| 摘要 |
<p>PURPOSE:To gradually darken a discharge lamp when a power source switch is OFF by varying the ON-duty or switching frequency of the switching element of an inverter circuit within a fixed time from the OFF-time of the power source switch. CONSTITUTION:When a power source switch S is ON, now, a capacitor C3 is charged to a fixed voltage determined by the divided voltage of resistors R1-R3 since a switch element Qx is OFF, and the duty of the output fH of a comparator CP1 in this case is constant. When the switch S is OFF, the electric charge of the capacitor C3 is discharged through the resistor R2, the element Qx, and the resistor R3, and voltage Vx across the capacitor C3 is gradually reduced. Thus, the ON-duty of a rectangular wave signal fH as the output of the comparator CP1 is gradually reduced in accordance with the reduction of the voltage Vx. Thus, the ON-period of the switching element of an inverter circuit is also shortened, and a discharge lamp is gradually darkened.</p> |
