Piezoelectric-transformer inverter

A piezoelectric-transformer inverter comprising:

• a piezoelectric transformer operating to transform an AC voltage applied between its primary electrodes to a transformed voltage supplied to a load connected to its secondary electrode, said piezoelectric transformer comprising:
• a piezoelectric substrate having a first region which is polarized in a first direction and a second region which is polarized in a second direction different than said first direction;
• a plurality of electrode films layered in said first region and connected together into first and second groups to form said first and second primary electrodes;
• and
• an electrode formed on an end surface of said piezoelectric substrate located substantially adjacent said second region to form said secondary electrode;
• a first coil and a first switching element connected to said first primary electrode of said piezoelectric transformer;
• a second coil and a second switching element connected to said second primary electrode of said piezoelectric transformer;
• a drive circuit which alternately drives said first and second switching elements such that the phase of the voltage applied between said primary electrodes is reversed cyclically;
• and
• drive frequency control circuit which controls an AC current flowing through said load at a predetermined value by changing the operation frequency of said drive circuit;
• said piezoelectric transformer operating in a half wavelength mode.