| 摘要 |
PROBLEM TO BE SOLVED: To provide a low cost high voltage power supply with which a surge current is not produced at the time of ON/OFF of a switching device and which has a high reliability and produces little noise. SOLUTION: The one side ends of choke coils 1 and 3 are connected to the anodes of diodes 11 and 12. The cathodes of the diodes 11 and 12 are connected to the drains of FET's 2 and 4. The sources of the FET's 2 and 4 are grounded. Two such series circuits of the choke coils, diodes and FET's are provided in parallel with each other. A DC power supply 8 is connected to the connection point of both the other side ends of the choke coils 1 and 3. Further, the connection points A and B of the choke coils 1 and 3 and the diodes 11 and 12 are connected to the primary electrodes 5a and 5b of a piezoelectric transformer 5 respectively. A high voltage is outputted from the secondary electrode 5c of the piezoelectric transformer 5 and supplied to a load such as a cold cathode tube 6. Two driving signals whose phases are 180 deg. different from each other and whose duty ratios are 50% are applied to the gates of the two FET's 2 and 4. The constants are so determined as to have a resonance frequency which is determined by an equivalent capacitance between the primary electrodes of the piezoelectric transformer 5 and the inductances of the choke coils 1 and 3, the resonance frequency of the piezoelectric transformer 5 and the frequencies of the driving signals approximately equal to each other. |
