The Design For Semiconductor Laser Constant Source Signal Convert Circuit

With the rapid development of science and technology, the techniques of semiconductor laser diode had been applied widely in many fields such as industry, high tech and science research. Semiconductor laser diode has the excellent character of high efficiency, small size, low weight, high reliability, direct modulation ,but semiconductor laser diode is a kind of device with high power density and sky-high quantum efficiency. Even weak drive current and temperature change will lead to its large change of output light power and device parameters, which directly damages the safe use of laser diode, so higher request to the laser diode driver is put forward . The control precision of traditional laser diode driver is very low, and the operation is difficult, and can not shift between constant current mode and constant power mode. However, the laser diode driver designed in this paper overcomes these disadvantages above, and possesses vivid technical advantage.Traditional laser constant sources are mostly analogue products, whose function is singular, operation is troublesome, protect part is not perfect. This paper introduces a kind of practical Laser constant source with high stability based on MCU. This source is controlled by program of MCU. The final control circuit adopts power MOSFET as current control device, which uses the principle of negative feedback to adjust and stabilize output current. This paper also analyses the stability of output current, and the long term stability of output current can reach 40 ppm or lower.Semiconductor laser driver with good qualities needs to give out stable driving current, and can protect efficiently. It can perform the above function by embedding MCU in the system. The constant driving part mainly uses exact voltage-control current source with negative feedback, and it also uses current-series-negative feedback to attain the effect of constant current. In this paper, we choose high power MOSFETs as constant current devices. It has IGBT, and it has the merits which transistors haven't. Its another merit is that it can gain constant output current with simple driving circuit. Protection circuit includes four parts: delay protection circuit, soft start protect circuit, limited current protection and excessive heat protect circuits. Delay protect circuit is mainly to get rid of surge, using MCU to control relay and direct constant circuit. When the driver is in stable condition, MCU gives dictates to turn off the delay and supports the current of constant current circuits, which prohibits the current aiguille. Soft start protect circuit is to prohibit current step by software counting. Limit protect circuit is to prevent laser from destroying by double protection, including software and hardware. During the work, if the temperature controller is invalid, the excessive heat protect circuit can cut the driving current, and force the laser to stop work to insure the safety of lasers. By using the above projects, it can efficiently assure the safety of lasers.What's more, because there are microprocessors in the system, and according to the clients requests, the constant source we designed has the panel vanish function, that is, when normal working condition, the lights of panel are all turned off, leaving sound alone. This function is cooperated with some optics labs with special requests.