Patent ID: 6407480
Filing Date: 2002-06-18
Classification: H05B

Abstract:
A piezoelectric transformer-driving circuit comprising:a piezoelectric transformer which is supplied with a controlled current to be supplied to a cold cathode tube and driven at the frequency of a drive pulse signal, a current detector for detecting a load current flowing through said cold cathode tube, a rectifying circuit for converting a sine wave like AC voltage obtained from said current detector into a substantially DC voltage, an A/D converter for converting the voltage signal rectified by said rectifying circuit into a digital signal, an error voltage calculation circuit for multiplying the difference data between the output data of said A/D converter and reference data supplied externally by a constant and for outputting the result as error data, a frequency setting circuit for setting the frequency of said drive pulse signal of said piezoelectric transformer as M-bit data (M: an integer) depending on said error data, a divider circuit for dividing a clock having a predetermined frequency at a predetermined frequency division ratio to generate said drive pulse signal of said piezoelectric transformer, for distributing said frequency division ratio for the period of N cycles (N: an integer) of said drive pulse signal of said piezoelectric transformer and for carrying out control so that the average frequency division ratio for said period of N cycles is substantially equal to the value obtained by dividing said M-bit data output from said frequency setting circuit by N, and a power transistor for driving said piezoelectric transformer.