| 摘要 |
PURPOSE:To control a maximum current in accordance with an ambient temperature by a method wherein a thermistat is inserted between the collector of a 1st transistor constituting a voltage-current converting circuit and the base of a 2nd transistor constituting a current mirror circuit. CONSTITUTION:When an input voltage V is applied to an input termind 1, a current i1 which is increased proportionally to the input voltage is applied to the collector of a 1st transistor Q1. When the transistor Q1 is saturated, the current i1 reaches the maximum input current and the current increase is stopped. The maximum current is varied in accordance with the resistance of a thermistor TH which is varied by an ambient temperature. On the other hand, as the output current i2 of a 2nd transistor Q2 is proportional to the output current i1, it is also influenced by the thermistor TH. The resistance of the thermistor shows negative characteristics against the ambient temperature, the higher the temperature, the larger the maximum current. With this constitution, the maximum current for driving a semiconductor laser 4 can be satisfactorily predetermined in accordance with the ambient temperature. |
