accordance with a control voltage, driving a piezoelectric transformer by an AC voltage generated in accordance with the oscillation signal, detecting a load current of a load connected to an output side of said piezoelectric transformer, and controlling an oscillation frequency so as to keep the load current substantially constant, comprising the steps of:
- detecting an output voltage from said piezoelectric transformer;
- detecting an open state and short-circuiting to ground on the output side of said piezoelectric transformer based upon comparing the detected output voltage with first and second predetermined values;
- and
- controlling the oscillation signal in response to the comparison.