The Key Technologies Of High-power Semiconductor Laser Drive Power Supply

As a driver and controller of high-power semiconductor laser, the high-powersemiconductor laser driver (laser driver for short) bear the important task of drive, control andprotection of high-power semiconductor laser, the merits of its technical performance closelyrelated to the reliability and service life of high-power semiconductor laser system. There areseveral key techniques to determine the performance of laser driver, such as soft-start, fastover-current protection, constant current output control, master-slave control. According totechnical requirements of high power semiconductor laser used in industry, the above keytechniques have been researched in this paper, both theoretical and experimental.For researching key techniques of laser driver, it is necessary to build an equivalentcircuit model of high-power semiconductor laser. However, due to lacks of parasiticparameters, the existing circuit model of LD (laser diode) is insufficient of simulatinghigh-power semiconductor laser. An equivalent circuit model has been built which includeparasitic inductance and parasitic capacitance, based on rate equation of laser diode.Simulation and test results show that the V-I curve and P-I curve of the equivalent circuitmodel are consistent with the manufacturers, so it can be used as the equivalent load of laserdriver.Soft-start is a function required for a laser driver, the traditional soft start methods whichstarting current are non-linear growth lead to a large error between the actual start time andthe setting. When several laser drivers power on simultaneously, their output current increasenon-synchronously. For this reason, a linear soft-start technique was introduced which based on a way ofconstant current charge, by charging the capacitor with constant current source, the capacitorvoltage increases linearly, therefore the error of soft start time reduce obviously.At present, when output current of laser driver change suddenly, most of the laser driverwas cut off by software according over-current signal. Due to software filter need some time,the response time of over current protection was too long. This paper proposes a fast overcurrent protection circuit, which mainly consists of a fast shutdown and self-locking circuit.When the laser driver output current excess setting, a high-speed comparator will detect theover current signal, a JR trigger will then hold the protection action, while another fast cutoffcircuit shut the laser driver down. The whole series of protection actions could be finishedwithin in20microseconds.In order to verify the performance of the fast over-current protection circuit, threeover-current conditions, such as power on overshoot, electromagnetic interference and loadchange suddenly, have been simulated. Test results show the fast over-current protectioncircuit work well under all over-current conditions.PID （Proportion Integration Differentiation）feedback control technique is often used inlow power laser driver, it can get good output performance, but low power convert efficiency,while PWM（Pulse Width Modulation）feedback control technique is often used in high-powerlaser driver, it can obtain high convert efficiency, but poor output performance. Integratingthe advantages of both, a dual loop control techniques has been designed based on PID+PWMfeedback control, by which the output voltage of laser driver was controlled by PWM loopand output current of laser driver was controlled by PID loop, so it can get not only goodoutput performance but also high convert efficiency.Using linear soft-start technique, fast over-current protect technique and dual loopconstant current output control based on PID+PWM, five high-power semiconductor laserdrivers, each output power10kW, have been developed. The laser driver has a master-slave function, so output of the slave can follow the master, and each laser driver can be set asmaster or slave.Tests show that output current of the designed laser driver increases linearly when itpower on, soft start time can be controlled accurately and the error is less than1millisecond.Laser driver can be cut off in20microseconds when over current occur. Furthermore itsoutput current ripple is less than1%, and output stability is less than0.04%, and the convertefficiency can reach87%. Five laser drivers can be combined into a master-slave system,which can drive five high-power semiconductor lasers work synchronously.