Piezoelectric inverter

A piezoelectric inverter for driving a load using a piezoelectric transformer, comprising:

• input voltage control means, having a switching transistor and a current circulating element, for converting a direct-current input voltage into a rectangular alternating-current voltage;
• piezoelectric transformer drive means, connected between the input voltage control means and the piezoelectric transformer, and comprising an inductive element, for outputting, to the piezoelectric transformer, an alternating-current voltage having a substantially constant frequency that is lower than the frequency of an output alternlating-current voltage of the input voltage control means;
• a first oscillator for determining an operating frequency of the input voltage control means;
• a second oscillator for determining an operating frequency of the piezoelectric transformer drive means;
• the piezoelectric transformer having an input electrode and an output electrode with the input electrode thereof connected to the piezoelectric transformer drive means and the output electrode thereof connected to the load;
• load current detector means, connected to the load, for detecting a load current;
• and
• duty factor control means, connected to the load current detector means, for controlling a duty factor of a rectangular pulse of the input voltage control means in response to the output of the load current detector means so that the load current is maintained to a substantially constant target current value,
• wherein an oscillation frequency of the second oscillator is not higher than a frequency at which the voltage multiplication ratio of the piezoelectric transformer becomes maximized with no load applied to the output of the piezoelectric transformer, and the oscillation frequency of the second oscillator is not lower than a frequency at which the voltage multiplication ratio of the piezoelectric transformer becomes maximized with the piezoelectric transformer driving the load connected to the output thereof.