| 摘要 |
PURPOSE:To obtain a semiconductor laser drive circuit excellent in safety by a method wherein at least two or more forced quenching circuits independent of each other are provided. CONSTITUTION:A semiconductor laser drive circuit is composed of a current feed circuit which supplies a drive current to a laser diode 1a responding to a lighting signal LDON to start it emitting light, a first forced quenching circuit which stops feeding a drive current to the laser diode 1a to forcedly turn off it responding to a forced stop signal LDINH 1, and a second forced stop circuit which responds to a forced stop signal LDINH 2. When an emergency occurs, the forced stop signal LDINH 1 is made to turn high in level, a transistor 12 becomes non-conductive, the second forced stop signal LDINH 2 is made to turn low in level, a transistor 15 becomes conductive, a voltage between the anode and the cathode of the laser diode 1a becomes smaller than a forward voltage, a current fed from a power supply line Vcc is made to flow through a transistor 15 bypassing the laser diode 1a, so that the laser diode 1a is forcedly turned OFF. |
