Piezoelectric transformer drive circuit

Abstract

In a piezoelectric transformer drive circuit, a first autotransformer and a second autotransformer input to their primary terminals from a drive voltage control circuit and impress an ac voltage to each primary electrode of the piezoelectric transformer that is connected to each secondary terminal of the autotransformers; and the piezoelectric transformer supplies voltage generated from the secondary electrodes to a load. A frequency divider circuit alternately drives the first and second switching transistors connected to intermediate terminals of the first and second autotransformers. An output voltage comparison circuit compares the output voltage of the piezoelectric transformer with a prescribed maximum value, and if an overvoltage is detected in the output, the output voltage comparison circuit both outputs a reset signal to frequency control circuit and outputs a control signal to a dimmer circuit that changes duty ratio. The dimmer circuit generates a drive halt signal to drive voltage control circuit, performs duty ratio control, and outputs a control signal to the frequency control circuit such that the frequency of a VCO of the frequency control circuit does not change during drive halts. The frequency control circuit outputs a triangular wave signal to the frequency divider circuit, and the drive voltage control circuit inputs the power source voltage and controls the peak voltage driving the piezoelectric transformer to a fixed level. Furthermore, coils may be used in place of autotransformers.