Patent ID: 6229833
Filing Date: 2001-05-08
Classification: H01S

Abstract:
A laser driving current control circuit in which a laser diode of common-anode type or common-cathode type, a semiconductor switch and a resistor are connected in series, and feedback control is performed in such a manner that terminal voltage produced across the resistor by a laser driving current will become equal to a set voltage, whereby the laser driving current is made to attain a set value, comprising:a first emitter follower circuit in which semiconductor elements having different polarities are connected complementarily, an emitter follower is constructed regardless of which semiconductor element turns on, and the set voltage is input thereto;a second emitter follower circuit in which semiconductor elements having different polarities are connected complementarily, an emitter follower is constructed regardless of which semiconductor element turns on, and a feedback voltage conforming to the terminal voltage is input thereto;an attenuator for attenuating output voltages of the first and second emitter follower circuits;an operational amplifier in which the set voltage and the feedback voltage, which have been attenuated by said attenuator, are input to an inverting input terminal and a non-inverting input terminal, respectively, for outputting a signal which turns the semiconductor switch on/off based upon the sizes of both voltage signals; anda third emitter follower circuit in which semiconductor elements having different polarities are connected complementarily, an emitter follower is constructed regardless of which semiconductor element turns on, and the output signal of the operational amplifier is input thereto;said semiconductor switch being turned on/off by the output signal of said third emitter follower circuit.