VOLTAGE CONVERSION DEVICE USING PIEZOELECTRIC TRANSFORMER

PURPOSE: To improve the efficiency of a voltage conversion device, and stabilize the same by providing a temperature compensation means, and detecting the ambient temperature of a cold cathode tube so as to temperature-compensate the power adjustment circuit portion of a power variable type amplification circuit. CONSTITUTION: The power adjustment circuit portion of a power variable type amplification circuit 12 is equipped with a dimming oscillation circuit 20 and a drive circuit 25, and power variability is adjusted by the duty ratio of an intermittent drive. A temperature compensation element 19 detecting the ambient temperature of a cold cathode tube 17 is inserted in series into an outside fitting variable resistor 15 in the circuit 20. In the output of the circuit 20 the operation time of the circuit 25 is adjusted corresponding to the ambient temperature of the cold cathode tube 17 by the temperature compensation elements 19, 19' so that the brightness of the cold cathode tube 17 is made constant soon after power supply closing. Since the elements 19, 19' have negative characteristics, a resistance value becomes large when the ambience temperature is decreased and the resistance value becomes small when the ambience temperature is increased. Thereby, when the operation time of the circuit 20 is lengthened or shortened corresponding to the ambient temperature, an input voltage to a piezoelectric transformer 16 becomes large or small so that the brightness of the cold cathode tube 17 is made constant.