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SN6501 Bipolar High-Voltage Half-Wave Rectifier Circuit

Greg
Expert 1961 points
Other Parts Discussed in Thread: SN6501, TPS55010

I would like to use the SN6501 to generate a +/- 20V isolated supply that I will regulate down to lower voltages. The data sheet shows examples of ways to generate higher output voltages. Figure 48 in the data sheet shows how to generate a high voltage bipolar supply, but I think there might be an issue if the positive and negative outputs are not equally loaded. The other examples are OK because they are either full-wave or unipolar. The problem with half-wave bipolar is that one transistor of the SN6501 ends up driving the positive supply, and the other transistor drives the negative supply. Won't this cause a core magnetization issue because of the imbalance? If so, how much imbalance would be acceptable? I will be using the 1:2 Wurth transformer and a 5V supply for the SN6501.

Thanks,

Greg

  • 0
    TI__Intellectual 2200 points
    Hi Greg,Sorry for the delay in this reply.
    As per our offline discussion, I agree with you that there is a chance of asymmetric core magnetization due to unequal load on the bipolar supplies. Just to be sure I am checking with the author of the circuit in question, and I'll get back to you once he responds.
    Rgds,Anant
  • 0 in reply to Anant Kamath
    Expert 1961 points
    Hi Anant,

    Thank you for asking the author about this and confirming it. Hopefully the datasheet will be updated with information about how much of an imbalance is acceptable. It appears those Wurth transformers don't have a lot of margin in this design. Fortunately TI has solutions using Wurth transformers that are capable of producing higher-voltage isolated bipolar outputs. They also have overcurrent protection, which is something I am concerned about with the SN6501. It would be good if TI would either upgrade the SN6501 to include overcurrent protection, or develop a linear regulator that has a programmable current limit via a set resistor. EEPROM-based resistors could be used to adjust the current limit that way.

    Regards,
    Greg
  • 0 in reply to Greg
    Expert 1961 points
    I should add that Anant had heard back from the author, who agreed the transformer will saturate if the loads are asymmetrical.

    Greg
  • 0 in reply to Greg
    TI__Intellectual 2200 points

    Hi Greg,

    Thanks for your comments. We do not at present have data or analysis to directly comment on how much load mismatch is allowed for the circuit in Fig 48 of the SN6501 datasheet. We will consider evaluating this circuit in some more detail in the future and updating the datasheet accordingly.

    Your suggestion for an adjustable current limit for an upgrade of the SN6501 is also well taken.

    Rgds,

    Anant

  • 0 in reply to Anant Kamath
    Expert 1961 points

    Hi Anant,

    Thank you for looking into this.  I am researching other options, of which the TPS55010 might be a good alternative.  I would like to point out one more thing about the SN6501 and the E2E Forum.  When you start a new topic and type in a part number, the forum software suggests the Non-Isolated DC/DC Forum.  I didn't post there because I saw a post from a TI employee that said the Industrial Interface Forum is the place to post questions about the SN6501.  Here is a screenshot of what it looks like:

    It would be good if this was changed.  The recommended forum for the TPS55010 is also the Non-Isolated DC/DC Forum.  I think that one is also wrong.

    Thanks again and have a great holiday season.

    Regards,

    Greg

  • 0 in reply to Greg
    Expert 1961 points
    Hi Anant,

    Forget my last posting about the SN6501 and which forum it is found in. I found the forum for the E2E Site Forum and I will post it there.

    Thanks,

    Greg