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TIDA-00173: Breakdown voltage of the TVS, selection of the resistor and voltage regulator

Joyce Chen
Intellectual 1190 points
Part Number: TIDA-00173

Hi team,

What is the relationship between the breakdown voltage of the TVS pointed by the blue arrow and the Vds voltage of the MOS in series?

How to choose the resistor and voltage regulator that be pointed to with the red arrow?

Many thanks.

  • 0
    TI__Intellectual 960 points

    Hi Joyce,

    The breakdown voltage of the TVS (D15 + D16) should be lower than the Vds rating of Q2 (950V in this case) minus some necessary margin.

    It also should be close to the middle of the highest possible drain voltage of Q1 so as to devide the voltage pressure to the two MOSFETs.

    In this case, consider a 1200Vdc max input, plus a 300V reflect voltage and a 200V surge, the highest peak voltage may reach to around 1700V.

        

    So D15 and D16, add up to 840V max, are used to clamp the gate voltage of Q1 when Q1 and Q2 are turning-off.

    D31 will clamp the Vgs of Q1 to be not over 12V, which is a typical driving ON voltage for power MOSFETs, when Q1 is turning-on.

    As for the resistance of L1, it should be small enough to drive Q1 and high enough to work with C42 and/or Cgs of Q1 to filter out any transient noise during switching. Notice the 850Ω of L4 is its typical impedance at 100MHz. Its impedance is merely 20Ω at 1MHz and 0.1Ω max for DC.

    Besr regards,

    Jerome Shan

     

  • 0 in reply to Jerome Shan
    TI__Intellectual 1190 points

    Hi Jerome,

    Thank you for your reply.

    Besides, my customer met a problem in the debugging process. When the two MOS in series are running, the temperature will rise relatively high, about 84 degrees, and the temperature of two TVS in series will reach 105 degrees. If there are any measures to reduce the temperature rise for this temperature?

    Thanks.

    Joyce

  • 0 in reply to Joyce Chen
    TI__Intellectual 960 points

    Hi Joyce,

    Have you tried to reduce C42 to a lower capacitance one or even remove it?

    Best regards,

    Jerome