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INA250: sensing NEUTRAL conductor current in AC mains application

Part Number: INA250

Has anyone tried using the INA250 in a lines powered AC application to monitor the current on the Neutral conductor?

Obviously the INA250 would have to be configured for bidirectional operation.

Thoughts?

  • Hi Steven,

    Thank you for posting on the E2E forums.

    Technically it is possible to do it two ways:

    1) By referencing the REF input to 1/2 of your ADC voltage range (For example, on an MCU powered by a 3V3 rail, with an input voltage on the INA250 REF pin of 1.65V, an output of 1.65V would represent zero current flow, an output of -1.65V to 0V would represent full scale on the negative half cycle and an output of 0 to +1.65V would represent the current on the positive half cycle. Software side this requires a loop to separate the received values into two variables and the offset to be calculated at startup (The ADC reading at 0Amps).

    2) For less demanding applications you can reference the INA250 REF input to Ground. In this case you have the current measurement every half cycle, so it is always positive and allows the full usage of the ADC resolution, but might not work on certain devices that do not draw power symmetrically from the mains (half wave rectification).

    We have EVM's for the 250 on site, so tomorrow I set up a low voltage AC transformer and perform some measurements for you.

    Kind Regards,

    Carlos S., TI Sensing Products, Applications Support

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Carlos Silva85:

    Thanks;

    Also, according to the data sheet, the recommended continuous max current is +/- 15A.

    Some UL/IEC/ANSI specs that guide the design of this product in question requires testing with surge currents up to 45A.

    The test is 50 reps of 1 sec surge and 9 sec cool down.

    What comments can you provide on the surge tolerance of the INA250?

    This would potentially be used in a billing grade energy meter.

    Best, Steve

  • In reply to Steven Dunbar:

    Hi Steve,

    Do you require the surge current to be within the linear region of the amplifier or do you only require it to withstand such transients?

    Kind Regards,

    Carlos S., TI Sensing Products, Applications Support

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Carlos Silva85:

    It just needs to survive. Normal operation would be well within the Recommended rating.
  • In reply to Steven Dunbar:

    Hi Steve,

    45Amps is a little bit too much for our device. I am also concerned what would happen under a short circuit condition, when line peak currents exceed 100A for a short duration before the circuit breaker trips.

    I would suggest using an external sense resistor that could be sized to cope with all these variables for design robustness. 

    As to the current readings, AC is fine as described above.

    With the grounded reference there seems to be some discontinuity on the start of the waveform, but otherwise as expected



    With the reference at 1/2VS and VS = 5.0V

    The plots are a 18Ohm load in a 12VAC supply, differential measurement, INA250-A2.

    Kind Regards,

    Carlos S., TI Sensing Products, Applications Support

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Carlos Silva85:

    Steve,

    Further to my posts above, I would like to make you aware of TI design TIDA-00753 which uses a current transformer for high-accuracy, wide-range AC current measurements and seems ideal for your requirements.

    Please let me know should you require further assistance.

    Kind Regards,

    Carlos S., TI Sensing Products, Applications Support

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Carlos Silva85:

    Thanks for the update; the current solution is based on a current transformer; I was looking for ways to reduce the size and cost.

    I will keep this approach in mind, but as you said, it might not survive the UL required surge testing.

    Thanks, Best, Steve