在实际应用中，很多时候需要输出电压、电流等信号，特别是在工控行业中，4-20MA的转换经常要用到，选用AD421芯片来做的话，成本颇高，如果采用单片的PWM输出来做DA完全可以做到14位以上的精度。-In practical application, and many times need to signal of the output voltage, electric current and so on, especially in the industrial control industry, 4-20 ma transformation often want to use, choose AD421 chip to do it, cost is high, if USES the single chip PWM output to the accuracy of the DA can do more than 14.