| 摘要 |
PURPOSE:To set and hold the driving voltage of a projection element at an accurate value by stopping the driving voltage variation of a driving voltage control circuit which varies a projection level in synchronism with the extinction of blink measurement light. CONSTITUTION:A turn-on synchronizing signal iRON and a bias signal BiAS synchronizing with said signal are outputted through an oscillation circuit, binary counter, RS type FF, logical gate, etc., and the turning-on operation of an analog switch 22 is controlled with the signal BiAS to charge a capacitor 28 gradually. When the switch 22 is off, on the other hand, the capacitor 28 is not charged and its charging voltage is held. Therefore, when the projecting element 31 is in a blink state with the signal iRON, i.e. in an off state, the capacitor 28 is not charged and the driving voltage of the element 31 has no variation. Then, the driving voltage of the element 31 rises stepwise through the signal BiAS whose output is stopped when the level attains to a specific level, and then held at the accurate value without exceeding the specific value. |
