Drive circuit for driving a piezoelectric transformer capable of

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. The switching signal may be supplied to the drive voltage control circuit to make the drive voltage control circuit decrease the input power of the input DC voltage.