Piezoelectric transformer driving curcuit and method capable of

Abstract

In a piezoelectric transformer driving circuit which comprises a boosting circuit (2) for boosting an input direct current voltage, a piezoelectric transformer (3), a current voltage converting circuit for converting a load alternating current which flows in the load (9), and a rectifier circuit (5), an input voltage detecting and comparing circuit (10) compares the input direct current voltage with a minimum voltage which is determined by a setting value of the load alternating current to produce a first voltage having a high level when the input direct current voltage is lower than the minimum voltage and to produce a second voltage having a low level when the input direct current voltage is higher than the minimum voltage. A reference voltage producing circuit (6a) produces one of first and second reference voltages in response to one of the first and second voltages. A main voltage comparing circuit (7) compares a rectified direct current voltage from the rectifier circuit with one of the first and second reference voltages to produce one of primary and secondary voltages. A frequency scanning oscillator (8) determines, in response to one of the primary and secondary voltages, a scanning direction of a driving frequency of a driving pulse signal which is supplied to the boosting circuit to supply the driving pulse signal to the boosting circuit. The input voltage detecting and comparing circuit may supply the first and second voltages to the current voltage converting circuit instead of the reference voltage producing circuit. In this event, the reference voltage producing circuit produces and supplies a reference voltage to the main voltage comparing circuit.