Patent ID: 6911787

Claim:
A method for driving a piezoelectric transformer in which a primary side electrode and a secondary side electrode are formed in a piezoelectric body, and a driving signal input from the primary side electrode is converted and output from the secondary side electrode to a load, comprising the steps of: detecting an output state to the load to generate a detection signal; and generating the driving signal for controlling a driving frequency and input power of the piezoelectric transformer based on the detection signal, wherein the driving signal is a signal in a rectangular waveform having time periods up to an n-th (n is a natural number of 1 or more) time period in which a level is varied successively from a maximum potential and a minimum potential to an intermediate potential, obtained by respectively multiplying a period of the driving signal by time ratios up to an n-th time ratio, a sum of the time ratios up to the n-th time ratio is set to be smaller than 0.5, and the time ratios up to the n-th time ratio are set so as to minimize a sum of ratios of values of respective higher order input currents with respect to a value of an input current with a frequency that excites the piezoelectric transformer.