Patent ID: 6737816
Filing Date: 2004-05-18
Classification: H01L,H05B

Abstract:
A piezoelectric transformer drive circuit comprising:a piezoelectric transformer for outputting a voltage input to a primary terminal from a secondary terminal by virtue of a piezoelectric effect, said piezoelectric transformer having a sensor electrode for detecting a voltage lower than the output voltage from said secondary terminal, a drive circuit for driving said piezoelectric transformer, a variable oscillation circuit for supplying a desired frequency and a desired voltage from said drive circuit to said piezoelectric transformer, a discharge tube, the input terminal of which receives the output voltage of said piezoelectric transformer and the output terminal of which is connected to a feedback resistor, an overvoltage protection circuit for detecting the output voltage from said sensor electrode, for comparing said output voltage with a first reference voltage and for outputting the result of the comparison, comparison means for comparing the voltage value of said feedback resistor with a second reference voltage so that the current flowing through said discharge tube becomes constant and for outputting the result of the comparison, a frequency control circuit for controlling the drive frequency of said piezoelectric transformer on the basis of the result of the comparison from said overvoltage protection circuit before the lighting start of said discharge tube and for controlling the drive frequency of said piezoelectric transformer on the basis of the result of the comparison from said comparison means while said discharge tube is lit.