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VOLTAGE TO CURRENT CONVERTER

Hi ,

I guess this is a rather easy question for you, but unfortunately I do not know the answer.

I want to convert voltage (0v-1v)  to Current ( 4 -20 mA) using the XTR117.

help me out with the schmetic ...

thank you...

Regards,

MRINALINI DHAWAN.

6 Replies

  • Mrinalini,

    I've shown a circuit below that provides the input offsetting and scaling for 0V to 1V input and 4mA to 20mA output using the XTR117. Note that the signal input has an input impedance of 6.25k so it must be driven by a low impedance source such as an op amp.

    This circuit uses the Vreg output of the XTR117 to create the 4mA output current offset. The XTR115 and XTR116 are similar devices that have a higher accuracy voltage reference circuit that can perform this same function with better accuracy and stability over temperature. You may want to consider using one of these devices for higher accuracy.

    Note that this type of 4-20mA transmitter must be used with all input circuitry powered from Vreg and floating. Iret serves as a local "floating ground" and all input circuitry must be referred to this floating ground. External circuitry driving the XTR117 cannot be powered from an external power supply. It is used as a remote sensor device, powered by the current loop on the receiving side.

    Regards, Bruce.

  • In reply to Bruce Trump:

    Hi ,

      Thanks for the reply ....

    we done the connection as per your diagram....as we are giving (0-1v) to I in ,  Iret as ground and +5Vreg (12volt) and all have ground common.

    we are getting 15 mv at I out (PIN4).

    HELP US WHERE WE R WRONG ....

    CAN YOU PROVIDE FULL SCHEMATIC DIAGRAM...

  • In reply to mrinalini dhawan:

    Mrinalini,

    From your description if seems that you have connected pin 3 and pin 4. This will not allow proper operation. See the schematic and comments below:

    Regards, Bruce.

  • In reply to Bruce Trump:

    Hello,

    according to the explanation gived by Bruce, i did this... But i do not have any voltage or current at the output. Now, wich is my Reference pin to measure the VREF and VREG voltage of the chip?  ... Please help me with this, in new making 4-20mA Loops and im just learning about it. I attached my circuit below... Thanks!

    Regards, Ricardo

  • In reply to Ricardo Ra:

    First of all, can you see about 2V on the node between R7 and R8?

    your source impedance seems to be high.

    And Xtr117 has no Vref pin. XTR115/116 have it.  So currently R6 doesn't work.

    And 250 ohm load impedance seems to be high compared 12v loop voltage.

    Simply,  voltage between pin7 and pin4 should be higher than 7.5v at maximum current/load impedance

    Regards

    Hak-Jin Jeong

  • In reply to Hak-Jin Jeong:

    Hello Mr. Jeong!

    Thank you for your comments and for assisting the community.  I hope we see you helping other members succeed in their applications in the future as well!