Abstract: The present invention provides a driving circuit for a piezoelectric transformer. The driving circuit comprises a driver circuit and a detector circuit. The driver circuit is electrically connected to a primary side of the piezoelectric transformer for generating a driving signal which is transmitted to the primary side of the piezoelectric transformer so that the piezoelectric transformer exhibits a vibration due to piezoelectric effect and generates a transformed output voltage on a secondary side thereof. The detector circuit is electrically connected to an output side of the driver circuit for receipt of the driving signal from the driver circuit and also electrically connected to the secondary side of the piezoelectric transformer for receipt of the transformed output voltage from the piezoelectric transformer so that the detector circuit is capable of detecting a drop of the transformed output voltage when a voltage level of the driving signal is in an available range.

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.

Abstract: In a drive circuit for a piezoelectric transformer that comprises an inverter circuit for supplying first and second primary electrodes of a piezoelectric transformer with a main drive voltage, a frequency control circuit having a normal frequency sweeping range, and a drive voltage control circuit for controlling input power of an input DC voltage supplied to the inverter circuit, an overvoltage protection circuit detects overvoltage in an output AC voltage from the piezoelectric transformer. On detection of the overvoltage in the output AC voltage, the overvoltage protection circuit supplies the frequency control circuit with an additional reset signal and a switching signal, thereby making the frequency control circuit switch the normal frequency sweeping range to a provisional frequency sweeping range included in the normal frequency sweeping range.