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图10为LD驱动控制系统测试平台。由PLT5-450B激光器的数据手册可知,该激光器的额定工作电流范围为0~75 mA,则根据公式(7)可得,对应控制电压范围为0~1 500 mV。实验时使用KEITHLEY-2110数字万用表测量采样电阻两端电压,进而得到LD实际工作电流大小,实验数据如表1所示。
Item Value Control voltage/mV 0 106.89 205.96 306.09 405.06 505.71 606.91 707.82 Operating current/mA 0.045 5.377 10.313 15.293 20.233 25.2405 30.273 35.308 Control voltage/mV 807.75 907.87 1007.2 1108.0 1207.4 1309.1 1409.1 1508.0 Operating current/mA 40.285 45.269 50.215 55.240 60.19 65.255 70.24 75.17 Table 1. Linearity measurement data of control voltage and operating current
根据实验数据,使用最小二乘法对控制电压和LD工作电流进行拟合,拟合曲线如图11所示。一阶拟合方程为:
由线性度计算公式求得控制电压与LD工作电流线性度为:
式中:$\Delta {I_{\max }}$为实际电流与设置电流最大偏差;${I_{\max }}$为最大电流设置值,从结果可看出控制电压与LD工作电流线性度良好。
对恒流驱动电路的工作电流短期稳定度和长期稳定度进行测试,预设LD工作电流为45.25 mA,分别每隔2 min和0.5 h记录一次测量结果,实验结果如图12(a)、(b)所示。
根据实验数据,由稳定度计算公式$\gamma = \dfrac{{{I_{\max }} - {I_{\min }}}}{{{I_0}}}$可得,LD驱动电流短期稳定度为0.014%;长期稳定度(12 h)为0.016%。其中,${I_{\max }}$为实际电流最大值,${I_{\min }}$为实际电流最小值,${I_0}$为驱动电流理论值。
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为测试恒流驱动电路及温控电路对LD输出光功率的影响,设定工作温度为25 ℃,使用机械电子工业部第四十一研究所AV2495光功率计每5 min测一次LD的输出光功率,连续监测1 h,测量结果如图13所示。
实验结果表明,LD输出光功率稳定度为0.205%。
Design of new-style driving and temperature control circuit for low power diode laser
doi: 10.3788/IRLA20210764
- Received Date: 2021-10-21
- Rev Recd Date: 2021-11-05
- Available Online: 2022-03-04
- Publish Date: 2022-02-28
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Key words:
- diode laser /
- constant current driving /
- temperature control /
- FPGA /
- high stability
Abstract: In order to deal with the influence of the stability of the output optical power of diode laser (LD) on the flatness measurement accuracy of the strip laser flatness measuring instrument, a high stability diode laser constant current driving circuit, temperature control circuit and protective circuit were designed. FPGA was used as the system control core. Based on the principle of deep negative feedback, the accurate current control was achieved by the constant current driving circuit. The effective control of LD operating temperature was realized by temperature control circuit based on ADN8830. Driving current was slowly and linearly increased to preset value by improved slow-start circuit, and the slow-start time can be controlled precisely. High reliability and high security were realized by current limiting and electrostatic protection circuit. The results show that the driving current can be adjusted continuously from 0 to 75 mA, the adjustment accuracy can reach 0.025 mA, the short-term stability of current can reach 0.014% and the long-term stability can reach 0.016%. When the operating temperature is controlled at 25 ℃, the stability of the output optical power is 0.205%.