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SM74611 as blocking diode

Hong14351
Prodigy 190 points
Other Parts Discussed in Thread: SM74611

Hello everyone,

SM74611 is designed and marketed as a smart bypassing diode for serial solar panel applications. Has anyone tried it as a blocking diode for solar panel output charging a battery, multiple solar panels parallel operation, or other blokcing diode applications? 

Thank you.

David

  • 0
    Prodigy 10 points

    Hello,

    We're also interested in using this diode as a blocking diode.  I could find nothing useful from TI directly, and found your unanswered question here.  Let me know if you come up with anything and I'll do the same.

    I can tell you short term it seems to work okay.  My worry is with longevity though.  I don't want to put this into 12k products per year just to see half of them come back in a year because this diode is failing.  I worry that consistent exposure to the forward bias state may cause damage (since a by-pass diode would only see forward bias once in a while).

    Ryan

  • 0 in reply to Ryan Daly
    Prodigy 190 points

    Hello Ryan,

    For the same reason (there are only limited information on datasheet available), and I like the low loss and low cost features of SM74611, so I ordered some parts, both SM74611 and SPV1002 for testing. I tested the parts as a blocking diode for battery charging applications, and found those parts worked well for single power source applications. My concern is not the repeated forward biasing, since the internal charge pump circuit is not really stressed, and the parts are designed for 25 to 30 years design life. In solar panel applications, if a PV string is covered up for some reason, it could be a continuous forward biasing scenacio, so the parts are designed for this. My concern is the transient response when the Mosfet is on. When the Mosfet is turned on, it stay condutive in both directions for around 100mS, it could be sensitive to transient or reverse current at this time.

    Thanks,

    David

  • 0 in reply to Hong14351
    TI__Intellectual 2225 points

    David, Ryan:

    Thanks for your interest in the SM74611.  I am one of the application engineers that developed the SM74611.

    As you noted, the SM74611 is designed and tested for continuous operation as long as the max operating temperature Tj = 125degC is maintained.  So that aspect of this applicaiton does not present any issues.

    The issue with the transient response time is for the most part not a concern to the SM74611.  It will provide a low-ohmic path to conduct the reverse current, and as long as the current does not cause overheating or some other thermal failure, the SM74611 will not be damaged in anyway.  The primary concern with the reverse currents is damage to the battery that the SM74611 is expected to protect from negative currents.  If the system is designed such that the transients are slow and the peak reverse currents will be low enough that there will be no damage to the batteries being protected, then the applicaiton should be fine.

    If the Sm74611 is being used to protect a string of solar-cells in series, then the issue with damage due to reverse current is most likely not a concern for the solar panels.  However, in most cases, the reverse voltage rating of the SM74611 would not be sufficient to protect more than a small number of cells in series.

    Perry

     

    Perry

  • 0 in reply to Perry Tsao96839
    Prodigy 190 points

    Hello Perry,

    Thank you for taking the time to answer the questions. More tests are planned for this part.

    David