Research On The System And Stability For Cascaded Laser Drive Power

With the rapid development of laser technology in recent years,high-power semiconductor lasers have been widely used in the medical,communications and military fields.A laser is a semiconductor device that uses current injection as an excitation method.Its operating characteristics and lifespan largely depend on the performance of driving power supply.Therefore,it is of great significance to design a constant current source suitable for high-power lasers with stable,reliable and highperformance output.In this paper,a cascaded high-stabilization and low-ripple output laser driver was designed for the laser's volt-ampere characteristics.The main content of this article is as follows:(1)With the analysis of semiconductor lasers' volt-ampere characteristics and the stringent requirements on the driving power supply about electrical isolation,current ripple etc,this paper adopted an isolated cascaded driving power supply structure,in which a two-transistor forward topology was used in the source converter,and a staggered parallel topology was used in the load converter.In order to effectively reduce the output current ripple,a new control method is proposed in this paper.To make sure the load converter's two duty cycles were always in the optimal work area of approximately 50% and the cascaded system was always maintained at the optimal state of the theoretical zero ripple output,the output voltage was sampled and its double value was used as the voltage closed-loop given value of the source converter.(2)The source-load converter's working modes were analyzed detailedly and the corresponding hardware circuit was also designed.Meanwhile,the source load converter's small signal model in CCM mode and the closed-loop related transfer function were deduced.The Middlebrook stability criteria were also introduced to analyze the cascade system's stability.(3)This paper completed the source-load converter's closed-loop design by analyzing the cascaded converters' closed-loop impedance,discussing the relationship between loop gain and port impedance,comparing the effect of type II and type III compensators on closed-loop impedance,and analyzing the effect of load characteristics on stability.(4)Under the closed-loop control of the source-converter open-loop control of source-load converter,the influencing factors of the cascade-connected converter's port-impedance were discussed.Meanwhile,based on the cascade power supply system's experimental platform,the relevant experimental waveforms were collected.The theoretical analyses' reliability is verified,and the requirements for the laser's characteristics for high-performance power features are fulfilled.