| 摘要 |
PROBLEM TO BE SOLVED: To suppress the generation of a high-frequency voltage at the start of a driving operation by a method wherein a driving signal is set at a specific frequency, the sweep of a driving frequency is stopped when a load current becomes a set value and the load current is controlled within a set frequency range having a definite relationship with a resonance frequency at the actual driving operation of a piezoelectric transformer. SOLUTION: A current detection circuit 7 detects an inflow current to a load (e.g. a cold- cathode fluorescent lamp) 5. At the start of a driving operation, a frequency control circuit 8 sets a driving signal to a high frequency which is within 1.1 times (preferably within 0.7 times) a resonance frequency at the actual driving operation of a piezoelectric transformer 4, it starts the sweep of a driving frequency by using the driving signal, stops the sweep of the driving signal when a load current by the current detection circuit 7 becomes a set value, and controls the load current within a set frequency range having a definite relationship with the resonance frequency at the actual driving operation of the piezoelectric transformer 4 after stop of the sweep. Thereby, it is possible to suppress the generation of a high-frequency voltage from being generated at the start of the driving operation of the piezoelectric transformer, and its driving efficiency can be increased. |
