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TIDA-050063: Limited power transfer capability

Roberto
Prodigy 20 points
Part Number: TIDA-050063
Other Parts Discussed in Thread: TPSI3052-Q1, UCC27517

Tool/software:

Hi team,

Because of the limited power transfer capability of the TPSI3052-Q1 it is hard to find a suitable Inductor. I would like to have a smaller peak current so there are more suitable inductors.

This will increase the frequency to +200kHz. That is not possible with the TPSI3052-Q1. Is it possible to use an optocoupler/digital isolator + a Isolated DC/DC converter?

And if yes what requirements does this Isolated DC/DC converter needs to have?

  • 0
    TI__Expert 7991 points

    Hello Roberto,

    Thanks for joining E2E and reaching out to our team! Could you please share your design requirements (voltage, capacitance, time) here?

    Roberto said:

    This will increase the frequency to +200kHz. That is not possible with the TPSI3052-Q1. Is it possible to use an optocoupler/digital isolator + a Isolated DC/DC converter?

    And if yes what requirements does this Isolated DC/DC converter needs to have?

    In the past, we have recommended using a flyback converter for higher power capability in place of TPSI3052-Q1. This article here goes into more depth and walks through a using a new calculator tool we have released to aid in your design process.

    Best regards,
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 20 points

    Hi Tilden,

    The maximum voltage is 1000V capacitance 10mF and time 2s.

  • 0 in reply to Roberto
    TI__Expert 7991 points

    Hello Roberto,

    Thanks for the update. Looks like your system would need 5-A average current, I imagine you were intending to use current thresholds of something like 4-A to 6-A. Understand the challenge, I'm not sure how to use the TPSI3052-Q1 here, take a look at the flyback converter. 

    Best regards,
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 20 points

    Hi Tilden,

    I don't want to use the Low Voltage supply to charge the High Voltage capacitors.

    Is there another options?

  • 0 in reply to Roberto
    TI__Expert 7991 points

    Hello Roberto,

    The flyback converter replaces only the TPSI3052-Q1 in the circuit, does not replace the entire active precharge circuit.

    Best regards,
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 20 points

    Hi Tilden,

    Why do you recommend a fly-back converter and not for example a push-pull?

  • 0 in reply to Roberto
    TI__Expert 7991 points

    Hello Roberto,

    The flyback converter replaces only the TPSI3052-Q1 in the circuit, does not replace the entire active precharge circuit. The flyback converter should be able to provide the power needed for 200 kHz switching frequency.

    Best regards,
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 20 points

    Hi Tilden,

    I understand that the flyback converter just replaces the TPSI3052-Q1. I was only wondering why you propose a flyback converter and not a push pull converter for example?

    How can I calculate the maximum possible frequency for a flyback converter for example?

    Is it also possible to use a Isolated DC/DC coverter like this: SCWN03A-12

  • 0 in reply to Roberto
    TI__Expert 7991 points

    Hello Roberto,

    I am unfamiliar with isolated power supplies and need to read more about them. From a quick overview, it looks like flyback converters are preferred for low power applications, under 150 W.

    Roberto said:
    How can I calculate the maximum possible frequency for a flyback converter for example?

    Keep in mind that the flyback converter or whichever isolated power supply you select for this design is not doing the switching, it's really the gate driver (UCC27517). The isolated power supply is providing a variable current (lowest at the beginning and end, highest in the middle) to the gate driver which ANDs the hysteretic control's output in order to determine when to switch the MOSFET.

    Please take a look at this article which walks through how to design an active precharge circuit using a calculator tool. In short, you would want to find the maximum switching frequency and multiply by the MOSFET total gate charge, in order to find the current needed from the power supply.

    For example if I have selected a MOSFET with 50 nC and need 200 kHz switching at the peak, the current required is 50 nC * 200 kHz = 10 mA.

    Best regards,
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 20 points

    Hi Tilden,

    I didn't see the below formulas before.

    IDRIVER_MAX  =  Qg  ×  FMAX 

    PDRIVER_MAX  =  IDRIVER_MAX  ×  VDRIVER

    I am only wondering. Will the peak currents to charge the gate of the MOSFET not create voltage dips on the supply line that will influence the performance of the Hysteresis Comparator?

    The peak currents to charge the mosfet are atleast 1A depending on the applied voltage ofcourse.

  • 0 in reply to Roberto
    TI__Expert 7991 points

    Hello Roberto,

    I believe the gate driver here, UCC25717, handles the peak source and sink current to the MOSFET and its input capacitor will help reduce ripple on the supply line. A selected isolated power supply should also have output capacitors to help with ripple. I think problems may happen if the isolated power supply is unable to provide the average current needed at peak switching frequency and the MOSFET gate voltage dips to the Miller plateau region. A benefit of the TPSI305x-Q1 is having a UVLO at the output.

    Best regards,
    Tilden Chen

    Solid State Relays | Applications Engineer