基于单片机的数控直流电流源设计

摘要

利用单片机所具有的智能测控特点，设计制作了基于单片机的“数控直流电流源”。该电流源具有设定准确、输出电流稳定、可调范围全程线性等特点。本设计由两大模块组成：①大功率压控电流源模块；②单片机应用系统模块。前者是电流源的核心，起着恒流调节、抑制纹波电流的关键作用；后者则起着设定电流源输出、改善电流调节精度、消除小电流输出的非线性等作用。本系统由单片机程控输出数字信号，经过D/A转换器（TLC5615）输出模拟量，再经过运算放大器隔离放大，控制输出功率管的基极，随着功率管基极电压的变化而输出不同的电流。单片机系统还兼顾对恒流源进行实时监控，输出电流经过电流/电压转变后，通过A/D转换芯片，实时把模拟量转化为数据量，再经单片机分析处理，通过数据形式的反馈环节，使电流更加稳定，这样构成稳定的压控电流源。实际测试结果表明，本系统输出电流稳定，不随负载和环境温度变化，并具有很高的精度，输出电流误差范围±5mA，输出电流可在20mA~2000mA范围内任意设定，因而可实际应用于需要高稳定度小功率恒流源的领域。

此外，还实现了变增益测量，提高了电流的测量精度。本电流源采用LCD显示界面，使用直观方便。

关键词：单片机，数控，转换，PID控制

Abstract

By making good use of the intelligent measure and control function of the Microprogrammed Control Unit(MCU), the numerical-controlled direct current source is designed and made. This direct current source not only can steadily output, but also can be accurately initialized, and adjusted linearly at a wide range. The design is composed of two basic modules: ①The high-power voltage-controlled current source module; ②The MCU application system module. The former one is the hard core of the current source, while keeping the output current steadily and restraining its ripple. The latter one controls the initialization of the output, improves the precision of the output signal and eliminates the nonlinear effect at the low output terminal made by small signals. In addition, the design realizes the measurement to make the gain variable. In the system, the digital programmable signal from SCM is converted to analog value by DAC (TCL5615),then the analog value that is isolated and amplified by operational amplifiers, is sent to the base electrode of power transistor, so an adjustable output current can be available with the base electrode voltage of power transistor. On the other hand, The constant current source can be monitored by the SCM system real-timely, its work process is that output current is converted voltage, then its analog value is converted to digital value by ADC, finally the digital value as a feedback loop is processed by SCM so that output current is more stable, so a stable voltage-controlled constant current power is designed. The test results have showed that the system can output a stable current, which has no influence with load and environment temperature, and can output a precise current of ±5mA error with a width, which can be set liberally in 20mA~2000mA, so it can be applied in need areas of constant current source with high stability and low power.

so that we improve the measure precision of the current source. Besides, using LCD makes the direct current source more convenient to use.

KEY WORDS: MCU gital-control, transition, PID control arithmetic