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TIDA-01385: Measuring the current from CT

Jonjan Hoxha
Prodigy 40 points
Part Number: TIDA-01385

Hello,

we want to use the energy harvesting reference design to power up a system with peak consumption 50mA, but we also would like to measure the current of the CT by using an ADC. Is there a reference design for this? Do we have to "separate" the 2 operations i.e. charging/supplying the current to the system and measurement or is it feasible simultaneously?

Thank you.

  • 0
    TI__Genius 13835 points

    Loop Travis to support this case, regarding with TPS61021. 

  • +1
    TI__Expert 8925 points

    Hi Jonjan,

    If your design is not very sensitive to efficiency, you can connect a sampling resistor or uses a Hall sensor:

    Solution1:

    This solution measures the rectified current, which is the absolute value of your CT current.

    Solution 2:

    This solution can measure the AC side current with an DC offset.

    Solution 3:

    This solution provides isolation between power circuit and signal circuit and therefore have better reliability.

    Best Regards,

    Travis

  • 0 in reply to Travis Wang
    Prodigy 40 points

    Hi Travis,

    thank you for your prompt response. It was very useful. In our application we would like to measure the AC current so that we can calculate and measure several parameters other than the absolute value of the current.

    I have some further questions/doubts:

    • We are using a differential ADC that has a max range of 600mV on each side. How would we feed the signal to it? 
    • Would you please suggest us a hall sensor for this application? The max current in the secondary of the CT is 1A in our case.
    • If our interpretation of this reference design is correct, the Q2 limits the voltage accross the supercap at 2.6V. Does it mean that if the system needs the current and the CT is able to provide it, it will still get the power from the supercap instead of the CT, or is the current flowing to the boost converter under normal conditions? We would like to use the supercap only if the current from the CT is not sufficient otherwise we would like it to feed the boost converter directly.
    • We will use the device on a three-phase system. Is it possible to supply the system using more than one phase or does the complexity become too much for it to be worth?

    Best regards,

    Jonjan

  • +1 in reply to Jonjan Hoxha
    TI__Expert 8925 points

    Hi Jonjan,

    1. Please check the datasheet and see if you can connect one ADC input to GND and use it as a single-ended ADC. And you can reach to the support team of that ADC for further advise.

    2.Same reason as 1, I shouldn't be giving advise on that Hall since it's not our product.

    3.The boost will get the power from the supercap as soon as the Scap voltage reaches 2.6V. Extra power stage is needed if you need a direct power path. I would like to know why you want a direct power from the CT.

    4.It is possible. But for most cases it's not worth the cost because usually three phase system is applied for high power applications where single phase net cannot support that heavy load.

    BR,

    Travis