Piezoelectric transformer inverter

摘要

A piezoelectric transformer inverter includes an inverter unit and a step-down chopper unit. The inverter unit includes a ceramic piezoelectric transformer whose secondary terminal is to be connected to a fluorescent tube, a drive unit which is connected to a primary terminal of the ceramic piezoelectric transformer, and an inverter control circuit for controlling luminance of the fluorescent tube to a desired value. The step-down chopper unit includes a switching device which is disposed on the side where the voltage of the inverter unit is input, a free wheeling device connected between the switching device and a reference potential, and a PWM feedback control circuit for providing a feedback control to maintain an average voltage of the rectangular-wave voltage of the switching device constant. In the piezoelectric transformer inverter, even when the feedback control by the PWM feedback control circuit is impossible, the on-duty of the chopper unit is restricted so that it is not greater than a given amount.