| 摘要 |
PURPOSE:To prevent a light emitting element from being destroyed with an excessive current, by driving the light emitting element through the control of discharge energy of a capacitor once charged. CONSTITUTION:A switching circuit 42 has an oscillation circuit. A capacitor 40 is charged at the first ''H'' level of the oscillation output and the charge in the capacitor 40 at the next ''H'' level is applied to a capacitor 41. When a terminal voltage of the capacitor 41 reaches a power supply voltage with some cycles of the oscillation output, an MOS transistor 36 is conductive and a charge in the capacitor 41 is applied to a light projecting and photodetector 11 for light emission. Since the amount of electricity charageable in the capacitor 41 is very little, the element can not be destroyed. |
