| 摘要 |
PROBLEM TO BE SOLVED: To provide a voltage resonance type power supply improving its enlargement and high cost without using a transistor having a high withstand voltage to cope with an increase of the peak value of the resonance voltage as a switching transistor on the primary side. SOLUTION: After the fluorescent lamp lighting signal ST is detected (S11), the resonance voltage on the primary side is detected by a resonance voltage detecting circuit. The off-time Toff of a PWM1 is measured by a PWM1 off- time measuring circuit based on the detected value. When the off-time Toff becomes the prescribed value Toff1 or above (S12), the setting of the on-time Ton of the PWM1 is fixed and controlled to the prescribed value Ton1 by a PWM1 latch circuit (S13). The latch state is maintained until the off-time Toff of the PWM1 becomes the Toff1 or below. When the off-time Toff of the PWM1 becomes Toff1 or below (S14), the latch state of the PWM1 is released, and the normal control is resumed (S15). |
