| 摘要 |
<p>PURPOSE: To reduce the flicker and cyclic light and darkness owing to the change of light flux by making the voltage of a capacitor be an output signal, and off-controlling a switch when an illuminance detection signal stays between predetermined reference signal levels. CONSTITUTION: A comparator 13 compares the output signal voltage V1 of an illuminance detection circuit 11 with the output signal voltage V2 of an illuminance setting circuit 12, and outputs a low or high level signal voltage V3 to a time constant circuit 14 depending on whether the voltage V1 exceeds the voltage V2 or not. In the circuit 14 when the voltage V3 is at a high level, the voltage of a capacitor C1 rises according to a predetermined time function, and when the voltage V3 is at a low level, the voltage V4 falls according to a predetermined time function. When the signal V1 stays between first reference signal level V6 and second reference signal level V7 , a control signal generating circuit sends the output signal of the voltage V4 of the capacitor C1 to a comparator 18 so as to off-control a switch SW. The switch SW is turned off so that the voltage V4 is maintained until V1 >V6 is met, and thereafter, the switch SW is turned on.</p> |
