基于HART总线智能变送器的电源分析与设计

以微控制器为核心的智能化技术和现场总线技术近年来成为仪表行业的研究热点。与普通的4~20 mA变送器相比,基于HART总线智能变送器节省了大量电缆,提高了测量精度和可靠性,但同时也增加了仪表内部功耗。仪表的电源部分设计变得十分关键。介绍了HART协议的特点,分析了HART总线智能变送器的低功耗和变仪表电流特性,并对低压差线性稳压器和开关式稳压器做了性能比较,指出线性稳压器成本低,不易受电磁干扰,纹波电压小,缺点是电源效率低;而开关式稳压器的供电效率较高,输出功率大,不足就是输出电压中所含纹波较大。传统单稳压电源设计模式不能同时满足高效率和低纹波电压要求,提出了一种二级稳压电源设计方案,将低压差线性稳压器和开关式稳压器配合使用。实例证明该方案达到了设计要求。

Analysis and Design of Power Supply for Intelligent Transmitters Based on HART Bus

Intelligent techniques with the core of micro-controller and field-bus techniques have become one of the research focuses in instrument industry in recent years.Comparing with normal 4~20mA transmitter,an intelligent transmitter based on HART Bus can save lots of cables,increase the measuring accuracy and reliability.However,it consumes more power than the normal transmitter.Therefore,it is desirable and important to design a more powerful power supply for such instruments.This paper firstly introduces the features of HART bus protocol.And then it analyzes Low-power and various-current characteristic of the intelligent transmitter based on HART bus.Thirdly,based on a comparison between Low Dropout Linear Regulator and Switching Regulator,it points out that Linear Regulator has lower cost and is not easily influenced by electromagnetic interference with low ripple voltage,but its power supply efficiency is not high.In contrast,Switching Regulator has a higher efficiency with a higher power output,but its ripple voltage is not ignorable.Therefore,traditional design mode of single regulated power supply will not meet the requirements of high efficiency and low ripple voltage.Finally,this paper presents a method by combining Low Dropout Linear Regulator with Switching Regulator based on two-class regulating.The proposed method has been tested using an example and it has been convinced that the design requirements have been satisfied.