| 摘要 |
PROBLEM TO BE SOLVED: To cope with significant variation in supply voltage or load on a piezoelectric transformer and thus improve driving efficiency by controlling a pulse width varying means so that, if the difference between a resonance frequency and the frequency of a precursor signal falls within a preset range, the current passed through the load will be made constant. SOLUTION: A feedback resistance 6 having a small value is connected in series with a cold cathode fluorescent lamp 5, and the current passed through the cold cathode fluorescent lamp 5 is detected through the feedback resistance 6. The voltage across both the ends of the feedback resistance 6 is input to a current detect circuit 7. The current detect circuit 7 detects a current passed through the cold cathode fluorescent lamp 5 from the voltage across both the ends of the feedback resistance 6, and inputs the result of the detection to a pulse width control circuit 9. The pulse width control circuit 9 controls the pulse width of output signals from a variable oscillation circuit 1 by means of a pulse varying circuit 10 so that the voltage across both the ends of the feedback resistance 6 will become constant, in other word, a load current passed through the cold cathode fluorescent lamp 5 will become constant. This makes the current of the cold cathode fluorescent lamp 5 almost constant. |
