Method of driving a piezoelectric transformer and power source apparatus using the same

A power source apparatus comprising:

• a piezoelectric transformer with a primary electrode and a second electrode for stepping up a voltage input at the primary electrode by the piezoelectric effect to output the stepped up voltage from the secondary electrode;
• a driving section for driving the piezoelectric transformer at a desired voltage and at a desired frequency;
• a current detecting section for measuring a current across a load which is driven by the voltage output from the secondary electrode of the piezoelectric transformer;
• a step-up ratio differential detecting section for determining a linear differential value of the step-up ratio of the piezoelectric transformer with respect to the frequency;
• and
• a control section for controlling the driving frequency and the driving voltage for the piezoelectric transformer according to the current across the load detected by the current detecting section and the linear differential value determined by the step-up ratio differential detecting section.

A power source apparatus comprising:

• a piezoelectric transformer with a primary electrode, a secondary electrode and a third electrode for stepping up a voltage input at the primary electrode by the piezoelectric effect to output the stepped up voltage from the secondary electrode and the third electrode;
• a driving section for driving the piezoelectric transformer at a desired voltage and at a desired level frequency;
• a current detecting section for detecting a current across a load which is driven by the voltage output from the secondary electrode of the piezoelectric transformer;
• a step-up ratio differential detecting section for determining a linear differential value of a voltage ratio between the driving voltage for the piezoelectric transformer and the voltage output from the third electrode, to the frequency;
• and
• a control section for controlling the driving frequency and the driving voltage for the piezoelectric transformer based on the current detected by the current detecting section and the linear differential value of the step-up ratio determined by the step-up ratio detecting section so that the current across the load is at a predetermined level.