• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 13 subscribers
  • Views 1787 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Low power optocoupler replacement in power supply feedback circuit

Carlos Silva85
Expert 4915 points

Other Parts Discussed in Thread: ISO1212, ISO1211, ISOW7840

I'm looking for a digital isolator that can be used as a direct replacement for an optocoupler. The output should be open drain, but without any secondary power requirements. Do we have a part like this?

For the input I would ideally like to have something with lower input power than a standard optocoupler.

  • 0
    TI__Guru 57415 points
    Hi Carlos,

    I believe the opto-couplers that are used in power supply feedback networks are operated in linear/analog region of the device. We currently do not have a device that can be used to transfer analog signal in the feedback network.

    If the opto-coupler you are referring to is used differently than what I have assumed, please do provide more details on how the opto-coupler is used in your application.

    We do have a device that requires power supply on one side but the device is meant to accept only field inputs that are digital in nature, like 24V digital inputs in PLC applications. This is the ISO1211 / ISO1212, just sharing this information in case if you are not aware of this device. Thanks.


    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    TI__Expert 4915 points

    Thank you Koteshwar.

    I can do some loop tuning with the digital output, but the real problem with the ISO121x is the high forward voltage. A typical opto starts conducting at 1V.

    This is the device we are competing, to give you an idea of the specs i need. Secondary requires power, but the primary behaves exactly as a regular opto.

  • 0 in reply to Carlos Silva85
    TI__Guru 57415 points
    Hi Carlos,

    Thank you for sharing additional details, I understand the requirements better now. We currently do not have a device that can provide open collector / drain output and not require power on the output side. If we do plan to develop one similar to the requirement you have mention, I sure will let you know about it.

    In case if this particular requirement can be approached through other options then I would choose ISOW78xx with external BJT/MOSFET. When you operate ISOW78xx with input at 3.3V, it doesn't require output power (as it is transferred internally) and the output channels probably can drive external BJT/MOSFET that are biased appropriately. If there are more channels, ISOW7840 could make the solution cost effective.

    In addition, you did mention the solution to require low input voltage for it to be functional. I am not sure if ISOW7840 with 3.3V input VCC suffices your requirement. I just wanted to make sure I put this idea in front of you.

    Let me know if you have any other questions, thanks.


    Regards,
    Koteshwar Rao