The Design And Manufacture Of General Semiconductor Laser Diode Driver

In recent years, the application of the semiconductor laser diode isbecoming more and more widespread in the military and civilian field. It hasfurther brought into focus the driver that applied with the laser diode ingeneral. So it is necessary to develop the laser diode driver of high quality.Because the laser diode itself asks for very harsh work condition, the laserdiode driver should be stable and reliable, can make the laser diode worksafely, have a strong anti interference ability and ensure a normal useful life ofthe laser diode.However, the rapid development of modern electronic informationtechnology puts forward a more and more high request for a kind of smaller,portable, multifunctional, highly reliable and low cost laser diode driver. Thispaper has made renovation and upgrade by further exploration on the basis ofthe original laser diode driver product JD2500, which removed the redundantparts and replaced the primary components by SMD. It comes to meet thedesign request and perform all the function of the control modules. Some of itstechnical indicators have reached the level of similar products at home andabroad. The short term stability of the output current is 21ppm, and itslong term stability is 37ppm. Furthermore, this driver is smaller in size andmore convenient to operate.The driver can provide three kinds of drive mode: constant current drive,constant power drive and pulse drive. Also, as for security of an operatinglaser diode, it takes necessary protective measures as follow: 1.soft start anddelaying circuit avoids the laser diode being frustrated by the impulse during the power on; 2. The independent set of the limit current ensure the laser diodeof safe current; 3.the relay circuit prevents the impulse raised by turning on thepower.All of these protective measures have made the laser diode work safely.Based on the principle of current series negative feedback, the drivingmodule realizes closed loop control of control parameters and enhances thestability of the driver system. According to different feedback parameter, thedriving module is divided into constant current control and constant powercontrol, which are respectively fit for stabilizing the afflux current and theoutput light power. In this driver,we use external signal to provide the pulsecurrent.The constant current drive circuit is mainly composed of voltagebenchmark circuit, voltage current conversion circuit, modulation input circuitand protection circuit. The whole design idea is to use the principle of negativefeedback to stabilize output current, which obtains the lowest current error andthe highest current stability.Consider the design of the constant power control module. When thesemiconductor laser diode operates in a long period, the output light powerwill be variable owing to many kinds of reasons, but we hope that the laserdiode can maintain relatively constant light power. Therefore, laser diode isnecessary to work in the mode of constant power. The principle of constantpower drive is: PD converts the change of output light power of laser diodeinto the change of diode current, and the change of current is feed back tovoltage current converser which adjusts output current of driver to compensatethe laser diode. So, when output light power attenuates, driver will increaseoutput current accordingly; when output light power increases, driver will reduce output current accordingly.For the applications of laser diode, pulse output is preferable, becausepulse output has very low junction heat. In this driver, we use external signalto provide the pulse current, and the external signal is introduced from theterminal of modulation input. So the frequency of pulse drive mode amountsto the frequency of external signal, and the operate frequency of driver shouldbe below the frequency of MOSFET.After theoretically analyzing the main factors that have an effect on thestability of the driver system, this paper takes relevant actions to guarantee thestability of the driver system and develops a prototype of the driver on thebasis of considering the electromagnetic compatibility. In the light ofevaluation by a corresponding experiment, the parameters of the driver aresatisfied with the design request.