| 摘要 |
PROBLEM TO BE SOLVED: To control the output voltage of a piezoelectric transformer constant by converting an input voltage to a rectangular wave by alternately switching it with two switches and changing the energy of a fundamental wave constituent for adjusting the time ratio of the rectangular wave according to the input voltage. SOLUTION: A DC input voltage from a power supply 1 is converted to a rectangular wave Vds by a switching circuit 2 consisting of such switches as two MOSFETs and a rectangular wave Vds is converted to a sinusoidal wave V1 by a filter circuit 3. The sinusoidal wave V1 is inputted to a piezoelectric transformer 4 for converting a voltage by generating mechanical vibration, where the voltage is boosted to a sinusoidal wave V2 according to the input voltage and is outputted to a load cold cathode tube 5. Since the cold cathode tube is generally controlled by tube current, the tube current is detected by a detection circuit 6 and frequency is modulated by a V-f conversion circuit 7 so that a specific tube current is reached. A drive circuit 8 drives the switching circuit 2 in synchronization with the output from the V-f conversion circuit 7. |
