| 摘要 |
PURPOSE:To prevent neglection in turning-off of a power supply switch by disposing a photodetector to detect the brightness in a room on the outside surface of a body and providing means of turning off the power supply switch when the brightness detected by the photodetector is below a specified level. CONSTITUTION:A voltage at the point B divided down by resistors 3, 4 is inputted to a + input terminal of a comparator 5. This voltage Vb is a reference level to decide the off of a main relay 10. The voltage at the point A divided down by the photodetector 1 and the resistor 2 is inputted to a - input terminal of the comparator 5. The resistance value of the photodetector 1 increases when it becomes dark in the room and, therefore, the partial voltage at the point A increases and the output of the comparator 5 falls to an L level, thus turning off a transistor 9. Therefore, even if a user retreats from the room while neglecting to switching off of the power supply switch 12 of a copying machine in the night time, the transistor 9 is turned off by darkening of the room inside when the operator turns off the power supply for illumination at the time of the retreat. The main relay 10 is then turned off and respective contacts 10a-10d are opened to stop the current supply to loads 26, 27. |
