STM32-Based Drive Circuit Designed For Semiconductor Laser Diodes

As a precise optoelectronic device, the semiconductor laser should be operated in a stable drive current and a constant temperature. The output power of a semiconductor laser depends on the drive current. Meanwhile, the central wavelength is sensitive to the operating temperature. Taking LC96 P series as examples, the dependence between temperature and peak wavelength is 0.02 nm/oC. To ensure semiconductor lasers operating in a stable drive current and a steady temperature,it is necessary to design a specialized drive circuit.LC96P series of semiconductor lasers are hermetically sealed with 14-lead butterfly package and designed as pump source for erbium doped fiber amplifier applications. Aiming at the characteristics of LC96 P series of semiconductor lasers, we designed a laser driver circuit and a temperature control circuit in this paper.First of all, this paper introduces the applications and development of semiconductor lasers, as well as the research of driving technology at home and abroad.Secondly, this paper describes the design of constant current drive circuits, including the selection of the power, the analysis of the constant current drive theory, the protection measures of laser diodes and components selection and so on. The circuit we designed is a continuous voltage-controlled constant current source, mainly consists of operational amplifiers, power MOSFETs, current sense resistors and so on. In the design, we implemented operational amplifier voltage negative feedback principle to realize a stable closed-loop control. In addition, we designed a larger current constant current source through connecting 4 MOSFETs in parallel.Then, this paper describes the design of the temperature control circuits, including the power source design, the implementation of the temperature control system, the research of PID algorithm and so on. The temperature control system is made up of 2 parts: temperature acquisition and temperature control. The temperature acquisition part is mainly about the thermistor measurement. It is so difficult to measure the resistance directly that we implemented the Wheatstone Bridge to convert it to voltage, then the voltage signal is amplified by operational amplifier and measured by A/D convertor. The temperature control part is mainly about the design of Thermal Electronic Cooler drive circuit. We implemented D/A convertor to control MAX1968. Then MAX1968 outputs bipolar current and drives the Thermal Electronic Cooler, thereby cooling or heating the laser.Finally, this paper describes the STM32-based control and human-machine interface design. In the constant current drive circuit portion, STM32 reads and displays the sampling data of current, and outputs the digital-controlled voltage signal. In the temperature control portion, STM32 acquires and processes the temperature signal, as well as controls the laser temperature by PID algorithm. In the human-machine interface, we realized the function of settings save, key input and display.The experiment results demonstrated that the design of constant current drive circuit is capable of providing 0 ~ 950 mA current for LC96 P. In addition, the constant current drive circuit with 4-channel MOSFET can provide the output current up to 10 A, taking rectifier diodes as a simulated load. The temperature control circuit can control the working temperature of LC96 P at 25 oC, with accuracy of ±0.1 oC.