| 摘要 |
PURPOSE:To avoid a breakdown of a laser diode caused by an overcurrent by a method wherein the current of the laser diode is observed and when the current is going to exceed a specified value, the impedance of the circuit connected to the laser diode in parallel is reduced, so that the surge current is by-passed. CONSTITUTION:A transistor TR17 is connected to a circuit of a laser diode 2 in parallel and the emitter circuit of the TR17 is connected to a resistor 19. When a current begins to flow through the diode 2 by some reason, a voltage is produced between the both ends of an emitter resistor 13 of a compound TR3 by the surge current and the voltage is applied to the TR17 through a base resistor 18. If the circuit is so designed that a base voltage produced by the surge current is saturate enough by the TR17, most of the surge current will flow through the TR17. With the above method the diode 2 is protected from deterioration or breakdown caused by the surge current. |
