US Patent 7423362 Piezoelectric transformer drive method and drive circuit

A driving circuit is composed of a discontinuous rectangle wave oscillator and a lowpass filter. A discontinuous rectangle wave used herein is composed of voltages Vp, 0 and −Vp. Assuming one cycle is T, a discontinuous rectangle wave has such a configuration that a potential from a time 0 to a time ø is a potential 0, from the time ø to a time (T/6−ø) is a potential Vp, from the time (T/6−ø) to a time (T/3+ø) is a potential 0, . . . . Since the third harmonic wave is not included in the discontinuous waveform, the inductance of the lowpass filter can be reduced. Consequently, the lowpass filter may be omitted. Further, the amplitude of the fundamental wave can be changed by varying the phase difference ø.