| 摘要 |
PURPOSE:To limit the duration of the emission of a semiconductor laser upon the input of a signal sustained for an abnormally long time by a method wherein the inputted signal is supplied to both delay circuit and differentiating circuit. CONSTITUTION:A signal A to be applied to an input terminal 1 is kept at a high level when the input signal line is out of connection or when the input signal line experiences such abnormalities as accidental disconnection. A signal B is obtained by differentiating the signal A fed from the input terminal 1 in a differentiating circuit 3. The signal B is obtained by discriminating a signal C in a comparator 5. Differential signals E and F are the logical products of the signals C and D. The signal F is inputted into the base of a transistor 8 for the generation of a current G to drive a semiconductor layser 9. The semiconductor layser 9 emits only for a period subject to a time constant present in the differentiating circuit 3 as indicated by a current waveform G even when the signal A is kept at a high level. |
