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Non-isolated voltage or current measurement for high voltage application

P SUBRAHMANYA ADIGA5
Prodigy 80 points
Other Parts Discussed in Thread: TIDA-00639

Hello,

I understand that when we have high voltages in the circuit, isolated V and I measurement is necessary because of regulatory/safety requirements. However, still i could see some references suggesting non-isolated measurements such as TIDA-00639 (http://www.ti.com/tool/TIDA-00639). I am confused about when we can go for non-isolated measurements and is it bound to regulatory requirements if we go for non-isolated measurements.

Regards,

Adiga

  • 0
    TI__Guru 52980 points

    Hi Adiga,

    In most cases, the isolation requirements are driven by the end equipment standards but when a system needs isolation is really dependent on the application. For example, if the measurements are only to be displayed on a small LCD that is part of the meter then isolation may not be required. If the measurements are to be transmitted to external systems through wired communication like RS-485 then isolation is necessary either between the MCU & RS-485 transceiver or between analog front end and MCU.

    The requirement differs from one application to another, if you could tell us what your end application is then I may be able to comment if isolation is necessary for your application. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 80 points

    Hello Koteshwar,

    Thank you for the answer.

    This query is general and not particular to any specific design. I would like to know about how to decide should we go with isolated or non-isolated measurements.

    Regards,

    Adiga

  • 0 in reply to P SUBRAHMANYA ADIGA5
    TI__Guru 52980 points

    Hi Adiga,

    Thanks for your inputs. Isolation is usually needed in 3 situations that are described below.

    1. Where there is a possibility for high voltage surges that may damage equipment or harm humans. Examples include most industrial automation systems with communication or field input/outputs.
    2. Where interconnections involve large ground potential differences (GPDs) and disruptive ground loops are to be avoided. Examples include RS-485 and  CAN bus interfaces.
    3. Communication to high side components in high voltage systems. Examples include gate driving in motor drives & solar inverters.

    Apart from above, isolation can be used for level translation, to improve noise immunity and to meet some of the EMC requirements. For all the use cases described above, even though isolation is most suitable option to meet the requirements there could be other ways to achieve the same function.

    Let me know if this answers your question on deciding when to use isolation, thanks.

    Regards,
    Koteshwar Rao