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Применения > > 4-20 mA Low Power, 14-Bit, Process Control Current Loop Transmitter

4-20 mA Low Power, 14-Bit, Process Control Current Loop Transmitter (cn0179)

The circuit in Figure 1 is a 4 mA-to-20 mA current loop transmitter for communication between a process control system and its actuator. Besides being cost effective, this circuit offers the industry’s low power solution. The 4 mA-to-20 mA current loop has been used extensively in programmable logic controllers (PLCs) and distributed control systems (DCS’s), with digital or analog inputs and outputs. Current loop interfaces are usually preferred because they offer the most cost effective approach to long distance noise immune data transmission. The combination of the low power AD8657 dual op amp, AD5641DAC, and ADR02 reference allows more power budget for higher power devices, such as microcontrollers and digital isolators. The circuit output is 0 mA to 20 mA of current, and it operates on a single supply from 8 V to 18 V. The 4 mA to 20 mA range is usually mapped to represent the input control range from the DAC or micro-controller, while the output current range of 0 mA to 4 mA is often used to diagnose fault conditions.

The 14-bit, 5 V AD5641 requires 75 μA typical supply current. The AD8657 is a rail-to-rail input/output dual op amp and is one of the lowest power amplifiers currently available in the industry (22 μA per amplifier over the full supply voltage and input common-mode range) with high operating voltage of up to 18 V. The ADR02 ultracompact precision 5 V voltage reference requires only 650 μA. Together, these three devices consume a typical supply current of 747 μA.

The circuit has a 12-pin Pmod™ digital interface (Digilent specification).

Figure 1. Low Power 4 mA-to-20 mA Process Control Current Loop (Simplified Schematic: All Connections and Decoupling Not Shown)


  • Low power 4-20 mA current loop
  • 12-, 14-, or 16-bit digital control
  • Use in programmable logic controllers


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