| 摘要 |
PURPOSE:To prevent overcurrents, and to obviate a breakdown by overcurrents of a semiconductor laser by connecting a Zener diode between a control terminal and an output terminal for a constant-current circuit. CONSTITUTION:A DC bias circuit 5 is formed in constitution in which a Zener diode 53 is connected between a base of a transistor 51 constituting a constant- current circuit and negative power supply voltage and a control signal (a) from a comparison circuit 3 is inputted to the base of the transistor 51 through an operational amplifier 52. Since the Zener diode 53 protects so that the base voltage of the transistor 51 does not reach a fixed value or more at that time, high currents do not flow through a semiconductor laser 1 even when a large signal is applied to the DC bias circuit 5 due to a short circuit, etc., and the breakdown of an element can be prevented. The DC bias circuit is very effective when it is applied to an APC circuit. |
