Voltage to Current Convertor using LM723

Advertise in delabs

his Circuit converts a voltage control output from a Process Controller to be converted into a Current Control if the AC-Drive or Valve needs a Current Control Signal.

Significance of Current Loop 4 to 20 mA Standard

Voltage to Current Convertor using LM723

This is a three wire voltage to current loop converter. The 1-5 V DC is attenuated and fed to pin 5 LM723 opamp section which tries to maintain the same voltage at pin 10 across the 10 E, thereby producing a open collector constant current sink proportional to the 1-5V input. By trimming the attenuator you can scale-calibrate 1-5V input to 4-20mA output for looping many instruments in series, like a controller, recorder or PLC. With a supply voltage upto 24V, three instruments can be looped. The connection to pin 6 is required to convert 0-1 input to 4-20mA.

All the transmitter circuits can be seen here. Industrial Process Control Circuits

This circuit was designed by me in the eighties, the 555 was for negative supply, The whole thing went into the anodized cast aluminuim head of a sensor.

How 4-20mA Works

More delabs Schematic Diagrams

  • Simple Water operated relaySimple Water operated relay
    This was done in my early days, i have upgraded it, it ought to work, reduce the number of transistors to make it less sensitive, [...]
  • Voltage Attenuator Amp – DMM ProjectVoltage Attenuator Amp – DMM Project
    LF356 opamp FET input is in a inverting amplifier configuration here. R4 + R5 make up Ri each 1/4 W MFR withstands 250V so both [...]
  • FET Current Source and MOSFETFET Current Source and MOSFET
    This is a constant current source using a FET. This is the most simple replacement to series resistor to limit current. The N-Channel FET BF256C [...]
  • Simple Printer Port InterfaceSimple Printer Port Interface
    Printer Port Circuit to see the inputs logic state and drive a few outputs. The preset control program helps test out the circuit operation. Use [...]
  • Triac based Lamp Dimmer power controlTriac based Lamp Dimmer power control
    This is a phase angle control of a Triac which is a evolution from an SCR. The 50 Hz or 60 Hz Sine wave of [...]
  • Edison Bulb Life ExtenderEdison Bulb Life Extender
    The Edsion Filament lamp may be less popular, but it is the most cost-effective light even today. It is very affordable, The light is soothing [...]
  • Battery Level LED IndicatorBattery Level LED Indicator
    This LED Indicator uses a LM339, a quad comparator. LM339 can work on single or dual supplies, it has a open collector output that can [...]
  • Printer Port Logic AnalyzerPrinter Port Logic Analyzer
    This is a Test Circuit for Logic Analyzer software, with the Simple port circuit. The VB Logic Analyzer works, but is just an example program [...]
About delabs 152 Articles
Product Design - Industrial Automation and Instrumentation. -

Be the first to comment

Leave a Reply